Grey screen of death

Started by zmaster18, April 17, 2016, 06:50:51 am

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zmaster18

I have 3 Famicoms that display a grey screen, and I have cleaned the cartridge slot a million times by the way. I've read elsewhere that it might be the CPU is defective. Is there any fix for this? I don't think there is, since people call this the "grey screen of death". Just wondering if there's anything that I can do

And yes, i reflowed the solder on the cartridge slot and all chips.

jpx72

I am afraid you won't find out untill you swap the relevant chips for known working ones and try. Or you need to check out sinals with osciloscope.

zmaster18

All I have to test with is a multimeter. Which points of the CPU or PPU should I test? I have the nesdev documentation for pinouts.

HVC-Man

Gray screen just means the CPU isn't booting data from the PRG ROM chip on the cartridge. The PPU has nothing to do with the gray screen.

If the cartridge slot isn't the problem, then you'll want to check the SRAM at U1, 74LS139 at U3 and the 2A03 at U6.

A multimeter is of little use here, you'd need a logic probe or oscilloscope to check the activity of the chips involved. You'd only need a multimeter if the board was damaged or corroded, thus causing address/data lines to go dead.

The 2A03 rarely goes bad, but it has been documented before. More often it's the off the shelf parts that die first. If you don't have a logic probe, you could just buy a new 16Kbit SRAM of a similar speed, another 74LS139 logic chip and swap them for the old ones.

In the event you do have a logic probe, what you'd want is to get the datasheets for 74LS139 and 16Kbit SRAM and use that to check the I/O of those chips. Address lines should pulse at the very least. If any address/data lines are stuck high or are otherwise dead, then either a trace is bad somewhere or one of the chips involved has developed a bad I/O signal.

zmaster18

I guess the only thing I would try is desolder the SRAM chips off of some other junk board that I know had functioned before and put it in.

Taking a look at 2 of these faulty boards, the U1 chip looks damaged. One of them has 2 kinda corroded legs, the other board has 3 extremely rusty legs. These legs are the ones closest to the cartridge connector. The U3 and CPU look fine for both boards.

These boards are CPU-07 by the way.

famifan


Arkanix38

Fairly sure he lists his broken consoles as broken. Bought my fami from him as a side project and got it running after a little troubleshooting.

zmaster18

April 20, 2016, 10:53:45 am #7 Last Edit: April 20, 2016, 12:20:39 pm by zmaster18
Quote from: Arkanix38 on April 20, 2016, 06:25:34 am
Fairly sure he lists his broken consoles as broken. Bought my fami from him as a side project and got it running after a little troubleshooting.

They were listed as defective. In the past, the defective systems were easily fixable, but lately I've been having really bad luck. I'm never buying a defective one ever again. This is just too much trouble.

I managed to desolder some SRAM and CPU chips, but I need to buy some sockets to put them back on the board. It is really hard to align the pins of the chips back into the holes.

Post Merge: April 20, 2016, 12:20:39 pm

So I took out the totally rusted SRAM chip out and put another one back in. Still doesn't work. It looks like there's some damaged traces around the U1 chip... It's really hard to see where they go since the traces run under the chips and cartridge slot. It's way too time consuming to check everything, so this board is toast. :(

HVC-Man

Don't put chip sockets in an original Famicom, they get in the way of the eject lever.

Yeah, I don't know what kind of wars or holes in the ground those Famicoms have been through, but they take the cake for most beat up Japanese imports ever.

You may want to desolder the CPU and PPU from that board, nice to have spare parts assuming they work.

zmaster18

I've found that defective Famicom boards usually involve broken traces, almost always in between the cartridge connector and the RAM chips. I now have 10 junk Famicom boards :(  I'm going to see which ones have the best condition traces and replace the chips on those. Maybe if I'm lucky I can get 1 to work again.

I will take off all the chips and save them for people who need them. I'm going to get some sockets and make a special Famicom board just for testing chips.