Top Loader issues

Hello everyone,
I'm not sure if this is the place to ask, so please forgive me.

I recently picked up a Top Loader. When plugged in the video output is a black screen, however, I can hear and even "play" games.

Upon opening up the console, I found evidence of a previous owner trying to AV mod the console. There was even a wire connecting a leg of the PPU to the board (removing it made no difference to the system's performance.).

What do you suggest I do? It seems that the previous owner messed up the mod so badly tha they couldn't repair it. Could I perhaps just replace some of the CPU or PPU with spares from a scrap front loader?

Thanks

If you're lucky, pin #21 on the PPU is just broken externally. Just reworking that with a relatively cool soldering iron should eventually coax it back to life.

If you're unlucky, they cooked it and the thermal stress sheared off the bond wire instead inside the epoxy package.

... regardless they clearly had no F_ing clue what they were doing, because PPU pin 30 (that green wire) isn't anything interesting ... unless they somehow tore up a trace and tried to bodge it back in.

Thanks for the reply
Is it irreparably damaged if the bond wire is messed up, or just REALLY difficult to repair?

I, uh... well, I guess pedantically it's repairable. If you had a friend with a wire bonding machine. I mean, it's ridiculous, but ... well, if you knew you had a friend with a wire bonding machine you wouldn't need to ask whether it was repairable.

I'd make sure there was no signal on pin #21 (just use a PA or stereo with line in and listen for a Very Loud 60 Hz buzz) before you give up on it.

If you have no way to get your money back, I'd try just finishing the AV mod. It's very common to sacrifice the RF output for a composite AV mod on a top loader, and I did so myself when modding mine.

You need a specific transistor for the amp in the mod, and while there are probably equivalents that are easier to come by, the one I found suggested was not easily available at my local electronics store, however the top loader already has one on its PCB used for its RF circuit, so I assume that it's very common to do what I did, and desolder that one from the board and use it in the new circuit for the AV amp.

It's been a while so I could be wrong, but I THINK it's the one labeled Q1:


You may also check out the three resisters labeled R1, R2 and R3 running along the copyright text next to that transistor. I think it's common to cut the traces to one or more of these when making video mods on the system.



As a final note, no one should ever play NES games via an RF signal. While composite itself is pretty horrible, RF is likely to call all sorts of eye cancer.

[citation needed]

With one exception: feeding the AV to a capture device while playing through RF. This way, you avoid the additional lag of playing through the capture device.

Also saves you the cost of a splitter.

[hyperboles]
I doubt I need citations to prove that RF video signals look awful. We all have eyes I don't understand why anyone would put up with it in 2017 when the immediate alternative is usually easier to get working, too.



I've been recording tons of NES footage through passive ~$0.5 splitter cables, it works just fine.
For the future though I'll be recording all my footage through RGB signals, which I've also been using passive splitters for. Not typically recommended because if you RGB modded your NES you probably care a lot more about the image quality, but to be honest I don't see any visible quality loss.

I actually kinda think the 2600 looks better with all the RF noise added relative to one that's modified for S-video...

If the pin is really broken and has no point you can solder it, you can try to use a micro emeryl or micro grinder and carrefully fray the the enclosure just above the pin.
Them a small piece of thin wire can be soldered easily and make a new terminal.
I tried my best to do a nice picture, but I think this shows what I did here:

Hope this helps if the worst happens.

With access to slightly better tools, you can do something like this instead of using a dremel.

Hah! And I thought I was being fancy scraping away at the package with a knife.

Wow! That's a lot more precise!
Can something like this be done on ceramic parts, like EPROMs?

Doing so will probably breach the frit seal on a ceramic part, but sure, you should be equally able to erode ceramic as epoxy with a CO₂ laser.

From my experience of repairing famiclones with discrete chips I can tell you that if there is sound but no video, the video amplyfying transistor needs to be replaced. Replace it with ordinary BC327/337/547/557 (can't remember if that's NPN or PNP). The one in console has definitely different pinout)

The 2SA937 in the PCB picture above is a relatively high gain non-darlington PNP transistor; any other similar transistor should be good too (e.g. BC856, BC857, BC858, BC807)