I did say in post two that I have another one of these signal generators and it has come to the head of the do do pile while the internal layout and diagrams are to hand.
This one has a report that the meter is open circuit.
A meter of the same outline with a scale showing 100ua FSD was with this instrument.
For some strange reason there was an EC90 taped in to the space between the smoothing choke and the chassis. This is not related in any way to any of the valves in the instrument?
Also some notes have been scribbled onto the chassis.
Before replacing the meter the fault that damaged it must be found so the cap reforming started with an allowance for a potential divider across the HT.
R24 (first photo in post #1) started to get hot during the second phase of cap reforming.
This was very intermittent.
Previously an engineer or twiddler had been probing the center tap on the audio oscillator coil L7 to such an extent that the wire that leads into the core had become damaged. I had to dig all the varnish out of the tag on the coil in order to get a good connection again.
This work revealed another intermittent short circuit between the center tap of the coil and ground.
C19 was getting hot and making a noise so that was next and also one end of C74 came off its tag so I tested it and found it reading 3 meg so I replaced both of them.
The intermittent short in C19 would account for pulses getting into the meter causing it to fail.
Some how the diodes had survived and did not need to be replaced.
With a DMM attached I powered up with the Variac and all was fine so success was just a matter of replacing the meter. I had to open out the solder tags due to the terminals on the new meter being larger.
The meter Is reading slightly high so a check of C20 and C105 will have to be done before the covers go back on.
This one has a report that the meter is open circuit.
A meter of the same outline with a scale showing 100ua FSD was with this instrument.
For some strange reason there was an EC90 taped in to the space between the smoothing choke and the chassis. This is not related in any way to any of the valves in the instrument?
Also some notes have been scribbled onto the chassis.
Before replacing the meter the fault that damaged it must be found so the cap reforming started with an allowance for a potential divider across the HT.
R24 (first photo in post #1) started to get hot during the second phase of cap reforming.
This was very intermittent.
Previously an engineer or twiddler had been probing the center tap on the audio oscillator coil L7 to such an extent that the wire that leads into the core had become damaged. I had to dig all the varnish out of the tag on the coil in order to get a good connection again.
This work revealed another intermittent short circuit between the center tap of the coil and ground.
C19 was getting hot and making a noise so that was next and also one end of C74 came off its tag so I tested it and found it reading 3 meg so I replaced both of them.
The intermittent short in C19 would account for pulses getting into the meter causing it to fail.
Some how the diodes had survived and did not need to be replaced.
With a DMM attached I powered up with the Variac and all was fine so success was just a matter of replacing the meter. I had to open out the solder tags due to the terminals on the new meter being larger.
The meter Is reading slightly high so a check of C20 and C105 will have to be done before the covers go back on.
