Thank you Martin for the detailed report! I wonder how many of those machines are still around, just in case a fully working calculator can be put together from parts. But probably the display is the toughest component in there!
Maybe the damage was caused by a lightning strike, at least I experienced similar faults when I tried repairs after those events. Hard! Congratulations for fixing the PSU. Paolo Il Mar 22 Ott 2019, 01:38 Dekatron42 <[email protected]> ha scritto: > Well, the ZM1200 Pandicon is working as it should on all digits, but the > calculator itself isn't, it is almost completely dead. There are only four > signals from the main board to the Pandicon board that shows any life > whatsoever, a pity now that the power supply works. > > The power supply is not such a good design because when you switch it off > the oscillator for the transformer goes into self oscillation and the UJT > controlling the SCR also drives the SCR into full conduction which means > that at the moment of switching off the output voltages rises a lot! There > is no regulation feedback on the output voltages and maybe this poor design > is the reason for the calculator not working, just guessing here but the > voltages were several 10's of volts higher than written on the circuit > board just at switch off and you can see flashes inside the Pandicon. Maybe > a fully working calculator doesn't see this over-voltage spikes but I think > it will even if it draws more power working. > > There were a lot more bad soldering, dry joints and corrosion on the main > board, it smells like a rat has peed on it and it looks like that in some > places. I cleaned all of the corroded areas and checked all of the traces > and components. Now, the 10% resistors are at least 10% high so those might > affect the overall workings, might change some to see if that differs. I > changed two small electrolytic capacitors looking like Tantalum bead > capacitors but that didn't change anything. Transistors and diodes are ok, > but I had to re-solder a few of them as I could easily see the dry joints > and also measure the dry joint as I only got contact when touching the pin > of the transistor and not the trace it was soldered to, as is the keyboard > magnetic switches but the ic's all are non responsive, not a single pulse > anywhere except for the four signals to the Pandicon board. > > Well, it was the Pandicon I was after knowing that the seller had > disconnected the power supply due to problems previously, but it would have > been nice if the calculator had worked. > > So, if anyone has any ideas on what to check to get it running I would be > happy if you could write a line here or send me a message offline. > > I hope someone can have use for the circuit diagram of the power supply. > > /Martin > > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/6ef531e8-0ee0-4eaf-8833-011bb16a3078%40googlegroups.com > <https://groups.google.com/d/msgid/neonixie-l/6ef531e8-0ee0-4eaf-8833-011bb16a3078%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/CABj2VaYQeOs0UqBaWqSBDJEvQiDR7i3Kia9C6g1wmT5ws653bg%40mail.gmail.com.
