Intermittent Static Noise from 5210

[Lobsterjo]

I have a 5210 that has a snap-crackle intermittent static noise which seems to disappear after the amp is on for 10-15 minutes, longer if it's been sitting for weeks. Seems to be in the output stage as whether or not input, FS or FX loop are connected or front panel settings has no effect . Have already changed the power supply filter caps. and it was working fine until I fired it up after a months long "sit". Tap tested the PC board too. Nothing appears loose. Any suggestions to narrow this down: a transistor, IC, resistor or one of the smaller electrolytics? I can do soldering but not good at tracing signal through a circuit with a scope...Thanks in advance

 

[Tatzmann]

First try to narrow it down.

Monitor the effects send to
determine if its infront or behind it.

 

[Lobsterjo]

Traded this amp with a good acquaintance for a guitar today but would still like to remedy the issue.
@Tatzmann: the noise does not come through the effects send.

 

[Pete Farrington]

one of the smaller electrolytics?

Ecaps aren’t like other components, they’re electrochemical like batteries, they wear out when in use and degrade when they’re left unpolarised for a long time.

With old stuff just assume they’re at least walking wounded, possibly dead, and replace them all.

 

[blademaster2]

I had a friend who said that his 5210 had been in repair shops several times with a similar crackle/pop that could be heard intermittently. No one could find what was causing it.

He gave it to me and I had a look at it, made some measurements, and discovered that there was a tantalum capacitor used for coupling in the signal path that was slightly reverse biased. It was assembled correctly, so I concluded that the circuit design was perhaps flawed from the start (or the dc voltages drifted over time, still not a good design if that was the reason here). I replaced it with a bipolar electrolytic capacitor of similar value (the value is not terribly important to match precisely in this application).

That did the trick. I paid him a small amount for the amp to cover his costs for the new speaker he had installed and I have used it for more than 15 years since then with no trouble.

I forget which capacitor it was offhand, but if anyone thinks their 5210 has the same trouble please ask me and I can dig up my notes on it.