Sinclair ZX80 / ZX81 / Z88 Forums

I also think it is a faulty upper-RAM.

Thank you Mark - that's what I meant

@hatman72 I think the answer is in the second sentence of point 5 in Table 1: "Provided there is only one faulty ic at the address". I think there is more than one of the IC's out of order so the PEEK's and POKE's are not very helpful. A other problem I've found on some Speccy's are "perfect" solder...

@gozzo - you can also use 256-RAM's. I'd fixed some Speccys with NEC D41256C, OKI M41256A (always the same refresh cycle) without any problems.

Perfect - you really got an probably faulty Speccy 👍 For the upper RAM fault it is possible that one or more of the IC15-IC22 are damaged. The best solution is to replace all with new RAM's which must all be of the same type. The other way is to swap them one by one and look if the value of the "PRI...

It is also possible, that there is a problem with the contact between expansion bus and smartcard, so the test on an other Speccy doesn't help very much...

IC 29 (a PAL-IC which must be programed) controls memory accesses in conjunction with Z80 and ULA. In the case you didn't swap any RAM's between the tests, there could be a mistake in this area. RAM-test should also be possible without the adapter at the expansion bus. Do you have the same result wi...

I tried it with an Harlequin 128. With 128k-Basic and also 48K Basic it seems to work, but with "PRINT test" I receive "299793". Is this "round-function" the problem?
With "PRINT test - 1.099" I receive "299791.9" so it seems the variable "test" is correctly stored.

looks very mysterious - is it possible to try it with an other monitor or tv? The red lines are looking so perfect - much clearer than the "NEW" prompt

- random pattern - looks like (Upper-)RAM damage