UPDATE FIXED Diagnosing a Famicom video issue, bad VRAM?
Recently I purchased a pretty much exact copy of a famicom (famiclone) off ebay and upon receiving it (described as working, LOL) it was missing the CPU and PPU but luckily had the slots to allow chips to be added. I used heat gun to remove chips from old NES board and put them in since the board was marked with same chip #'s (board is same as famicom too). The RF board ribbon cable was loose & I wasn't sure it was even complete since it appeard to be missing a few components but I soldered ribbon cable back & did a channel search and got an image at 14 and 3 but 3 was the one that worked best. I popped in super mario 3 & the sprites at the intro are fine like Mario, Luigi, the falling Leaf, the Koopas. But the background is garbled. Audio seems to be fine as well so at first I thought the PPU might be a problem & pulled it and clean and bent connectors and popped it back in but with same result. I got thinking since the sprites seem ok possibly it's a ram issue especially if one ram chip is more for background and 1 is allocated for sprite data. The background scrolls but the image is just missing parts, garbled, with letters and numbers so has anyone had an issue with VRAM going bad in either the NES or Famicom? I'm going to use heat gun to remove the Vram from the old NES board & there is a bit of a problem there because it's half the width of the one in the famicom. Seems the NES early units had the larger ram since the motherboard mark for it is larger but by 1987 the date of my NES board apparently they'd went with a smaller ram chip. Could I simple remove it and leave the suspected bad VRAM in the famicom & solder the smaller chip to the legs of the original using wire on one side or would I need to pull the old Vram? Any ideas on what would be best method here or a link to buy a replacement that's the same size? Also, anygood way to test the Vram before removing it? Pressing on the chip seems to not change anything and it don't get hot as I've seen many others say is a sign of bad vram but then again none of the chips pressing does anything nor are they getting overly hot. Nothing about the RF could cause this I assume since the image and colors is crisp and clean just garbled. I appreciate any help or info anyone could provide.
Haha fixed the Nintendo famicom famiclone that ebay seller screwed me over on ($70 invested insisted it worked & it was missing CPU, PPU, Power board connector broke, LOL) seller offered me full refund for return but after lying say he personally tested it I was no way sending it back so I chalked it up as a lost and was determined to fix it because it's the best copy of a famicom I've ever seen. I'm no electronics expert by far but used a bit of common sense to figure this out after reading about how the NES gathers sprite and mapper date from PPU and the VRAM. Sprites worked fine the background stuff was garbled. Audio worked as well. I took CPU and PPU from old NES board and installed & was getting the bad images like 1st ones shown. I realized that whoever had robbed the original CPU and PPU probably had encountered the issue and gave up on it so it made sense that the ones I installed was most likely good. So VRAM was the next thing I figured to install. I took the VRAM from the old NES board using a heat gun and started trying to remove the old VRAM from the famiclone with the same method but foil didn't help much and components got far too hot so I went with the long hard method of cutting chip out & tediously desoldering and using solder pump to clear each chip leg & solder. Needless to say it took a while but a few hours later I had the new smaller in size ram chip installed (whopping 2 KB) & fingers crossed fired it up and my common sense proved not to fail me. Games work great & although I have a lot invested I'm happy to have a really nice original famiclone from late 80's time period that even the most dedicated nintendo enthusiast would have trouble seeing the subtle differences. I can't believe they actually got away with making them so exact & have to wonder if they & Nintendo did not have some sort of deal.
Haha fixed the Nintendo famicom famiclone that ebay seller screwed me over on ($70 invested insisted it worked & it was missing CPU, PPU, Power board connector broke, LOL) seller offered me full refund for return but after lying say he personally tested it I was no way sending it back so I chalked it up as a lost and was determined to fix it because it's the best copy of a famicom I've ever seen. I'm no electronics expert by far but used a bit of common sense to figure this out after reading about how the NES gathers sprite and mapper date from PPU and the VRAM. Sprites worked fine the background stuff was garbled. Audio worked as well. I took CPU and PPU from old NES board and installed & was getting the bad images like 1st ones shown. I realized that whoever had robbed the original CPU and PPU probably had encountered the issue and gave up on it so it made sense that the ones I installed was most likely good. So VRAM was the next thing I figured to install. I took the VRAM from the old NES board using a heat gun and started trying to remove the old VRAM from the famiclone with the same method but foil didn't help much and components got far too hot so I went with the long hard method of cutting chip out & tediously desoldering and using solder pump to clear each chip leg & solder. Needless to say it took a while but a few hours later I had the new smaller in size ram chip installed (whopping 2 KB) & fingers crossed fired it up and my common sense proved not to fail me. Games work great & although I have a lot invested I'm happy to have a really nice original famiclone from late 80's time period that even the most dedicated nintendo enthusiast would have trouble seeing the subtle differences. I can't believe they actually got away with making them so exact & have to wonder if they & Nintendo did not have some sort of deal.
Comments
Could also be bad PPU or PPU RAM, but your description kinda sounds like the same thing dirty pins can cause.
I would also suggest checking continuity from each of the CHR ROM pins in the cart connector to wherever the traces are supposed to lead on the NES board (probably PPU legs or PPU RAM legs).
Think it could be the CHR pins of the cartridge connector?
Could also be bad PPU or PPU RAM, but your description kinda sounds like the same thing dirty pins can cause.
I would also suggest checking continuity from each of the CHR ROM pins in the cart connector to wherever the traces are supposed to lead on the NES board (probably PPU legs or PPU RAM legs).
Thanks. Since I get the same image each and every time with the sprites working on mario 3 intro screen and no amount of fiddling with cart changes anything I've convinced myself it's bad VRam. Just in case Mario 3 has those loaded from onboard memory I tried Super Mario Bros and the sprites on it's intro was shown as well it was the background that was all messed up & it's weird because it seemed to actually have some of the Mario 3 background stuff showing but so garbled hard to tell I just don't recall super mario bros having the colors that was showing up as the ones in Super Mario 3. I would have thought cutting the power would have deleted everything on the ram chips & ppu but maybe not? CHR pins I'll have to lookup to see what those are & do more reasearch there but connector and traces all look good from appearence at least. I wish this ram chip from my parts NES was the same size because it's going to make switching it out much more time involved.
I've hear of people identifying faulty Atari 800XL RAM chips with "the piggyback method" where they put one chip over the other and essentially connect both temporarily. I don't know if that would work here but you can google "Atari 800XL piggyback RAM" and see if that helps.
PPU could have been cooked by the heat gun but bad RAM is still a good possibility. Obviously, someone socketed and removed the Original CPU/PPU for some reason and having something else wrong on the board fits that.
I've hear of people identifying faulty Atari 800XL RAM chips with "the piggyback method" where they put one chip over the other and essentially connect both temporarily. I don't know if that would work here but you can google "Atari 800XL piggyback RAM" and see if that helps.
I think this board was socketed to begin with after getting some other famiclones opened up and seeing most are socketed. As you said I believe there was a problem so they simply robbed the cpu and ppu out because they never figured out or tried to repair it. I have removed the U4 Vram from the NES board using the heat gun & I'm happy to see the famiclone board as the spot to accept the smaller ram module as well (row of solder pins in the middle of the larger width vram) and the VRAM in the system seems not to be of any name brand or not even made in Japan like the other chips. I heated the PPU and CPU from the bottom of the board and it didn't really get too hot for too long actually I don't think it would be any different than heating with soldering iron to remove each pin at a time and I'd read about another guy who uses a heatgun with great success on doing these chip removals. Anyways, here's pics of the image I'm getting. I used rubbing alcohol and toothbrush to clean the board good and metal polishing pasted before using another round of alcohol to clean it all up and scraped a bit of the solder flux (dark yellow or brown substance almost like glue) off around a few pins under the VRAM. I'm going to plug the PPU back in (I brushed it's slot connector out too) and try it again and possibly remove another PPU from another NES board to try before tackling the VRAM but then again maybe I'll go straight to VRAM I just don't think the PPU is bad with what I'm getting on screen but I could be wrong. I might do as you said and try to piggyback the ram once I read up on it that would be easier and less extreme on the board trying to remove the old ram. I saw where a girl actually used a much larger 128 kb ram chip on a NES board with video problems and fixed it so I'm thinking piggyback should work but I guess it all depends on if the NES will bypass the bad ram area and go to the piggyback one I think it would require a hardware programmer to understand if it would work or not. Thanks for the info everyone and keep it rolling in because this will possibly help other NES and Famicom units get repaired since info is pretty scarce on this seem like after hours of searching the web.
PPU could have been cooked by the heat gun but bad RAM is still a good possibility. Obviously, someone socketed and removed the Original CPU/PPU for some reason and having something else wrong on the board fits that.
I've hear of people identifying faulty Atari 800XL RAM chips with "the piggyback method" where they put one chip over the other and essentially connect both temporarily. I don't know if that would work here but you can google "Atari 800XL piggyback RAM" and see if that helps.
I got it repaired updated topic with how. I hope this helps others & I appreciate everyone's input I want to get this repair out there before I've seen a lot of others with same issue with sprites working but not background but never found any definite fixes with pics showing they got it repaired. They just all dead ended so I'm thinking this would help several others save that old NES or Famicom that has a similar issue.