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Re: Wang PC260 issues.

PostPosted: Fri Jul 11, 2014 3:04 pm
by Clym5
Thanks for the link!

None of them seem to be hotter than the others, though they do seem to run warmer than I'd expect.

I removed the battery. It was 0.00v, but no leakage, nor corrosion anywhere. It was attached to the case, above the RAM.

I get one intermittent error, but I can't recall what it is. I'll check when I get home.

I'll have a good go at it tonight with my scope too.

Also, did you want that MFM ISA controller card?

EDIT: According to the beep codes, some chips, while piggybacked on the 2nd chip in the top row of bank 0 cause "Bit 6 1st 64K RAM failure" and on the 3rd chip "1st 64K RAM chip or data line failure multi-bit" and on the 4th chip "Bit 5 1st 64K RAM failure"

Is it safe to assume that the piggybacking chip has failed?

My scope's probes are shot, some break in the coax maybe. Wont be able to use it in the meantime.

Re: Wang PC260 issues.

PostPosted: Fri Jul 11, 2014 4:37 pm
by Clym5
Well, looks like something else went wrong. Can't boot now. I get a beep code, and no video. The error is "Bit 4 1st 64K RAM failure" Do you have any specsheets or something for these chips? Can't find much about them online.

Unless I can get some replacement RAM, looks like I'll have to put it away for a while. Unless I want a FM radio jammer, this thing kills all radio when it boots. Are there any ways to test the RAM ICs?

EDIT: By piggybacking a chip from back 1 to bank 0, I've got video. But no boot, and some missing text from the first screen.

EDIT2: I got bored, and piggybacked 2 chips on top of the suspect bank 0 chip, and the Wang came back to life! Still 256k, but booting!

EDIT3: Annnnddd, it's gone again. I'll stop using it for the mean time. The error for this hour is "Bit A 1st 64K RAM failure" No amount of piggybacking has saved it this time.
Done some looking into that error, and here's what I found. "64KB RAM failure: Bit 10; This data bit on the first RAM IC has failed. Replace the IC if possible" Would that mean the first chip in bank 0 is the culprit here? Sorry about all the clueless questions! Fair way out of what I usually do here.

Scope lives again too. Nothing I own works properly..

More EDIT: Got some more info on the RAM used in this Wang. It's a AAA2801P-07. Page operation mode, 70ns. Does anyone have some spare?

Re: Wang PC260 issues.

PostPosted: Sat Jul 12, 2014 8:38 am
by SpidersWeb
I'm think it's just a special version of the 41256 or 44256 style chips - 70ns, might be worth comparing the pinouts / features and seeing if there is anything special or not. It's certainly not a model number I recognise.
It's usually 41256 or 44256 you find in them - 256kbit x 1 DRAM. These can be purchased off ebay etc in bulk pretty cheaply.

But I couldn't 100% guarantee that'll fix the issue. My suspicions are that it's likely one of:

- chips failing
- noise on power lines causing something weird to happen (caps etc) (this is a theory I haven't tested yet)
- bad solder join(s)

For finding bad chips I was going to recommend diagnostics ROMs (require no RAM to boot, identify failing bits, and continually RAM test) however that would require a CGA or MDA display setup - no VGA support :(
I guess you somewhat have this already with the beep codes though.

MFM controller - I just looked up the sub model, yes! I'd be keen on that and the cables, happy to trade for stuff when you need it.

Re: Wang PC260 issues.

PostPosted: Sat Jul 12, 2014 10:19 am
by Clym5
Thanks for the info on the RAM.

I had a poke with my scope, and saw that when the speaker beeped out the error, there was a fair amount of the noise from that across 3 or 4 of the pins. Is that supposed to happen?

Also, on some of the chips, there are spots of rust where the pin joins the plastic, I saw one of Tezza's computers had this, but I can't recall if it had actually damaged the chip.

I don't have a CGA or MDA card, or monitor sadly.

I'll Pm you later today about the controller and cables. Thanks!

EDIT: Just found some strange IDE/sound card. Woo!