MV1B 5v to ground short (and stereo Mod wire running from OPAMP1 to IC4)?

[Kujako]

Another broken MV1B on my workbench. This one with a third party NeoBIOS Masta that I think is the problem (lots of hot glue trying to hold it down @Neo-Alec here's an example of what I often see) but it also has a stereo mod with a detached wire. I've seen this before (example) but I have no idea what it's supposed to do... I am assuming it's supposed to go to IC4 as the example shows, but why?



Edit: And now there seems to be a short between 5v and ground. I did get it to boot to the cross hatch at one point, but now it's dead. I've stripped all the modifications other than the battery holder (charging circuit is disabled and there is no short at the battery). Without the cart reader PCB, every single capacitor and +5v/Ground pad is shorted. Going to remove the old disabled BIOS and see if that's it, otherwise I'm stumped. 12v seems fine.

 

[Neo-Alec]

Yeah, modders glue down the NESRGB the same way. I don't think it helps. It just makes a mess.

IC4 is the synthesizer itself. You shouldn't need to wire anything there. The wire in your example looks like a repair for a trace the modder probably burnt up.

I think the loose wire you're talking about is the one that goes to A50 on the cart board connector? JNX's guide:

https://www.jamma-nation-x.com/jammax/tutorials.html?show=mv1bstereo

 

[Kujako]

I think the loose wire you're talking about is the one that goes to A50 on the cart board connector? JNX's guide:

https://www.jamma-nation-x.com/jammax/tutorials.html?show=mv1bstereo

No that's the blue wire running to "C" on the amp. The disconnected red wire is on pin 4 of the 844G which should be VCC. It was clearly intentionally lifted, no clue why so not sure where to reattach the line. In the example image I see a similar wire, so I'm assuming there's a reason for it (shrug).

If they were trying to repair the lifted pin they'd run it to the capacitor it would otherwise connect to. But I see no sign of that. Looking again, the loose end of the wire isn't tinned. So maybe they lifted the pin to disable the mono amp and added the wire in case someone wanted to restore it? No clue...

 

[Neo-Alec]

Okay. In that case I would probably just ignore whatever they did, probably remove the extra wire, and just make sure the mod is wired as it should be.

 

[Kujako]

Okay. In that case I would probably just ignore whatever they did, probably remove the extra wire, and just make sure the mod is wired as it should be.

Yeah, going to repair what I can see and then see if I get stereo out of it. Got it to boot to the cross hatch screen, so that's something. Also just now noticing that the top NEO-BUF is bypassed. Should be fine but I'll get that under the microscope to make sure.

Edit: and now there's a short between the +5v and ground on the jamma connector...

 

[Kujako]

Short isn't on the BIOS. Was a long shot, but thought I'd pull it off and confirm. Next I guess I can pull all the capacitors... unless someone has a better idea I'm at the "start removing components until the short goes away" stage.

 

[Kujako]

Short is gone! Removed AC11 (470uf 16v) and that seems to have been the problem. Also removed the amp chip (with minor heat released damage done to CN4) and battery holder before I got to the capacitor. But first capacitor I tried seems to have been the problem. Although the capacitor tests OK... but I'll replace it and see how things look.

 

[Kujako]

And the short returns after replacing the capacitor. Which means it's one of the ICs in the area (NEO-SDR-T?). So this may be a lost cause.

Edit: not the SDR. So think this goes into the parts pile.. bummer.