Sharp Twin Famicom Patchy/Blocky video signal fix repair

Holy-SNESHoly-SNES
in Help Wanted!
I have a Sharp Twin Famicom (the black with red) which has some sort of video problem.

This is the first Twin I've owned so I know didly squat about them or how to repair them.

I'm using the standard AV ports and my cables are good.

I don't have the official power supply so just using a DC 9V 2A transformer.



When I turn it on, the sound is perfect. The picture however comes up all blocky and patchy.

Looks like the different colours or whatever... I'll just post the pics.

You can actually play it so it works in that sense. Tetris blocks appear and rotate like normal (different colour though), just can't see anything else but the block lol.

If anyone knows what this problem is I would love to hear.

I can change things like caps, chips etc. so I'm not really limited in how far I can go with repairing it.



Main Menu (without cart). It scrolls too so it's not just a still image.











SMB/DH cart...











Some random pirate cart...



Comments

  • RetroHackerRetroHacker
    Looks like bad PPU RAM. The PPU has it's own 2kb RAM chip.



    Now, ordinarily I'd say that it was a dirty cartridge slot (bad connections to CHR ROM can look about like that), but since it does it in the menu, without a cartridge, then it has to be something internal.



    -Ian
  • NESHomebrewNESHomebrew
    I thought Famicom's were really picky about power supplies?
  • RetroHackerRetroHacker

    Originally posted by: WhatULive4



    I thought Famicom's were really picky about power supplies?

    Nope. Shouldn't be. I mean, I've never been inside a Twin Famicom, but if it's anything like the Famicom and the NES, it'll be the basic 7805 voltage regulator circuit. Linear regulator on a heat sink, capacitor. That's about it. It'll take any voltage with it's spec (between 7 and 35 volts or so) and regulate it to 5v. Of course, the higher the input voltage, the more heat it generates, so you should stick to something reasonable.



    Now, one difference between the Famicom and the NES is that the NES has rectifier diode in it, and it's original power supply supplied 9 volts AC. You CANNOT use the American NES power supply on the Famicom. You'll damage it. You need DC - the original Famicom uses center negative, and happily works on a Sega Genesis Model 1 power supply.



    In short, 9vDC should be just fine. If you want to double check you're getting good power, check the voltage at any of the major chips, or bypass caps on the board. It should be 5 volts.



    -Ian
  • Holy-SNESHoly-SNES
    Thanks for the reply's.

    Yes someone else mentioned it may be a bad PPU.

    This guy posted a vid where he swaps the PPU with a doner NES PPU...







    I'm happy to give this a shot but don't want to go through the hassles if it is actually something else.

    If there's any other explanation other then a fault PPU that would be so much easier.

    If this is 100% the issue then yeah.. I guess I'll have to start soldering.

    Can anyone else comment?
  • ulasamosaulasamosa
    its either CPU, PPu, or RAM, not much else to go bad unless its been tempered with previously and someone else damaged it

  • removed04092017removed04092017
    I'd clean the systems connector and games first. The lines on the screen are from the cart not making a good connection, and since they aren't in every example you know something is wrong on the cart side. And the sprites are also glitched, that's a good sign it's the connector too. PPU RAM being bad would mean nametables would be wonky. OAM being killed would probably result in garbage sprites everywhere, so the fact that they're being displayed correctly also shows OAM is probably good. I don't think it's a PPU problem.
  • WickedWonkaWickedWonka
    A friend of brought me her NES a while back and it was having the same issues. I removed the 72 pin and where the connectors are on the board, one of them was damaged. (silver at both ends but not in the middle, sorry, not good with technical terms) After trying the new 72 pin, same result. Removed it again, laid a piece of thin solder across the bad connection and tacked both ends where there was still silver. Melted the center making a bridge across the damaged area. It was a thicker but stayed on when the pin connector was put back on. Has worked perfectly since. May not be your issue but worth a look.
  • RetroHackerRetroHacker
    Guys, remember, it does this with no game inserted... That one screenshot is from the disk menu. It's not the connector.



    -Ian
  • Holy-SNESHoly-SNES
    Thanks for the reply's again.

    It is 100% not the connector or the pins on the cart.

    Like retrohacker says, it does this on the main menu, not just with the game carts.

    The 2 games you see are both on the same random pirate cart.

    I have an official Jap Tetris cart (who doesn't) which hasn't the lines down the screen but the image is all messed up.

    Like a said, the Tetris blocks appear (looking the wrong colour might I add) and move as normal.

    Most of the background is missing or come up in squarish patches here and there.

    I'm leaning towards one of the chips (prob PPU) but just want to wait for a few more answers or confirmation before I start working on it.

    Thanks again, everyone has been helpful
  • RetroHackerRetroHacker
    Which is why I'm leaning towards the PPU RAM, or even the PPU itself. If it was the CPU or the main RAM, then the games wouldn't play at all.



    -Ian
  • GuntzGuntz
    You could try using a logic probe on the PPU and associated RAM to see if they're acting odd, but I guess you'd need a working PPU and RAM to compare against.



    If you don't have a logic probe, you could try replacing the RAM first. If that doesn't solve the issue, try the PPU next.



    But before we replace components, open the Twin Famicom up and take some pictures. Maybe somebody has been in there before and damaged the system.
  • T3rraT3rra
    Make sure you give the PPU and Ram a good cleaning first. Corrosion on pins can cause shorts.



    Other than that, solder away.
  • RetroHackerRetroHacker
    A logic probe would tell you if you have a stuck data/address line or something. But RAM can fail in such a way that it causes a data line to become stuck at one state, which would load down the bus - it would be impossible to tell if it was the PPU or the RAM chip with the stuck output.



    Personally, I'd probably just start by replacing the PPU RAM, and if that doesn't fix it, the PPU. Why? Because the RAM is a smaller chip and changing it would be faster. Hehe.



    Either way, even replacing both chips shouldn't take more than an hour. And the parts are readily available.



    But I agree, carefully examine the board first before replacing any components. There could be some kind of physical damage, a short, or something. For instance, a bit of conductive material shorting out two pins in the cartridge slot, or pins of a chip. I've definitely found coins in consoles before. Or a gouged or corroded trace.



    -Ian
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