ZX Spectrum Marketplace Gamble - Issue 3B Repair and Service 

Thanks John!

C'est la vie! I've been in that situation and it turned out to actually be memory, just took the removal of many chips

Thanks so much Mr It!

All good tips thanks, you're absolutely right

I have a video testing chips on a diagnostic card do you have any dodgy z80, ula or ram multiplexor chips you don't want ?

Hi Lee. I have a pile of them, what do you need? I'm interested in what you're planning to do with knackered chips!

@@HappyLittleDiodes nothing special, I have a diagnostic card with the leds that can show some faults the 0.38 does not show and I made a video recently testing it out with some chips I have and I am about to release a 2nd with some more so just looking for chips I can continue the testing.

@@HappyLittleDiodes If you have any 74ls157 or 74ls32 from the ram multiplexer circuits I have not tested those yet. Or anything that you think could be interesting to test and probe.

I might have some 157's in the graveyard, I'll check later after work

I could have, but the temperatures involved are all within spec and with the heatsink on a stable ULA I decided to keep the original warmth and weight. They are about 6 quid each too and this had already consumed a pricey ULA

Sure, in theory you could externalize the circuit when you have a deaf or mute ULA ... not exactly worth the effort tho since chances are high it will fail more severely sooner or later. Especially when data bits are dead things will get quite complex quickly and signal runtimes might become an issue. Best bets would be either replacements or going with a Harlequin Spectrum. Might be possible to design a "drop in ULA board" based on TTL logic chips which can still be easily obtained BUT that will easily go over the space limit a rubber Spectrum has left.

If you're going this far you might consider looking at one of the clone boards (e.g. Pentagon) that have constructed the ULA using multiple smaller chips

From RS. 3M 9088 Transparent Double Sided Plastic Tape, 9mm x 50m Stock no.:503-4834

@@HappyLittleDiodes Discontinued apparently but that gives me an idea on what to look for ! Cheers :)

A fibreglass pen and I normally use alcoholic spirit and a toothbrush after before a wipe with a cloth

@@HappyLittleDiodes What about using a pencil eraser instead? Fibreglass pens are quite unpleasant to work with and one needs to be careful not to overdo the job. Added bonus: results look way more even.

Thanks Jay!