Remanufactured ULAs?

[Rink]

The two ULAs I bought on eBay both work so far, though.... but I want a more constant source. Are you sure your ZX81 has a fully working CPU and RAM?

Hmmm. Mine came from eBay too.

I'm pretty sure about the CPU - scoped the M1 and REFRESH lines etc and they look like healthy signals to me. Not sure about the RAM though... Can't remember if the RAM packs I built disable the internal 1K but that might be a good way of checking if they do. Of course, nothing is socketed on this board.

[Rink]

External RAM introduces seemingly random black marks to the white background. Not really sure what that means... Could just be that the edge connector isn't making good contact, or maybe it points back to the ULA.

[Spirantho]

I've seen that when the ROM is dodgy (you checked that?) and also when there was too much noise on the +5V line (bad disc capacitor!).

Check your RAM and ROM too.

Or just send it to me - I can fix it but I would need to charge £30 for it I'm afraid (it's one of the services I do as part of my business - just handy it doubles up as my hobby )

[Rink]

Cheers mate - this one's not actually my ZX so if I can't figure things out I'll offer your services to my friend. I just end up with broken 81s because people know I've been able to fix a few, but I'm certainly no expert on them.

[Spirantho]

They're actually really simple to fix, but really difficult to diagnose.
First thing to do is to swap any socketed chips.
If you're unlucky, and none of them are socketed, check with a RAM pack as this can help diagnose a bad RAM chip.
Next up is either the ULA (if you have a good soldering iron) or the CPU (if you're a bit more worried about damaging anything). Then the other one of the ULA or CPU, then the RAM, then the ROM.

That, of course, assumes you've already checked you have +5V. That's always the best place to start!

[Spirantho]

I just received my second batch of 10 ULAs - this time from Hong Kong.

Interestingly, these ones look different to the others. They're also cleaner and unused (the others I think were unused but had stains on them).

Even more interestingly, instead of 80% being dead, this time 80% are alive.

These are from
"IC INTERNATIONAL TRADING Co. (Professional IC) "
nancy at ic-international dot hk

They were guaranteed at 20% or less DOA, so they passed the test.

Cost was $12.00ea, shipping cost was $57 by UPS (despatched Monday, arrived today - Wednesday!). Took a week or so for them to get the stock in though.

Edit: Apparently they are able to supply a further 1,000 or so of these chips!

[gozzo]

$57 just to post a few chips!! I'm sure they could do a cheaper option, even if it takes longer to arrive!!

[Spirantho]

It's normal - these dealers aren't usually interested in shipping by mail because they're interested in volume orders - hence they use couriers. The only exception I know of is utsource.net, which have a minimum 1pc order, so it makes sense for them to use regular mail, the resellers like these normally deal in 100's or 1000's of chips, so courier is a standard option. If you buy from bulk stockists from the Far East, you have to expect this kind of thing - but of course if you are buying say a $1000 worth of chips, a courier wouldn't make much difference to the total.

On the plus side, though, 2 day delivery from Hong Kong is a lot better than normal!