Sandy RAM card, PAL blew up.

[Chr$]

This is a Sandy RAM daughter board 512K Issue 2 p/n 10-00738. It fits on top of the Super Q Board (FDD controller etc - 2nd image).

It was installed in a QXT640 (now my QXT640!), originally running happily from the +5v internal power supply. The previous owner unfortunately tested it with a normal QL and put 9v through it.

On the actual Super Q Board main part, I can find no shorts. The RAM daughter board is shorted! The PAL chip top right had blown and has made a bit of a mess (it's just a 2 layer board, right?). I removed it hoping the short would go away, but it didn't. I also removed the RAM chip next to it as it was dark/burned, but that's actually ok and there is still a short on everything.

Before I go any further though, does anyone have the logic for the PAL chip so I can (I assume) replace it with a GAL? Perhaps Dave will see this. Without the PAL it's probably not worth taking it any further and I'll just be happy that the FDD part on its own works.

[XorA]

Blue cap bottom right looks burned, is that your short?

[Chr$]

Blue cap bottom right looks burned, is that your short?

Saw that after posting. Chopped a leg off, short still there. I investigated the 3 blue caps nearest the PAL, they all fell apart on removal, but short still there.

[Maskenlos]

Hi Chris,

to find the short you may consider to apply current 100mA to 200mA with an adjustable power supply. Then just feel which chip gets hot.

Stephan

[Chr$]

Hi Chris,

to find the short you may consider to apply current 100mA to 200mA with an adjustable power supply. Then just feel which chip gets hot.

Stephan

Yeah, but not much point without the PAL info .

[Dave]

Unfortunately, this is a bit out of warranty.

The card is simply a thru-con RAM card with the DIN connectors not fitted. I didn't assemble/test that specific SQB board as mine only had pins fitted where signals were used.

Sorry, I don't have the PAL equations. I wish I did - they would solve a lot of problems. If anyone has them, they're free to release them.

[Chr$]

Thanks Dave.

I note on the back it says 'SUPER THUR-CON RAM CARD 512K'.

Perhaps the brits were simply not used to 'THRU' in those days and thought it should be 'THUR'

It has a date on it too, 2-1-87. A Friday (assuming UK date format).

[Dave]

Hehe, well spotted.

Any other expansion can fit on that connector, so you could use another 512K RAM expansion of a different brand if you like.

Somewhere around here I have a vintage 512Kx8 SRAM version of the thru-con RAM card. It's not too different in logic from the internal 512K expansion. I'm sure you could rustle something up

[Maskenlos]

You may ask whether this guy can read out the PAL content. Probably not 100% exactly the same but it may help to understand.

https://www.nightfallcrew.com/?s=SPEM

Stephan

[Chr$]

Lemme see if I can get this QXT640 working properly first Dave. It came with loose bits flying about in the case. First patient is the Astec PSU, it had an exploded filter cap and functionality is unknown until I get that (and 2 more suspect looking ones) replaced.

I'll probably post a QXT640 thread at some point with pics and no doubt some questions along the way.

Thanks Stephan. I think that would likely take up a lot of time/work/experimentation. I can just put an internal new 512k RAM board into it if it comes down to it, although I would like to keep it original hence trying to repair the PSU instead of just getting a new one.