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How do the notorious black flag capacitors fail?

Outstanding write up! Thank you for explaining this so clearly, that a dolt like me can understand.
Thanks to all that have contributed to the info on this great forum.
 
Guess I'm a results junkie...I wanna figure out what went wrong, fix it, and get it the hell out of there (since I've probably been messing with it for a week already as it is). I am curious as to the specific failure modes, and from time to time this is made clear by the chain of devices in the failure. But mostly, it's just a case of 'the damn thing just blew up' and rather than spend time figuring out why (which, as I'm sure you know, is its own engineering discipline, and one in which I share only a modicum of interest) I'd rather just move on to the next disaster.

Thanks for not making me feel like any more of a clod than I already do.
 
A clod with 25k+ very useful posts? Ha, I rather doubt it. I do think the detail oriented mindset that allows one to fix stuff also lends itself to somewhat harsh self evaluations. Yesterday I spent more than an hour looking for what seemed an elusive problem with a Fender, taking apart way more than I had to. Turned out to be a simple dead filter cap. Newer unit so I never suspected the PS or bothered to test it- the symptoms pointed elsewhere. Ten minute fix; stupid me. Today I spent the entire day just working up enough ambition to actually power up the scope and fix stuff. And so it goes, joy when things work, frustration when they don't. (need tragedy/comedy emoticon here!)
 
ConradH said:
It will probably change a bit, depending on what feedback I get, but here's a page on the black flag caps.
Click to expand...

I really appreciate this (being the kind of guy that likes things being visualized and measured to get a better understanding of how things work or - perhaps better in this context - do not work).

So, great piece of work with of course the well deserved credits to Glenn.
 
I am rebuilding a Kenwood KA-701 at the moment. There are quite a few square "Black Flag" caps in this amplifier. Thanks for identifying this EchoWars. I plan on using silver mica to replace them, unless anyone else has any better ideas. There are quite a few. First time I've ran across them.
 
You can use Ceramic COG/NP0 replacements and usually they are much cheaper. There isn't much between the two possible replacements (Silver Mica and Ceramic), however, the ceramics are reckoned to be better overall. I have used both with no discernible difference when comparing two same model amplifiers, one with Silver Mica and one with Ceramic.
 
I personally reckon it's the potting/epoxy/compound that reacts with the internals over time and causes 'black flags'* to go open or low.

We have so many elements in electronic components, sitting sealed in environments where gassing off of petrochemical based substances and heavy metals can react and cause some crazy chit to happen.

We have brown-goo (Sansui et al) and all the problems it causes, all those chemical reactions.
We have capacitor electrolyte and lead/tin/copper and we all know that is a lot of fun (not) in the long term.
Silver plating over copper, epoxy and black lead migration issues on transistors
Tin whiskers on old Ge devices.
We've got Cadmium plating (and tin?) making the weirdest spider webs inside old speakers.

My favourite one now, is salt air (I am near the coast) attacking tin plated copper leads and migrating into the actual junctions of glass encased zeners and playing havoc with regulator sections.

* Attributed to Glenn (I'd always thought it was like the fly killer except they looked like little flags- personally I thought it was a great nickname for the little bastards)
 
Hey guys, can someone post some pics of the "black flag caps", for the life of me I can not determine if I have ever seen one. Are they particular to Sansui? I have seen plenty of the small value flat, green caps.
 
Excellent! Don't recollect seeing those before but been a long time since I worked on a Sansui.
Just getting interested in audio again after retirement from defense ind.
 
EchoWars said:
Pointed out the issue with these caps here in the forums with the Kenny L-07MII in January of 2007, and with the 919 later in October of the same year. And yes, I coined the label 'Black Flag' since that's what they looked like and that they 'killed amps DEAD!' (RAID commercial the old-timers might remember):D

I totally understand that you are trying to help people (and that's why I hang out here...for the love of old gear), but when I do a write-up, I try to credit those who blazed the trail for specific solutions and fixes. I wish you'd do the same.

Edit: Try as I might, I could not seem to find a way to say what I wanted to say without sounding petty. But I've spent thousands of bench hours finding answers to both common and uncommon problems with vintage gear, and I'm proud of what I've been able to accomplish. I have a pretty good string of fixes and firsts when it comes to repairing 70's Japanese gear where NOS parts are long gone. Background - Most of my career before this in repairing and troubleshooting robotics was spent finding solutions that the engineers either overlooked, or were too close to the issue to see the system as a whole. In nearly every case, guess who got credit for the fix and sometimes even a patent on my ideas? Hint: not me.

So maybe I'm a little sensitive here. If that's the case, forgive me. Just seemed to strike me sideways to see a page that was put together as a "Hey, look what I found!" when I pointed this stuff out to AK members years ago. I do like the detailed write-up (which I never bothered to do), as well as the servicing notes.

Anyway, if I'm out of line here, I'll gladly delete this post.
Click to expand...

Well it's been this long and I don't see any likes.

So black flag caps™, must learn what to replace them with. I shall read on. I suspect poly radials, but this is just a guess.
 
McGowdog said:
I suspect poly radials, but this is just a guess.
Click to expand...
You could, if you can find 'poly radials' in the values commonly used, so far I have found:- 1pF,2,3,4,5,6,9, 10pF, 22pF, 30pF, 33pF, 47pF, 91pF note that they must be 'radial' construction, not axial as the additional lead inductance would be detrimental. After trying Mica and Ceramic, I have settled on Ceramic as my standard replacement as they are physically really tiny (less stray capacitance), are easily available in the values required, are cheaper, and perform well providing they are C0G/NP0 type.
 
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