I am curious if caps drift in capacitance when in circuit?
I ask because I am working on an old Roberts 770X R2R, circa 1965. After cleaning and lubrication, it's running. However, I noticed a slow down and eventual stop when in Rew mode. When I cancelled the Rew and started it back up, the reels began to move normally for a bit. It's almost like the 2nd engagement 'refreshed' something.
In reading on this topic, it was suggested a motor run cap (1uf, 400VDC, I believe), was suspect.
I also have read about cap reforming-that a cap may reform to work normally by cycling power to it for increasing time periods, to bring it back from sitting unpowered for decades. I will do this cycling, but it did get me thinking about my question. I know that a 20% tolerance cap will vary in actual capacitance from the label, by +/-20% in this case, but how much does a cap fluctuate in capacitance once powered up. If there is obvious change in capacitance during operation-is the cap bad, or is this normal (within the +/- 20%, for instance)
My assumption to this point was a 20% cap might measure, 85% of it's label, for instance, but remain at that value, and not fluctuate.
I ask because I am working on an old Roberts 770X R2R, circa 1965. After cleaning and lubrication, it's running. However, I noticed a slow down and eventual stop when in Rew mode. When I cancelled the Rew and started it back up, the reels began to move normally for a bit. It's almost like the 2nd engagement 'refreshed' something.
In reading on this topic, it was suggested a motor run cap (1uf, 400VDC, I believe), was suspect.
I also have read about cap reforming-that a cap may reform to work normally by cycling power to it for increasing time periods, to bring it back from sitting unpowered for decades. I will do this cycling, but it did get me thinking about my question. I know that a 20% tolerance cap will vary in actual capacitance from the label, by +/-20% in this case, but how much does a cap fluctuate in capacitance once powered up. If there is obvious change in capacitance during operation-is the cap bad, or is this normal (within the +/- 20%, for instance)
My assumption to this point was a 20% cap might measure, 85% of it's label, for instance, but remain at that value, and not fluctuate.