Sinclair ZX80 questions

On Aug 22 2006, 17:57, Jules Richardson wrote: back; not. It machine They were all like that, including all the production ones, and the fitting instructions explained how to *remove* the Beeb's own PSU completely, and fit the cable to run it off the Torch disk pack. It was not a good move on Torch's part; I've seen several Beebs completely destroyed as a result of bad PSUs or miswiring. A common problem was that the Z80 card is supposed to fit inside the Beeb, on PCB mounts stuck to the case top with sticky pads. Of course, sometimes those unstick and the Z80 card -- component side down -- falls onto the Beeb's motherboard and shorts things out. If you're lucky, it crashes the Beeb. If you're unlucky, it shorts out the power. This makes the Torch switch-mode detect the over-current and shut down, and in typical SMPSU fashion, immediately try to restart. Unfortunately the regulation in that situation isn't too good and you often get a voltage overshoot. The Beeb's LSTTL does not take kindly to having 9V (approx) pumped into it. I've repaired a couple that had that happen; one of them ended up with every single IC except the NMOS socketed and replaced. It made a nice demo unit for our workshop and an excellent practice setting for our YTS trainee :-) Another one is that Torch used standard 3-core mains cable for the PSU connections, and more than one person, faced with a dismantled system, has connected this "mains cable" to the mains. the Torch spec at systems The maximum current drawn by the Torch Z80 is nominally close to the spare capacity of the Beeb's SMPSU, so they were playing safe in case people had other expansions. Besides, there were still Beebs with linear supplies around when they built the prototypes in early 1982. Yes, there were several PSUs. The original was a black linear power supply, and there were three variants of that (two matt black, one glossy). One "power adaptor/converter" originally used in Model As was so notorious for running hot in upgraded machines or Model Bs that it was nicknamed the "adaptor/exploder", after the failure mode it exhibited. I remember being told in 1982 that "hardly any of these remain in the field". I wonder why. Anyone with a linear supply was offered a free switch-mode upgrade if they fitted a DFS upgrade, or a few other things. The original SMPSU was quite a nice unit made by Astec. This is in a golden coloured metal case, or frame you might say, as it's open on three sides -- which doesn't matter because it's enclosed in the plastic case. Later Acorn had these made under license by BSR, but once again the quality suffered. Most of the BSR units have poorer regulation and less spare capacity than the Astec ones. -- Pete Peter Turnbull Network Manager University of York