Sinclair ZX80 / ZX81 / Z88 Forums

That looks great! If you don't mind me asking, where did you get that metal bracket to replace the modulator from? The connector on my modulator is so worn I struggle to get a reliable connection, so something like this would be great but I haven't been able to find anything similar.

I got a similar result from a RAM test and once I replaced one RAM chip all the other errors went away. Check if any of your RAM chips are hotter than the others.

I solved my own issue! I did not realise that the issue 4S has positions for two types of TR4 transistor. I had simply soldered my replacement TR4 into the original holes and this was wrong, so presumably caused TR5 to fry. Having replaced both, and used the second position for TR4 I now have a work...

Hi, I am after some advice on a poorly Issue 4S board that I have. Measuring voltages on the 4116 chips 5V and 0V are fine, but -5 and 12V are missing (very low). When I received the board C78 was already visibly blown so I replaced it. I also suspected that the voltage regulator was faulty so I rep...

I believe that is an official Sinclair modification to the power section that was applied to the issue 3B as well. I don’t think it has anything to do with the speaker - that may have just been removed.

Hi, I'm just reporting back on this thread. The fault was indeed being caused by the 7805 voltage regulator. I replaced it tonight and it is all looking good.

Thanks for the help!

Thanks both - I'll order a replacement in and see if that fixes it ...and hope it didn't take anything else out when it failed!

Thanks Mark Is the heatsink firmly attached? - Yes Are there any signs of anything that could be causing a short circuit on the PCB? - Not that I can see, and this happened after I had been using the Spectrum for about 30 minutes. If you can’t find anything wrong, with the power off, test using the ...

Hi, I am hoping someone can confirm my suspicions on this? I was using my Spectrum+ with an issue 6a board and suddenly it suddenly just died while I was typing up some BASIC :( With no output to the sceen or the speaker I opened it up and checked the voltages on the 4116 chips: pin 1: -4.17 pin 8: ...

So, in an interesting turn of events I was checking the continuity of the circuit board to ensure that the power circuit was all ok and, still suspecting the coil was the culprit, I poked the tip of my multi-meter into the windings to find that one of them was not properly attached - it just lifted ...