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Excellent work! Glad that you have made good progress :D As it seems common for MTX's to be marked / cased as MTX512 , but to have 32k DRAM chips, I wonder if they were suppose to be sold with the 32k memory board. But if so, where are all these memory boards? I suppose some of the MTX512's with MTX...

Actually old DRAM is fairly power hungry :( Still thinking about this. The problem is:- (1) the 16k DRAM chips used for the video RAM needs +12V, +5V and -5V and all three need to power up at the same time (or in the correct order), (2) the rectifier system is a number of half-wave types back to bac...

Okay, found time to do some measurements on one of my MTX's. The MTX is a "standard" MTX500 with no modifications or extras. These results are all from a faulty machine (I just get a continuous tone on the sound and no display) as it does not have a keyboard attached, but the power supply ...

Hmm, I have a MTX512 S2 that came with a SDX drive fixed to it. The machine has a combined serial RS232 & 80 col. board inside. Not that I have got the computer and drive to work yet... Are we saying the there was a mistake in the original PAL programming on the original serial boards? Edit: aft...

I guess the other thing I could do for the -5v would be to replace the Zenner / R60 with a 7905 -5V reg + caps. You could, but I expect the current used on this supply to be low. A 1A rated voltage regulator may be a bit overkill! I think the existing resister should be okay, but until I have teste...

Hi Mark, given a choice, would you do the DC mods, or try to build the replacement AC PSU that you descibed in the ZX forum? regards Dave Well, I have two original Memotech PSU's (transformers), but four Memotech computers, two of which work, and two of which have faults. I think I only have one sp...

Hi Phill, and welcome! :D For the +5V line I suggest you also remove Q4 or FS1. For the -12V feed, to supply the correct voltage and current for the -5V line, you may need to change the value of R60 (the 1K resistor). Myself, if I was going to convert a Memotech to use an external dc PSU, I would do...

Hello there! Well first, the way I found my way here was via Dave contacting me at StarDot forums (the forum for Acorn Atom, BBC Micro, Electron and Archimedes machines and users) asking a Memotech related question. I then investigated a link in a follow up PM to me. The link took me to Andys Memote...