AV Famicom help

aha2940 · Jul 26, 2014

Hi

I recently got an AV Famicom on eBay. Was listed as not working, that's fine. When I got it, I noticed two things:

1. When powered on, all the voltages that should be +5V, are around +1V only. That made me think of the voltage regulator, but replaced it and same thing still happening.

2. When powered off, there is very little resistance (around 20 ohms) between ground and +5V. Is this normal?

I already tried removing most chips from the board (except for a custom Nintendo BU3266S chip and the VRAM chip which is stuck). Even with most chips out, all the symptoms persist.

Thanks for any pointers / help.

leonk · Jul 27, 2014

I would start at input and start working from there. Keep on moving component at a time till 5V drops to 1V

aha2940 · Jul 28, 2014

leonk said:
I would start at input and start working from there. Keep on moving component at a time till 5V drops to 1V

Thanks for the suggestion man, I tried that and got this:
- With the famicom connected but powered off, I get +10V (the output of the adapter) until the on/off switch, which is even before the 7805 power regulator. From the switch onwards, there is no voltage anywhere.
- With the famicom turned on, I get +1V before the power regulator (which got +10 with the famicom powered off) and after the voltage regulator I get almost no voltage. My multimeter is not digital but analog so I can see the needle moves a bit, but I can't get the exact value, however I get way less than a volt after the 7805.

Does this help figure out the issue? I am thinking a short circuit somewhere, but not sure where it may be.

Thanks!!

Yodd · Jul 28, 2014

Do you have another power supply you can test the AV Fami with?

This sounds a lot like a PSU that fails once under a load.

you could also feed +5v into the system right after the voltage regulator to see if the system powers on.

aha2940 · Jul 28, 2014

broken said:
Do you have another power supply you can test the AV Fami with?

This sounds a lot like a PSU that fails once under a load.

you could also feed +5v into the system right after the voltage regulator to see if the system powers on.

Hi

I did this same test with my Sega Genesis Model 1 adapter (9V, 1.2A), and the results are almost the same, this time instead of +1V, I am getting +2V and a warm adapter. The first adapter I was using is a 10V 850mA I use to power my famiclone, and that works fine.

Thanks!!

Pasky · Jul 28, 2014

Best to start by providing a picture of the PCB, top and bottom to try and spot any obvious issues.

aha2940 · Jul 28, 2014

Pasky said:
Best to start by providing a picture of the PCB, top and bottom to try and spot any obvious issues.

You are right, here are some pics I took of the board. notice that here almost all the chips have already been removed and socketed by me, but the problem was the same when I received the board, with all chips in place.

Thanks!!

Pasky · Jul 28, 2014

When you do a continuity test between a 5V point (pin 40 PPU), and a GND point (PIN 20 PPU), do you have continuity? That should tell you if a short is present, if it's reaching that point. I don't see any obvious problems with the board.

aha2940 · Jul 28, 2014

Pasky said:
When you do a continuity test between a 5V point (pin 40 PPU), and a GND point (PIN 20 PPU), do you have continuity? That should tell you if a short is present, if it's reaching that point. I don't see any obvious problems with the board.

Yes, there are about 20 ohms resistance between 5V and ground when the board is powered off and disconnected. I am not sure if that's normal or the sign of the problem.

Thanks!!

Pasky · Jul 28, 2014

20 ohms sounds way too low. I dont have a AV famicom board to compare in front of me at the moment. But I do happen to have a US top loader pcb with the ppu removed, and checking 20 vs 40 gives me about 600 Ohms of resistance. You definitely have a short somewhere. It might be inside the actual DC jack.

Also, you are using a Negative center power adapter right?

aha2940 · Jul 28, 2014

Pasky said:
20 ohms sounds way too low. I dont have a AV famicom board to compare in front of me at the moment. But I do happen to have a US top loader pcb with the ppu removed, and checking 20 vs 40 gives me about 600 Ohms of resistance. You definitely have a short somewhere. It might be inside the actual DC jack.

Also, you are using a Negative center power adapter right?

yep, sounds like there is a short somewhere

I only hope the broken part is not that custom Nintendo JIO chip, because that's the only part that is impossible to find if not in another AV Famicom. I have spare CPUs and PPUs, RAM chips and so, but not JIO chips. And yes, both my famiclone adapter and Sega genesis adapter are negative center so they should be fine.

Thanks!!

Pasky · Jul 28, 2014

Out of the 15 or so damaged AV famicoms I've repaired. I've never had that chip go bad. It could be bad, but very unlikely. Try checking the power switch/reset circuitry next.

leonk · Jul 30, 2014

What is that Nintendo J10 chip anyways??

aha2940 · Jul 30, 2014

leonk said:
What is that Nintendo J10 chip anyways??

From what I've read, it seems to manage the controllers and some video functions, however there is very little info on the web about this chip (or I am not searching correctly)

Regards.

aha2940 · Aug 2, 2014

Hi

I managed to fix the AV famicom, it works great now. What I did (after removing and socketing every single chip on the board) was replacing again the 7805. Bingo! for whatever reason the replacement 7805 I had put before was also dead (altough it worked fine when I tested it some months ago). Log story short: I now have a very beautiful 99.95 jailbar-free AV famicom working:

AV Famicom help

aha2940

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leonk

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aha2940

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