Sinclair ZX80 / ZX81 / Z88 Forums

I'd like to acquire an oscilloscope for ZX81 and Spectrum repairs, also for generally understanding what's going on in them, and for other projects. I used oscilloscopes regularly in a former life, but that was so long ago that I might as well have imagined it. The budget isn't limitless as this was...

Thanks again for your help. I'll leave the capacitor in. It could do with a composite modification, although without a back-porch this could be less than useful - but on the bright side (groan) it does give me something else to think about.

C3 was removed and it tested closed-circuit. The 7805 was also removed and tested with a 1200 supply: 14.3v in, 4.9v out. I had some 22uF, 25V electrolytic capacitors of suitable dimensions and replaced C3 with one of those. No short circuit was present between 9v and ground with C3 removed, nor wit...

https://k1.spdns.de/Vintage/Sinclair/80/Peripherals/RAM%20expansions/Memotech%20Memopak%2016K/PCB/Memopak%2016k%20PCB%20top.jpg Above is a picture of the same version as my Memopak. - 8 x HM4816AP-7 16K x 1 bit DRAMs (single 5v supply, VCC pin 8, pins 1 and 9 NC) - U7805UC 5v regulator Measuring co...

Thanks again for more gems that help me understand what's going on. Forgive the thinking out loud, but having marvelled at the beauty of the aluminium case, I'm now wondering whether that's providing a conduction path - but wouldn't that surely blow the fuse in the PSU? If only I had a bench power s...

Thanks once again for more helpful information. The locating pin is present on the RAM pack edge connector. I'm wary of this, having had a ZX printer lose its pin one day long ago. I'll do some disassembly of the RAM pack and trace the lines from the edge connector around the circuits to see if I ca...

Thanks for the first instalment and the promise of more. It's fascinating. Is it possible that my 1200 PSU isn't up to the job any more and that the voltage under load is dropping below the 12v tolerance of the RAM in the expansion? Would this result in the unchanged snow display? Would it be a good...

I'm new, forgive me for blundering my way at first and thanks for letting me join. I last owned a ZX81 in 1983 and suddenly it's 2021. I now have a ZX81 and a Memotech 16K RAM pack. In 1983 I made do with 1K, in 2021 it's still 1K as something's not quite right. The symptoms: - The ZX81's display wa...

Hello all. I first owned a ZX81 in 1982, it was sold less than a year later to fund a Spectrum. Somehow an Oric-1 came into the mix for a short while before malfunctioning and being replaced by a Spectrum. I never left the Sinclair fold again. I still have my original Spectrum and have kept it going...