Sinclair ZX80 / ZX81 / Z88 Forums

Thanks a lot Mark ! Glad to see you back ! I should receive soon a 28 pins socket, so I can swap a working spectrum ROM with the "bad" one. But something let me think the ROM is not (the only) the culprit : when my Diag ROM (from Retroleum) runs, it does override the existing ROM (even without ROM o...

I don't have a jailbar effect on this Spectrum but that's interesting, thanks a lot. I had difficulties to find 47nf caps, so now I guess I will order 220nF instead (or 1uF ? Some say it also works fine).

After having checked the Z80, I saw a lot of strange things. I compared this Z80 to a fine working one. Here are the results : On pin 1, I should have 5V but I only have 2V for a few seconds when the Speccy has been turned on, then it goes down to 0V ... On pin 2 and 4, I should have 4.8V but I only...

That's very strange, here are my new investigations : by replacing the RAM chips by others (old and new ram chips are known as working), and mixing different brands of RAM chips, I could find a RAM chips set which is "quite" working fine. I mean that with this set of selected RAM chips, the Spectrum...

I wonder if my problem could come from the RAM capacitors ...

Here is an update of the list of replaced component : - the Z80 - the 74LS04N (IC28) - the ULA - all the lower RAM - all upper RAM - all capacitors - TR4/TR5 - IC27 (replaces IC3 IC4 etc ... on issue 6A). Still no go. My diag ROM still says that there is a RAM addressing problem which may be related...

Strange ! I was just checking the same web page ! But as you said, I have the exact same symptoms but I already replaced all caps, including C44. I will replace it one more time but I'm 99.99% sure it will be useless. But this shows that the problem may come from any electronic component other than ...

Without answers to help, I still try to work on this case. I checked everything I could physically on the motherboard, and saw that the reset button cable was in short circuit ... That's why the CPU had strange readings on its pins. Now the CPU seems to work fine. The display is still the same when ...

I finally replaced TR3, no difference (but I was not expecting much as the clock is present on the Z80). So still investigating ... Here is the current behaviour of the Spectrum : I turn it on, it displays the sinclair copyright. If I don't do nothing with it, then, after about one minute, it resets...

YYYYEEEEESSSS !!!! I finally solved my color problem : I had some doubts about TR1 and TR2, so I checked their voltages, they looked OK (the 0.2v difference I was talking about earlier was not there anymore, I don't know why). I decided anyway to replace them. TR1 is managing luma, I replaced it fir...