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.
