Sinclair ZX80 / ZX81 / Z88 Forums

Fantastic answer, thanks a lot, this exactly what I needed !
I will do all these tests tomorrow and let you know.

Sorry Mark, finally I could find out the answer about the jumpers "N" or "H". But I still have this question for you regarding my no sound problem : I replaced TR7, same issue : no sound. I tried to connect the existing speaker to one on a working Spectrum : still no sound. I know that D9 could be t...

The only source for ROM chips, is from people who repair ZX Spectrums or who cannibalise boards / computers. If Phil at Retroleum does not have one, try Ben at bytedelight or Ian at mutant-caterpillar . Or on trading sites like eBay... Mark Mark, I could find some ROMs on the Retroleum website, but...

Thanks a lot Mark ! But now I remembered I have another problem on this Spectrum to solve : no sound ... I replaced TR7, same issue : no sound. I tried to connect the existing speaker to one on a working Spectrum : still no sound. I know that D9 could be the culprit, but I need to find one to buy, i...

YYYYYYYYYEEEEEEEEEEESSSSSSSSSSSS !!!!!!!! Thanks a million again Mark !!!!! That was it ! I removed the ROM from the motherboard, and now all the diag ROM pass ! So now, I need to find a second hand ROM, or to use an EPROM instead. Retroleum sells some programmed EPROM for a very decent price. If I ...

Yes, what I call the "Diag ROM" is the Smartcard from Retroleum.
Do you mean that a failing ROM on the motherboard could cause the diagnotic ROM to fail its RAM tests ?
If yes, maybe I should just remove the ROM from the motherboard and see how the diagnotic ROM behaves.

No problem Mark (thanks again a million to you for trying to help me !). Symptom : after one minute of use, the Spectrum displays some bugs on the very left side of the screen (colors or characters), sometimes resets itself, and a lot of games do not load. The Smartcard Diag ROM sometimes say one or...

I confirm : I took the whole RAM set from my none working Spectrum (the RAM set which fails when doing the code execution with my Diag ROM), and on the working Spectrum the code execution RAM test works fine. So there is definitly a component on my motherboard which let the RAM not working fine. Wil...

Mark, as said earlier, the problem is that with any set of RAM chips (I tried 3 different sets of working RAM, each set with same brand and same model of RAMs), but it always ends up with one or more RAM chip said as "bad" by my Diag ROM. So I am 100% sure that my problem does not come from the RAM,...

Mark, thanks for your answer, I will try to re-launh the code execution test with some other RAM, trying to get all of them at the same speed, 150ns minimum. Will let you know about my result.