YAART reporting everything as an error

[Macross_VF1]

A few weeks ago I asked for help with an Atari 520STFM that was behaving strangely. It was suggested that it might have RAM problems so I asked around and got a disk with YAART (Yet Another Atari Ram Test) installed to test the machine.

The thing is though, while YAART seems to work as intended, it also report pretty much everything as an error. And that just can't be right, it's pretty much impossible that every RAM chip is faulty so it has to be something else, perhaps something that connects all the chips together and coordinate them?

I took a photo of the testing process which I have attached here, but you'll have to excuse the poor image quality, photographing an old CRT is bloody difficult.

Edited January 11, 2019 by Macross_VF1

[ParanoidLittleMan]

What 'coordinates' RAM is MMU chip. But should start with power supply. Replace it if can. Replace electrolyte capacitors in it.

[Macross_VF1]

What 'coordinates' RAM is MMU chip. But should start with power supply. Replace it if can. Replace electrolyte capacitors in it.

I have an Atari 1040 as well, would it be possible to switch power supplies between the units to test this theory or are they too different?

[snarkdluG]

You can switch the PSU to test. Even MMU chip can be switched to test if it is socketed.

[Macross_VF1]

You can switch the PSU to test. Even MMU chip can be switched to test if it is socketed.

Thanks for the confirmation on the PSU issue. However, I have no idea where the MMU is located or what it looks like. I suppose it differs depending on the revision of the motherboard?

[snarkdluG]

Thanks for the confirmation on the PSU issue. However, I have no idea where the MMU is located or what it looks like. I suppose it differs depending on the revision of the motherboard?

Should be labeled U56 on the silkscreen on the board next to the socket. Later revisions have surface mount chip soldered to the board. See different STfm revisions here.

[Macross_VF1]

Should be labeled U56 on the silkscreen on the board next to the socket. Later revisions have surface mount chip soldered to the board. See different STfm revisions here.

Thanks again! You wouldn't happen to know where the MMU might be located on an Atari 1040STE rev CA4003290?

[Macross_VF1]

No matter, I've just been told that it is a combined chip in the 1040.

Anyway, I've tried swapping the PSUs and it makes no difference. Is it possible to buy an MMU from somewhere or am I SOL?

Also, in order to pull a socketed MMU chip, you need some specialized tool, right?

Edited January 12, 2019 by Macross_VF1

[snarkdluG]

Also, in order to pull a socketed MMU chip, you need some specialized tool, right?

You don't have to, but it's easier. Use a small screwdriver or something similar hard tool. The pry the chip up with the screwdriver in the small slit on opposite end from each other, in the corners. Just pry a little each time. Do it equal amount on each end until it pops out. Don't just pry on one end. Otherwise you can use a plcc extractor like the black ones from ebay.