Hi all.

Recently I have begun to hear discussions of,
Changes of Fault Patterns.

Basically, this refers to the Stock Faults, which we have become familiar with with each new piece of electronic equipment, and what we are now experiencing as the products now are exhibiting new fault patterns due to their extreme age, and or storage environment.

Components have now had decades of time for all the little chemical time bombs to succumb. Electrolytic caps either drying out or having their legs corrode away. Moisture working its way into transformers, corrosion working its way along the leads of glass diodes and into the junction.

I've seen an “ADSL Central Line Filter,” mounted in a damp area of a room, have the circuit board become conductive knocking out services.

Currently, I am working, (whenever time permits), on a couple of colour TV's for a member of this forum. With these two sets, the familiar stock faults are all there, but I am experiencing a host of new faults as well.

Has anyone ever seen the cap that goes across the Horizontal transistor sizzle like a steak on a BBQ? Popping the end cap?
The light green ones used to just go open, causing the E.H.T. to go so high that it would punch a hole through the neck of the tube, under the yolk. Although I have a number of new old stock caps for this position, I am scared to fit one. Doing research. The service manual tells me that the original caps were Paper Polypropylene. I have some candidates to replace the original type. I have to consult a certain member as to what he uses as a safe replacement.

Updates to follow as soon as possible.

Funny you should mention that Labrat.
Recently I have found numerous leaky/noisy(silver migration) Mica capacitors in my vintage repairs.
I have been in the industry my entire working life, and say 30 years ago I may have come across a few faulty mica's in hundreds of repairs.
Recently in the last dozen or so repairs/restorations many mica's have been faulty.
Also numerous 100pF mica's noisy found in valve stereo systems.
Never before have I seen so many faulty. Obviously moisture age and voltage have caused problems.
All mica's recently found faulty were in situations where approx 100 volts DC was on them.
As a matter of interest Labrat, I also have a stock of those green high voltage caps, but not used for many many years.
JJ

American Silver Mica caps always have had issues with Silver migration, or it growing whiskers & shorting. Of course like plastic bags they greenified solder. Now we get a brittle solder & "Tin Whiskers". It was well known before they started WWII that Tin, Silver and a few others put out whiskers. It took a certain percentage of lead to stop that.

We suddenly have a timber shortage. Of course the brainwashed, where only a light rinse is required to accomplish that; would not be able to compute that 20% of paper bags is new cellulose and trees are a convenient way of getting it.

Do note the this is the age of greed & consumerism: Chuck it don't fix it. Money & Climate change are the new Messiah.

Marc

Labrat I'm sure you're talking about Philips K9 chassis sets. Originally they had 2 caps in parallel across the Hor O/P transistor to make up 11nf. (I think).

If one went open circuit the EHT went up to silly numbers and punched through the glass to the yoke. I saw this several times in a previous life as a service tech.

The fix was to have a single 11nf higher spec'd cap. If it went open circuit the BU109 O/P transistor would fail, going short circuit collector to emitter and no other damage done.

Talking about failure of very old components I've heard of people now finding Philips Mustard caps leaky. I have never found one crook in all my years of fixing gear but it looks like their time has come also.

An interesting thread, and very fitting in these times where we are living longer on average and experiencing chronic conditions unheard of in our predecessors. Very fitting. Nature does have an incredible sense of humour.

I would have considered a mica cap a very low suspect component in my servicing years, and as for Philips mustard caps, I also never had to replace one.

Good thought provoking thread.

There are a few brands & types of capacitor that were rare here, but American sets did get here and brought their issues with them. There Silver Mica caps gave trouble & must have been made differently. We have a Mica cap here AWA made some & they were crimped, some times waxed, or hard jacketed. They from the mid 30's were virtually indestructable.

On the other side of the coin I had a run of Midwest's and have had others with components marked "Micamold" . That is a brand and most of them are not Mica and I have gotten to the point where anything branded that is bin fodder: Nightmare.

I have some of the correct caps. I've seen the sizzling you refer to when the wrong cap is used.

Drop me an email.