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I used to supervise a service team of 14 guys and other things. Carlson would not have been one.? Servicing is about probability, experience and logical inference but it all needs to be based on sound theory, you also need to take less than a month to fix things, glacial is not an acceptable speed setting. Droning? on and on about outer foil? again and again and again shows a lack of focus on what matters at AF & LF in the crap he deals with. But it must impress someone.

Capacitors are usualy very reliable but 60 year old paper dielectrics are often way beyond their use by date, there's not much point in NOT replacing such parts unless you have a stationary exhibit in a museum. Any old electrolytic also qualifies for retirement. Why would you leave a part known to fail in place only to have to change it some time soon? For a lot of Tube gear the big issue is with AF coupling caps, there are not that many, replacing old paper caps with modern plastic film types is a no-brainer providing that you can get decent replacements. If you speak to people used to servicing particular gear they may let you know particular liable to fail parts. Stock faults are common to all kinds of electronics, there used to be particular brands which were more liable to cause problems. Long time back there were some electrolytics in plastic cases that were very unreliable. One of the causes of electrolytics failing was sweat, one trace on a foil or paper would condem the part eventually. Bead tantalum capacitors are another "Replace on Sight" part, they fail to a very short circuit. On the other hand mil spec tantalums in cans are very reliable, the flat disk "acid" types are possably the best electrolytics ever made, now at ransome price levels.

An ESR meter needs to deal with series resistances? under 0.2 ohms for larger caps ( e.g. 220-4700 uF). The failure is mainly due to ripple current at high operating temps or running cheap electrolytics where higher rated parts are needed. So a useful ESR meter needs to read down to 0.1 ohms or lower.? It also needs to be fast settling in a pro setting, waiting more than a second or two is as useful as toothache when you want to check every at risk part. I used an Electronic Design Specialists EDS 88A when I was doing it for real, that was a very effective tool. ESR meters are absolutely vital when working on switch mode supplies. Now for a True Story about ESR.

There was one product that failed after 6-18 months, we had about 800 in the field. It was a CRT monitor. It would fail with extensive damage to the Flyback Transformer and shorted Horizontal Output transistor.? If you replaced all of the failed parts it would work again then 1-30 days later you needed to replace all of the parts again. The ESR meter found a small 22uF cap in the switching supply that had high ESR. When I checked the part it turned out that the manufacturer had changed the part, the new part had a smaller can.? Smaller can = lower ripple current rating. After a while the capacitor ESR went higher when the product was warm causing the rail to the Horizontal output to increase and do extensive damage. Turns out that some "Value Study" had saved a few cents on one cap without checking the consequences. That cost the Company it's reputation that had developed in 50 years of manufacturing.

I still use the EDS88A, but also have a? Vanwell Chinese multi-function tester, it's surprisingly good for many semiconductors and will indicate ESR for electrolytics down to 0.1 0hms. It's? too slow for pro use but much better than toothache, good for hobby users and very inexpensive.But a lot of dirt cheap Chinese RCL meters that I have seen are very inaccurate. For RCL indications for rough work? I use a Peak LCR45, that has a good wide autorange for AF and RF use and is accurate.

Regards,

Alan G8LCO