DAWE Frecuency Counter
Synthi 100:s, at least most of them, were shipped with DAWE Frequency Counter 3000A. They are not awfully complex devices, but haven’t been able to source any technical documentation on them. Typically they seem to get slightly glitchy, some digits work, some not. Now during my visit to Radio Belgrade III Electronic Studio spend few moments troubleshooting the unit they have, hoping that actual documentation would not be necessary in order to get the unit to function properly.
The device has been set in modular fashion. There is one PCB for each nixie tube, six in total. Then five PCBs for counting logic (?). All PCBs plug together with card edge sockets. Plausible theory regarding the issues with this unit is that the signals don’t travel properly between different parts of the circuit placed in different PCBs. All PCBs were unplugged and contacts were first scrubbed with DeoxIT followed by scrubbing/cleaning with IPA.
The power supply had experienced some questionable maintenance operations in the past. One additional capacitor was placed in parallel of one of the stock ones with long jumper wires and was loose inside the case. That obviously has to go. Ended up recapping the power supply board. One of the caps was totally dead, but it was not the one with parallel add on capacitor which measured just fine.
This Synthi has had grounding issues, and most likely because of that someone thought that lifting the safety ground from the mains power socket would be a smart move. As these issues are now cleared, this potentially lethal ‘mod’ was reverted.
Switches were sprayed DeoxIT. Would be better to really open them and scrub properly. I’m thinking that the main problem was the PSU and the PCB contacts, so thinking that is not necessary for now.
Tested the unit and it is now working as new!