Technical and Repair Assistance

[MattyD]

Hello guys, I'm after a bit of info to help out someone on another forum.

He's just received an AV modded Fami and upon switching it on it blew up. He opened it up and said the wire connecting to the RCA jack for the video output had come loose and by the sounds of it, it's touched something it shouldn't have and caused a short.

He provided this picture which shows a component, possibly a voltage regulator, which has clearly been blown as there's a big hole in it 



I don't think my Fami has the same model board as this and was wondering if anyone knows either the part number or a suitable replacement so he can replace the blown part? Thanks in advance.

[ericj]

It's a voltage regulator, # 7805. 

[Thrillo]

I just bought an AV Famicom and it appears to work fine, except that the screen image it produces is rather dark. I compared it to my NES (connected via composite of course) and to my surprise, the NES produces a much better image: its brighter and sharper.
What's odd is that I believe my previous AV Famicom had a perfect image (it got lost in the mail). Could the change in brightness be due to a PPU revision? Mine is RP2C02H-0. Are there any resistors in the video circuit that I could check?

On a related note, my Twin Famicom's video has the "jailbar lines" issue that plagues NES 2s. I found a pot in there that increased the brightness, but didn't fix the lines. Wish my AV Famicom had that pot...

[133MHz]

The AV out connector or the cable could have rusted pins, which create electrical resistance, raise the impedance and darken the picture.

Oh and BTW, an AV Famicom will always look darker on a US TV set, due to the differences in NTSC-J vs NTSC-M.

[Thrillo]

The AV out connector or the cable could have rusted pins, which create electrical resistance, raise the impedance and darken the picture.

Oh and BTW, an AV Famicom will always look darker on a US TV set, due to the differences in NTSC-J vs NTSC-M.

Yeah, at first I thought that it was simply that obscure NTSC-J difference, but the difference in brightness and video quality is like comparing RF to S-Video, so there's something else going on. Increasing the brightness or contrast on the TV doesn't make any improvements.

I hacked a spare RCA cable in two, looked up the Famicom's AV pinout, and stuck it on the composite/ground pins and the image still looks the same. Is it possible that there's some sort of cap or resistor in the head of the cable that could have gone bad?

[133MHz]

Is it possible that there's some sort of cap or resistor in the head of the cable that could have gone bad?

Yes indeed. You'd have to check the transistor, caps and resistors which amplify the composite video signal from the Famicom's PPU chip. Unfortunately I don't have the AV Famicom schematic, nor do I own one to trace it myself. You'd have to follow all the way from the Video Out pin on the PPU to the AV out on the back, checking for components drifted in value.

[xyzzy32]

Those "jailbar" lines... are those normal for a famicom? Both the A/V mod and normal RF output on my original famicom have these, but not my NES...

[Thrillo]

Hmm, I guess I'll have to trace the path. I'm glad that the AV Famicom has a pretty simple PCB compared to the other models.

Those "jailbar" lines... are those normal for a famicom? Both the A/V mod and normal RF output on my original famicom have these, but not my NES...

I have three old style Famicoms and all of them have that issue to some extent. I even had a NES that was barely starting to show them, but then I fried the board and that was the end of that.

[133MHz]

Sounds like an electrolytic capacitor drying up.

[Thrillo]

Looks like the TV I was originally using has issues. I tried the AV Famicom and NES on another, older TV and the AV Fami ended up looking better on it: there was less ghosting between dark and light areas, such as the floor in SMB3's title screen, and the colors were more vivid.
Apparently my TV is very picky about composite resistance values. Doesn't surprise me because it also has video noise in the S-video input...

[133MHz]

Replace the decoupling capacitors right after the video inputs on your TV. Maybe they're dried up and they're allowing some DC offset to pass through.

If you're more experienced, check for good filtering on the B+ line.

[JC]

I've got a multicart that looks like this:





Any solutions? It's not quite as bad as my last posting, as I can make out the menu screen, etc. but it's quite broken. Tried cleaning the contacts and lining up the contacts various ways...didn't work.

[133MHz]

One or many of the very fine traces which connect the chips (or gloptops) to the cart edge could be severed. Check them and repair if necessary.

The cart could have a shorted address or data line (blown input protection circuitry). Check for continuity between all address and data pins. If you find a low resistance (say, 100 ohms or less), it may be possible to resuscitate the cart by trying to blow up the short with a power supply.

[Lorfarius]

Not a good sign but I turned my Twin Famicom on this morning and nothings happening  No red light flickering and cant get anything out to the TV. Any suggestions folks?

[133MHz]

Try another AC adapter first.