Self-healing Sony EV-S7000 capacitors?
 

An observation FWIW.

A Sony EV-S7000 Hi8 VCR that had sat idle for a number of years (over 5) was exhibiting significant color noise on tapes. The image, though stable, bordered on unwatchable and was useless as a capture source. Did capture using a GV-D200, and used the EV-S7000 for tape rewind and logging due to its far superior tape handling characteristics, so it was powered on.

After probably 10-20 hours power up noticed a significant portion of the noise had cleared up. While is is not yet back to its original state or a match for the GV-D200 analog output, it is much better than it was and OK for watching non critical material.

Attribute this to electrolytic capacitor self-healing over time when powered. It is not an assured thing, but worth trying if there is no evidence of catastrophic capacitor failure (e.g., leaks). It is probably not going to help issues such as the classic AG-1980 SMD capacitor failures.

Is this a known property of capacitors, or your pet theory? Sorry, I know next to nothing about electronic components at this level.

Of some types of capacitors, not all. Well known in the older ham radio operator circles, but not well known in others. My theory is that it applies to at least some of the caps in the EV-S7000.

https://en.wikipedia.org/wiki/Electr...lication_rules

Yes, your conclusion is likely correct, however they are likely needing replacement in the not so distant future as they are unlikely to be working to spec - just working well enough as it were.

The classic fix talked about for caps is usually referring the large electrolytic power supply filters in antique radios. Remember though what matters is the actual DC volts being applied to the caps in question so switching power supplies and other modern design electronics may require a workaround. A switching power supply may not even turn on till the volts hits 80%.
The method is to bring up power in stages over a period of several hours. You watch total current so as not to over power the degraded caps while they are "reforming"

to bring power up slowly a variac (variable autotransformer) or is needed the good ones have current meter and volt meter included to keep track of the punishment you are applying to the old caps.

Attachment 7461

I use one of these Sencore isolation power supplys.
Those old caps were filtering a few hundred volts to supply vacuum tubes so the newer low voltage caps may be self healing with 5 or 15 volts no increments of supplied voltage required. If you are powering up and ancient radio or tv it is a good idea to use the variac and move slowly

Old electrolytic capacitors that are near failure will sometimes "work" after being heated up. That is, any noise or buzzing audio in the signal path was subside. Given that its an early 90s piece of Sony equipment, all the surface mount capacitors should be replaced and the board cleaned as the electrolyte that leaks out of them is corrosive.

My experience has always been caps get worse when heated. This is the second issue I've read about in the past week where leaving something on is showing improvement. That's odd to me. Never heard of or seen that.

@NJRoadfan, is capacitor explosion a possible issue here? :hmm:

Standard wet electrolytic aluminum capacitors don't tend to explode. Tantalum capacitors do go out with a bang when they fail shorted. The concern with older tube equipment has to do with ancient capacitors that saw MUCH higher voltages then modern transistor equipment. If a cap failed with a short, things could burn out in short order and some stuff could pop.

The biggest concern with modern electronics is getting the corrosive electrolyte that leaked out of the old caps off of the board, as it can eat traces away and corrode parts of the board to the point that it can't be repaired.