Hi, it's multimeter repair time or at least evaluating a returned BM um 786. They don't fail all that often. Still got the Uh protective I don't know if they're using it with the uh protective uh film on it or they just had it in the box and they put it back. hands up if you do that.

Oh, hands up if you leave it in the comments if you actually use your film, especially when it's like daggy like that and it's really obvious I've used stuff for you know, donkey's years with the with the film still on it. if it's like completely not obvious sometimes I've like used uh products and I got like I realized like five years later oh there's a film there yeah flapping around in the breeze there. Yes, the uh, the bryman meters do fail. um there's not a zero percent fire rate I'm not actually keeping figures on this I wish I did occasionally like I'll have to send out a new meter or whatever I don't bother like I don't offer a repair service I thought I'd have a look at this one.

uh because yeah, it like it doesn't turn on. apparently they assured me it's not the batteries, it's pressure on the battery pack. no okay, um, let's crack her open and see what's what. And of course the 786 uses quite unusual uh battery pack.

pull that like the three, the vertical three Triple A's like that that one's that one's sitting out a bit but that looks good so it connects with one tab thing down there. So I've got a gold uh flashed pad down there and a spring contact and that contacts that metal tab there. So the spring contacts that and then there's that little tab over there so that tab's there that should work the springs in place. Let me, um, let me measure the voltage here again.

4.4 volts that should work I'm not seeing anything out of place there. You can see that Mark on the PCB there where that that is my contact so that's obviously touching. something's failed in inside and it's written there. nominal 4.5 volt battery negative on the pad and we're getting positive.

Okay, so the pad is the negative one. Oh yeah, I can see that going down there. Yep, that's spring which is actually soldered to the PCB. It's not a uh, it's not just flapping around in the breeze sitting in that little holder there.

so I can hook a power supply onto that. hang on. This is right up under the bench. Better make sure I've got it right.

And they use a black terminal I Can't show you this. So I've got there's National Instruments Virtual Bench uses a black terminal for the positive uses all black terminals. It's only like the ring around the back. you can't actually see it, You gotta? Oh, it's just anyway so we should be able to see like a couple of milliamps whatever the drawer is if this actually Works No, no, it's kind of work current limit what? let's drop into point eight.

Something's going on there. Oh yeah, I had it backwards. Oh all right, that's embarrassing. So that's the reverse protection diode there kicking in.

All right. it's positive on the pad and negative on there. Here we go. uh uh nothing.

can we see that? LCD no no LCD oh He's dead Jim Not seeing anything obvious, you wouldn't expect to to take out the screen I Think to get to processor but the problem is you take out the screen, you can't see if the thing's on or not. You know you have to rely on the current draw. So anyway, could it be a bad contact? like range switch contact? because that's where the actual switch is in this thing to switch it ons. Even though they they trust me to have the firmware and the firmware reprogramming tool which they won't give to anyone else.

but they won't trust me with the schematics. so I don't know. Don't get it because you know, like what if I did want to have offer a repair service you know I mean geez I'd like to. You know it's like for something like this just doing a video you know I've signed an NDA with them I wouldn't actually release it.

there's our as the bottom BTC is uh Bryman that's Bryman branded. so yeah, where's the um protection? I can't remember. kind of look at my own tear down photos. So I do have tear down photos.

of this. There's no protection diode up there. not on this side. Remember it's solder-wise Everything's looking good around there.

No workers be easy If I had a schematic. Anyway, like next Um thing would be I Guess remove the range switch. and because the brain switches, you know you go for a mechanical fault. Anytime you've got a mechanical versus electrical, always go for the mechanical first.

Don't assume it's electronic e and flip, that's the mechanism. It's got a little bit of grease in there that goes around there like that now. I've got to get it back in its original position. But anyway, contacts.

They look good. Not seeing a problem there. They look the correct height, they're not worn, they're not pushed in, they haven't fallen out. So contacts are good.

But no on a multimeter on something like this that has a mechanical power thing, you definitely want to suspect that, but that's shiny as a C-3PO look at that. so the next would be you can see the switchware down here, but that looks good. So yeah, they've got labels around here. So which one's actually the power switch? It's usually one that goes like right around.

Okay, so I'm gonna Buzz this sucker out point four Ohms there you go that is low. Jab it right up there right up the clacker and see if we can get the positive 0.3 There you go. So that outer one is your positive and that inner one that's your negative. Okay, so it's getting through to the contacts.

there's no contact like you'd look for contamination on there as well. Like you know, if it's customer return one like you wouldn't rule out, let's build something on it or something like that, but there's nothing. Nothing that's obvious. Quite happy with the looks of that.

A few little normal wear marks from the range switch, but not a problem. I've had that before. People have returned, not multimeters, but I've had people return stuff and uh yeah, and they've um, they've fiddled with it I didn't fiddle with it, but uh yeah, they have. So I can't see any reason to suspect the rain switches at fault there.

So I guess now um I need to put it back together, feed in a voltage, and then make sure it's getting to the processor because I like the process could be active, it could be drawing now for all, but you know it could be getting there and not another process could be dead. The LCD driver could be dead anyway. I am going to rule out the range switch. That one there is the positive did we say and that inner one and then the second inner ring is the negative switch.

It doesn't look like to be switching any of the negative there because the negative I think this is the off position I Don't know, you know how that actually lines up precisely. You can see the labels down here off. AC Volts If you try and decode these things, it's not going to switch in the negative, it's going to be switching the positive. You know, like this, we measured as the positive input, so it's switching it through to this one.

So the contacts on the back of the switch that one there is is doing the encode the encoder like the switch in between this and this. So This ground here is doing the sensing to tell the processor which switch position it's actually in. So that's what the negative is doing. So obviously it's you know it's pulled High probably inside the micro and it's just so.

that's how it reads the switch position. But the next, the next two rings. these two are. well, at least this side of it.

You can do other decoding on the other side, and that's why they have different ones on opposite sides like this. Okay, so they do decoding in. You know they do sweet power switching and decoding. Anyway, there's a gap in there, so in the off position, well, it's off.

It's disconnecting the power. but as soon as you move it from here to the next position which is the AC volts, Boom! It joins the two of these like that and you can see it's got a little break in there that's actually a break before make. So they're doing something. They're doing some break before make.

thing in there. So I don't know why was that Doing a power on Re Is that a power on reset? Is that why they've got the mate before break? Don't know. So we've had a schematic. be able to tell you and uh, then we're going to have to measure the voltage on the processor.

So yeah, all right. So I don't have the resolution on the Uh power supply here. I've only got that one milliamp and occasionally it does flicker to one. So I've put the current meter which is isolated from this thing in series.

so let's see if this works. Let's go to 100 milliamp range. Yeah, there you go. 0.68 milliamps.

so there's something there. but I'm pretty sure that's not the operational. that is not the operational current. Okay, so I've got it in the case and I think I've switched it to off.

Yeah, there you go. I really need a sharp probe here instead of this banana plug? That's all right. I've got a current limit there and I've got a nice uh, 30 milliamp current limit as you can see up there on the power supply. So even if I can use this as a probe to point to the first time, I've realized that.

Okay, so it's off and switch it on. Yeah, there you go. 0.68 Uh, is it getting to the processor? I Don't know. That is the multimeter chipset that's not the Um processor.

the processors on the other side of this thing. So now of course, if I was getting serious, onto this. I would like solder a uh little uh wire onto there. Well onto here.

You don't want to contaminate that pad. um because that will ruin your day when the Press fit. Um, you know contact Spring contact comes down on there like that. but I'm too lazy for that and I'm the glutton for punishment.

so I'm just going to keep going. Damn it. Now the good thing is is that I do have my power supply hooked up So and it's hooked up to the multimeter as well. So it's the common so it's already there as the Uh common.

So I could actually you know probe around stuff like this. Let's probe a cap there. There you go. Yeah, 670 Okay, well.

1.84 volts, 1.8 sounds like a voltage that you'd have once again. I Don't don't have the schematic so you know. So yeah, yeah, like we're getting something there. What's this one over here? Again, this is where the schematic would come in handy.

That could be part of like the true RMS uh thing or something. but yeah, there's not much doing over here. Well, the process of goodness is on the bottom side and it's under the LCD Clearly we've uh, we're out of the realm of a like a simple problem like a contact problem with the battery pack, a range switch, uh, problem. It's obviously there's power getting.

um to the circuitry. uh, there is actually a slight history of bryman, uh, processors actually just going tits up. um, like over a long period of time. although I think this is a fairly recent order I think it's like only a year or less than a year old or something like that.

But in the Uh 235, which I've been selling for a long time, like seven or eight years now I think a few of those have actually, just you know, it's just failed the the main chippers, uh, failed and so yeah, we're not sure you know. is it silicon rot in the dye or something like that? I'm not sure what the Uh deal is there, but um, yeah, so you know, maybe something's died in there. But yeah, I mean it could be like the uh LCD driver chip. Yeah, we're getting into serious troubleshooting territory now.

All right. So I soldered a wire on I've removed the LCD as well. so now we can access the other side of the board. so just check in here so we can get this.

uh, that's four and a half volts coming in and our current is Auto ranges back. That's annoying every time there you go. 0.678 milliamps. Unfortunately, like you've got to be careful because it will time out.

You remember all the multimeter has Auto turn off so maybe we should feed a continuous voltage in make it do something. I Was going to say that you could actually, uh, put it to Ohms mode. for example, put the probes in and see if it can go to continuity mode and see if it can go through. and uh, even though you don't know what mode you're in, go through and see if it buzzes.

but uh, yeah, 0.68.6 milliamps is not right. So anyway, we can now flip that over. I Probably should have put I'm just going to ruin that spring aren't I So yeah, this goes over to the keypad, that one and that there. since something like the ground spring here which goes to the it's not the battery negative, it's actually the Guard Ground of the circuit which goes.

that spring goes to the shielding in the back of the case that you don't expect that to be ground so that's at some voltage there. Um I don't know whether or not that's correct. Once again, don't have a schematic so don't know, but I do know it's not zero, so that's good so that you know there's there's voltage going going on in here so it's scope time now. unfortunately.

Um I don't have this machine set up to view this scope. like showing both at once. I haven't got my ATM set up for that. So I just probe the rail there.

the battery. There you go. Four and a half. Okay, well let's see if we got any oscillation on our clock, shall we? Well, there's your problem.

Uh yeah, no clock using time. send probe so we're not loading that down too much. But yeah, um, oh, what's I know I Thought that was a little blowhole there for a second. No.

So yeah, we're getting no, no clock on our processor. So that's a problem. Just occurred to me. What I could actually do is hook this up to the programmer and see if the like and power it through the programmer.

Is that a short sort of short on a pin? No, this looks like a bit of plastic or no. that's it. That's no, that's a bit of fluxy. That's not going to stop the processor working though.

Okay, what I'm going to do is probe these caps here. So if I probe those, you can see that there's not much happening there either side of those caps, right? We're getting something a little there. I Expect that to be bulk decoupling for the chip here. I Mean you know this.

This looks for all the world. Like, you know, power input pins, right? So it seems like the processor is not getting it's, not getting voltage. We've got a regulator over here. Is that it? Let me probe.

Ah there. Okay, that's four and a half. You can't see that, but that is. uh, the four and a half volts.

Okay, so the four and a half volts going in, That'd be the output. Ah, I Can you can't see that? There you go? Um, yeah, that's uh, the 3.3 So we're getting our 3.3 volts. there. Is there anything like 3.3 volts happening on the micro? There doesn't seem to be.

So why the switch position is on? Um, well, we know that because it switches it through to the regulator. So here's where it'd be like, super handy to have the schematic just saying. Bryman. Anyway, we are on the right track.

I think I've got a solder of wire in there I Don't like that. Turns out that's actually a 3.5 volt rail. There you go, but doesn't seem like any of that is getting to the processor. I Know there are different grounds in here for like the analog subsystem and things.

but the. but the actual processor? Um, should just be a regular 3.3 Volt or whatever. 3.5 in this case, maybe. uh, processor.

it should be sharing that ground. Like, even if I use another multimeter which you can't see here, cap there like I'm getting I'm getting 0.13 volts. No, No no no, no, that's wrong. Now this is interesting On the other side here.

we've got two transistors Q19 and Q18, and here's our 3.3 A 3.5 volts. Okay, it ain't coming out so it's got a 10K pull up. Unless there's a no, there's no. there's no.

Via jumping down to the other side, it goes through a 10K resistor. What is that doing? Um, it's just pair like it's a big fat Trace too as if like it's a Power Trace rather than a signal. Trace but it goes nowhere. um, except through this.

10K resistor. Yeah. Power switching. Go into the processor.

Look that uh I've had a little little rework there that is not a Reflow somebody used some excess solder there I assume that's from the factory and the uh, the customer hasn't uh done that. but you never know. But yeah, now we're getting into some interesting Electronics debugging. at least.

All right. So I hooked up the uh programmer to this thing. I actually programmed a good Uh unit with the latest style firmware to make sure everything was working fine. Then I plugged it into this one and it doesn't work.

So the processor under here. um, this is it's just not detecting it. Uh, the program. It doesn't detect it.

and this thing you program in the off the switch off position. so it actually supplies external power to here so it bypasses any other switching. that's um, happening. So yeah, if it can't read the processor, then yeah, something's wrong.

But that doesn't explain why we're getting no voltage to the processor on. Uh, when we switch this thing on since even if the processor was dead, somehow, you know the Silicon just doesn't work. Um, then it'll at least get voltage to it. Found something that can, actually, uh, switch this.

Let's probe it here like this. And if I switch on, you can say that it switches through to this. So yeah, it's actually, um, there'd be a cup there. It's going to slowly discharge.

Yeah, so that it's doing the business right. So why does that power not get through to the main processor seemingly? I'm gonna have to Tracy Trace Yeah, So the output of that regulator, it drops through here. it doesn't go anywhere else and then through a zero Ohm resistor to here, right? So that's it. That looks like that's the extent of the path.

Hang on. We are getting our three and a half volts there. Okay, so that's going through to here. So what I thought was a well.

This could be like a star ground. Okay, because you don't know. Like because the voltage rails inside these multimeters are they're not floating is not the correct term, but they're shifted. and they're You know, they're all over the shop.

So unless we had the schematic, um, hard to see. But basically, that transistor's fine, right? So we have the power coming in here where it goes through a zero Ohm resistor. It goes into this transistor and it comes out this transistor here. So that's fine, right? So we're in three and a half volts going over here, powering everything back.

that goes over to here. Oh no. see that. that must be a different ground.

Okay, so that's why we're because I'm using the common ground at the moment. I'm not using two probes to probe a differential Hang on that's just switched off. should. I What? What happened there? Okay, switch on four and a half volts goes through over to here.

three and a half volts out of the regulator. Okay, it drops down. There's a whole bunch of ears there. It drops down here over to here and then switches through.

Oh no, now it doesn't. It did before you saw it. What the what's wrong with that little sucker down there soldering wise. it looks fine.

Oh I swear. I'm not going nuts, right? I wish I could replay the video right here in front of me. I'm sure that was switching it through. You saw that before.

Okay, well this is starting to get very silly. Um, this is where I have to start. like almost reverse engineering and looking up part numbers and stuff like that. So what I've done is I've actually, uh, hooked this up to the programmer here and I can't show you that for a confidential hourly reasons.

but um, it doesn't detect the chip. So the interesting thing about this is that you program it in off mode so it actually bypasses all the power. IT Supplies Power through the connection interface here, which is this little pin header over here. It doesn't detect the chip.

So even bypassing this uh regulator here, which uh, We've determined, uh, switches on in when you actually switch the meter on, it switches that. but also because uh, multimeters have power off functionality. That's clearly what I believe that's what these transistors down here are doing. This is the the auto off functionality.

so this is like a processor latch thing Now we've seen that it uh, when we did have it actually latch power on the output here, but then it didn't later on. so I didn't I don't know what's going on there? Maybe I don't know. Process is half booting up and latch it on and then dying I I Got no idea, but obviously the programmer is not being detected, so there's something wrong with at least when you bypass it. Like everything else taken out of the equation from the multimeter circuit, this thing is not being detected when you plug into the programmer header.

There's just no point chasing a red herring down a rabbit hole there. Um, if we can't get this thing to detect when we at least plug it in here, so it could be the micro dead could be some other part of the circuit that's being used by this external power thing. So what I'm going to do now is I'm going to plug in the external power here and I'm going to work from there to see if if we actually get power on this chip because I think these two have to be the Power Pin Now here's another interesting thing: I Supposedly know the exact type of this microcontroller. I Downloaded the PDF datasheet for it.

It's not available in a 48 pin Lqfp here. Um, it's just not. it's just not available now. they do have a lesser range in a 48 like a slightly different variant in a 48 pin.

uh job. But the PIN outs don't match at all. So and of course look like we've got a decoupling cap here. like huge big veers like this is ground okay like this is power Okay and like huge chance here, right? this has to.

these two have to be the Power Pin and it doesn't match the data sheet at all. So I think they've got some custom pin variant of that. The manufacturer has made it for them which they'll do if you've you know, significant enough customer, no worries. What I've done is just put a texter Mark there.

so I know exactly where the off position is. I'm not going to get confused so that is definitely off. I Can tell you that negative is over this side over here. 131 millivolts.

That's what we're getting before, right? That is not working. That is not like that's gotta be a power rail right? And look at this pin over here, right? that is going through an inductor like that's got to be like a power rail. Doesn't matter if we get the probes around the other way, right. Probe between there and there, there and there like you know, like something's got to be a power rail in here somewhere.

right? Even if you just you have no clue, you just randomly probe around at large traces with decoupling caps and large number of veers and stuff. right? There's just there's not. There's nothing. And I think the second one here.

Well, the second one here is red. There you go. 3.2 volts. So we get in our voltage in there.

But once again, this is over this part of the circuit. So is it. It's nowhere near that power up thing, so I don't know. We're just.

it's not getting through. There could be like a diode or in thing or something that activates that uh Power on latching circuit and bypasses that. Somehow there could be something tricky going on there. Um, and it's just not getting through.

So you know I wouldn't rule out that uh, transistor pair that we've got there. That might be a causing an issue in both the red regular power on function via the switch and also via the external programmer as well. That'd be just my luck wouldn't it bloody? Murphy right? So what I can say now is that the micro. You know, you can't say the micro is just door.

The micro is faulty. Let's just replace the micro. You can't do that. There's no voltage going to it, so of course it's not going to do anything.

Of course we're not going to get a clock like we couldn't measure before now. I've got to decide whether or not it's better to uh, trace the power here via the range switch or and the battery or via the external programming header here. I Don't know. I'm tempted to think the programming header, but Murphy will ensure whichever way I pick it's going to make it harder.

But Ultimately, I Think either way is going to lead to the same fault. Now, it's not like the processor or some other part like a shorted cap or something like that is shorting down the rail because we're measuring 3.2 volts on that rail. which if that's 3.2 volts is not getting to the processor in any way, then we need to know why that. That is what we need to fix here.

So let's start off by doing a sanity check of what what I know as the sister. Well, the initial system ground over here and the ground over on the thing. Yep, it's the same ground. So let's go from here and find out which pins is this one over here.

Once again, that's also ground. That's what I suspected, right? It's the negative of the cap there. It's right. everything's hunky-dory Don't know why that Cap's missing over there, right? But all this all this stuff here, right? This is grounds.

This is definitely the ground pin. This looks like a Power Pin because it's coming through an inductor. You usually would have the inductors in the positive uh, rail. So we've definitely got our correct ground pin.

but we're getting nothing. Come in from over here. and of course this is our 3.2 volt. Power Pin Right, we're getting nothing.

So obviously you know we're not going to have like a PCB break or something like that. That's like the most. It's It's not impossible, but it's the most unlikely scenario, right? So I'd say that uh yeah, there's some sort of um Power latching switching circuit and I don't think that the battery input is going to be connected to here? No, and it's not. So what we can safely do now.

I think is plug in because I you don't want to be probing with two probes. So I'm gonna plug in the ground and I'm going to reconnect the ground over to here so that I am hooked on. So now I can just probe with the single probe and go around because you know it's it's going to be a common ground for the processor if you're trying to debug the multimeter chip which is the one on the other side. That's when all bets are off.

That's when all the grounds are different and everything else right. and you're going to come a gutter if you're trying to do that. But this is just the processor, right? The ground is connected through to the battery and through to there and through to the processor. No worries, but the analog circuitry.

just be aware. Very different scenario. Okay, so let's check again. We have 3.3 volts.

What's that 3.2 before? Anyway, we're yeah. 3.3 volts coming in, right? So where is that pin going I'm going to have to flip it over. actually I will trace this. Ah, there we go.

There we go. It's that fatty. It's that fatty running off there. Let's run into that resistor.

there. Is it. Is that a zero? Ohm Resistor It is a zero Ohm resistor. So it's a jumper.

Okay, so yeah, we've got this fatty Trace going off here. Off here. it's going down here. Okay, hello, there we go.

4.5 volt bat. But it's not connected through to the battery. which is 2.2 That's interesting. Okay, so it comes over to here and it jumps up.

Uh, is it is it that via there? Yeah, there it is. Okay, so it's jumping up over there. Okay, so we've got two inputs here. Aha, this is now starting to make sense from a physical layout point of view.

Here's our battery input here. Okay, and here is our input for our external programmer, right? So we've got both and we can see that buggering off on the other side there. flippity doo da. What was it this one here? Uh, it's going on.

an internal layer bugger it. But yeah, it's around here. There's something I Reckon there's something in that power latching circuit. There's got to be That's the only thing that makes it that makes sense.

Uh-huh. Once again, there it is. Our 3.3 volt going into there, right? and it's not and it's not coming out. Exactly the same thing is going on here.

Exactly the same thing. You remember how it switched through before. So from there to there, that's how it was. uh, switching.

and this is just the uh, bass slash gate here. Maybe it's that puppy. I Think this is part of the latching circuit, but I think this is the main one that switches the power through to here. So I'm suspecting that little bad boy Q18, so we need to need a partner.

We need a definitive part number on that. Yeah, there you go. You get that. That is B0329.

Okay, so this is some form of soft latch power circuit. Where have we seen this before? Uh, check it out here. In my uh, extremely popular, uh, soft latch power Circuit video, we have a p-channel mosfet with an uh N Channel bipolar pulling uh, the gate down to ground and where you can have a third transistor over there do the latching function and stuff like that. But anyway, um, in that particular case, we'd have like the micro like doing that.

Yeah, this is the exact same Arrangement here now. I Couldn't find any info on this B0329, but I think that is a p-channel mosfet because it matches the pin out for a p-channel mosfet. So I've got a voltage coming in here to the source and then we've got the pull up resistor which goes through two of these like that. and then we've got this.

This would be an an N Channel bipolar transistor and that is just going to pull that down to ground. So and which is our ground is here. Yep, it does. So there you go.

So that is ground. so it's just simply latching that, uh, down to ground. No worries. I'm suspecting that because the bipolar transistors are more rugged than mosfets.

If you're going to have a transistor file out of these two, your money should be on the mosfet, which inside I'm just going to go to my mosfet kit, find a P-channel mosfet and I'm just going to replace that I Guess it takes two seconds. Wiggle wiggle wiggle. Yeah, come on, you can do it. Go on ski.

Okay, what I've got is a BSS 84. It's a small signal. Uh, P Channel Mosfet should do the business. Got our 3.3 volts coming in here.

Do we get our 3.3 No, we've come. Augusta That ain't it folks. You see now a problem here. Is that that transistor? Of course it's not going to switch on because that like that is not grounded.

So I should have actually checked that before. Maybe I was wrong. Maybe the end. Channel Now the interesting thing is, if this was a an Npn, a functional Npn bipolar, we should be able to measure the diode drop on the gate there the base emitter.

Because this is the emitter. this is the base and we ain't measuring anything there that's either not a a bipolar transistor or it's um, bugging. So that's an A603g and I can't find Once again, can't find any information on 0603 G Now what I've done is I've um compared to another unit because I have one. Sure enough, there's no Um Npn uh Junction in there.

So this is not a Bipolar I Think this is a mosfet. Get the multimeter back out. So what we expect is actually I've got the external power plugged in. We expect a positive signal on there and I've compared that with a good unit.

and yeah, we get 3.3 volts there. So the micros obviously like, you know, doing that and switching that on so a bit. it's not doing that. so I don't know that's going to be hard driven so we can't just short it out because then we'd be shorting out the output our gate.

but we could actually remove that resistor there and actually, um, you know, connect that to the input and that would latch on the circuit. Or of course, you know we could just bypass the main switch in mosfet here. um, switching that through. but yeah, I'm I've confirmed on a good unit that that's what that does.

You get a 3.3 volt signal on there that turns on this end Channel uh Joby here which then latches and pulls on the P channel here and switches the power through to here and I've I've confirmed that. so that's that's definitely what's going on. so it could still be a dead micro. The boot code in the micro is like put in that high somehow, so you'd have to follow the money there.

Once again, we could have saved three quarters of our time here if we actually had the schematic. Okay, at this point, I'm done screwing around with this thing. I'm going to short out the power transistor here and so I've removed that one I put in I'm just going to short there to there and that will permanently switch on the power to this thing and we'll see if the damn thing works. It's going to measure the voltage here.

No see, we still get nothing out of there so it's not latching that on. Let me try my uh, see if it can connect to the chip on my programmer here chip. ID from IC No, it's got no. I'm getting nothing.

Measure the voltage between there and there and that should be our 3.3 volts. There it is. see if we get that over here. 1.77 Let me compare a good unit.

Okay, so here is a good unit in uh, programming mode. You can see it's got the dashes across. here. it's switched the micro on.

Uh, it's in off position but we're powering it uh, through here and 3.3 no 1.6 and there is 3.3 Back to the bad board here: 3.25 Okay, right. so we've got the same conditions, so the jet let's just assume that's getting through to there right? So the chip is being powered okay and we're getting nothing on the programmer. Um, so whereas the programmer tells me the chip ID and it it works on the good board and doesn't work on this one. So the only other reason I can think of that this micro is, uh, not working apart from it failing is we go back to the mechanical side of things and a crystal.

Um, there it was there I Decided to remove the crystal because foes in uh, crystals are a thing. so they're a mechanical our part and unfortunately I lifted the pad. this is a real dog to get off I could not get this off properly with either hot air or with a dual soldering irons. It just lifted the whole pad off.

So unfortunately, um, yeah, that's a bit of a fail. You can see the Caps are on the bottom here and you can see they get there that they've got a 10 Meg resistor across there so unfortunately that's I'm gonna have to wire a mod wire into there around to there. The Uh 121 GW actually has the same except it's a through-hole and one of them is 4.9152 I can just Bunch that in just to try it and uh yeah, she'll be right there we go. And you've got to ask yourself, do you feel lucky? Well, do you punk those two holes there? Oh no fandom.

I Might be able to solder the crystal down to those two beers, but yeah, whatever. we got the right gauge. Why yes, I Do. look at that.

Oh yeah, all right, we'll just push that out of the way. I can just solder the crystal onto what's remaining of those of that pad. and that one. All right, we have a crystal bodged in there.

um I don't know what pad that's well, it's not even touching that pad. I Don't think or it might be slightly, but that's just the case if it's ground. Hey, if not, it probably doesn't matter. it'll oscillate.

Plug out programming header back in. Nope. still not reading the ID Still not reading the chip ID Oh so much for that. That was worth a try.

It's oscillator in. maybe there's nothing wrong with that Crystal at all. And yet the reason it wasn't oscillating before is because it wasn't getting power. Damn.

I Should have actually, um, re-checked the oscillator when we discovered that there was no power to the chip. I should have rechecked it after after we forced the power on. Yeah. I Just butchered that board for no reason.

Let that be a lesson to you. Oops. So yeah. I Had no trouble like I thought it'd be easy to get that Crystal out but it wasn't The adhesive on the bottom of the pad just gave away and bought.

Once that happens, you know it's like you can repair stuff like that. You could get some like adhesive copper and I could actually repair that uh pad perhaps. And you know if I was to do a proper uh repair on this, that's what I'd So yeah, you can see there that is oscillating just fine and dandy. It's not talking to the programmer so I can only presume.

yeah, the chip is dead, the internal oscillator is working, but something else has died. That's the only conclusion I can come to. Now please leave your thoughts and comments. uh, down below.

I'm going to leave it at that. Sorry, you know I know a lot of people don't like the unhappy ending, but there are a lot of people who think the journey is what matters and this has been quite a decent little journey we went on here. This sort of stuff doesn't take me long, by the way, if I'm not shooting a video it, it doesn't take me this long. I'm not yapping on I don't have a spare chip I Could you know even if I like I would have to rip one off another board and I don't have a junked R786 now I could get one from Bryman.

but then even if I did, that would prove that it was the chip. But uh, then it would lose its calibration values because I Don't believe there's an external E-square problem in here I Think it's all internal. it's in the protected mode of the chip the calibration values so you can reap, update the firmware and you don't reset the calibration values. But if you physically change the chip, yeah, um, you're going to lose some of the calibration values.

It might still be. Basically, you know it might still be within spec, but it's not going to be tweaked. I Think we've come down to the micro, but if you've got a better guess, I could go and Trace the signals for the programmer and stuff like that, but Ig's now we're getting fancy pantsy I don't even know the pin out anyway. I'm going to leave that as a part one.

so if you enjoyed that troubleshooting, Journey give it a big a thumbs up and as always, add discuss down below and over on the EV blog forum and thank you to all my patrons as well. I put the videos up first on the Patreon account. Um, in fact I put this one up as a partial one last night. like a 30 minute edit.

Um, original edit. Never intended to repair it I just thought you know I just started down the rabbit hole. thought it might be interesting and easy to see why it failed and I think yeah I think the micros just died and then it doesn't latch on. Yeah, we got carried away.

Uh, replaced in a few parts we shouldn't have there. but that's all part of, you know, troubleshooting with hindsight. Yeah, I you know I goofed a few things I'm trying to shoot a video at the same time and you know, trying to. Yeah, so that might have distracted me.

but yeah, I shouldn't have butchered that Crystal that was a bit mean. Anyway, you can also, uh, catch some exclusive videos which aren't on the YouTubes uh, they're over on my Odyssey Channel and I've got a new product right outside the door there. There's a whole bunch of new products. Um, that? I'll um, do an unboxing of that and I will like I haven't seen it yet I'll do an unboxing of that I'll Whack It On My Odyssey channel is an exclusive, so check that out if you want anyway.

catch you next time.