How do the notorious black flag capacitors fail?
- Thread starter ConradH
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Conrad; By "black flag" are you talking about the Suzuki PIO's, or a film cap. The Suzuki's look like they short from drying out(or leaking out) and then "explode" leaving paper and parts all over. Not good for those with Cardiac problems. About 1/2 of them in my 1000A let loose when I brought it up on a variac the 1st time (before I rebuilt it).
The plastic encased axial caps can expand, and split the case. Usually from the same problem as the Suzuki's.
Larry
The plastic encased axial caps can expand, and split the case. Usually from the same problem as the Suzuki's.
Larry
ConradH
Lunatic Member
I don't know exactly what they are, but probably silver-mica or a low loss ceramic. They're small flat rectangles, black, and look like... a small black flag on two legs! Typical values are 3, 6, 9, 22 & 33 pF. When my replacements come in and I pull them all out of a 919, I'll do some measurements and try to figure out exactly what they are. IMO, even a new silver-mica replacement has some small chance of failure compared to an NP0, but the silver micas are usually more available, at least for a price. Since they have such a bad reputation, I'm just curious how they fail.
I'd always supposed that they were an early sort of stacked ceramic. Most measure OK at low voltages, but fluctuate under load. Both Kenwood and Sansui seemed to be fond of them for a few years.
Post #4 here: http://www.audiokarma.org/forums/showthread.php?t=345020
Post #4 here: http://www.audiokarma.org/forums/showthread.php?t=345020
That is also my understanding.
ConradH
Lunatic Member
That's true, but at the single pF level it's going to be a single layer ceramic of excellent properties unless it were some tiny SMT thing.
The losses of the black flags I measured were near zero, so I suppose styrene is possible. When I change 'em I'll bust one in half to investigate further. No, it doesn't matter, I just want to know!
The losses of the black flags I measured were near zero, so I suppose styrene is possible. When I change 'em I'll bust one in half to investigate further. No, it doesn't matter, I just want to know!
Black Flag Capacitors
I do have an AU 919 schematic with a parts list and a list of abbreviations. The capacitor abbreviations are BP.E.C. for bipolar electrolytic, C.C. for ceramic, E.C. for electrolytic, M.C. for mylar, Mi.C. for mica, O.C. for oil, P.C. for polystyrene, and T.C. for tantalum. Looking at the schematic the P.C. (polystyrene capacitors) come in 3, 5, 9, 22, 33, 100, 390, 1000, 2000, 3000 pF flavors of those rated at 125V and this list must include the black flags. The P.C. capacitors also come in other flavors but at 250V such as 0.1 microF. So, FWIW, I think that all of the black flag capacitors are polystyrene. Why some polystyrenes at the 125V rating tend to fail and others such as the 1000 pF 125V P.C. or the 250V P.C. capacitors which are presumably not black flags do not I can't say.
Marc
I do have an AU 919 schematic with a parts list and a list of abbreviations. The capacitor abbreviations are BP.E.C. for bipolar electrolytic, C.C. for ceramic, E.C. for electrolytic, M.C. for mylar, Mi.C. for mica, O.C. for oil, P.C. for polystyrene, and T.C. for tantalum. Looking at the schematic the P.C. (polystyrene capacitors) come in 3, 5, 9, 22, 33, 100, 390, 1000, 2000, 3000 pF flavors of those rated at 125V and this list must include the black flags. The P.C. capacitors also come in other flavors but at 250V such as 0.1 microF. So, FWIW, I think that all of the black flag capacitors are polystyrene. Why some polystyrenes at the 125V rating tend to fail and others such as the 1000 pF 125V P.C. or the 250V P.C. capacitors which are presumably not black flags do not I can't say.
Marc
ConradH
Lunatic Member
OK, some new data. I haven't busted one open yet to see what it is, but I measured the pulls from a Sansui amp I'm doing some work on. No problem with the 33 pF. No problem with the 22 pF. The 3 pF however, had a 50% failure rate. Yes, half were bad! The exact failure was low capacitance, as much as -77%. The low value parts also had higher dissipation factors and gave unstable and noisy results on the bridge.
I don't know about the other values, but the 3 pF version most certainly has a huge problem and I can see where it could be an amp killer if it goes into oscillation, something likely with the original high speed outputs. With replacement outputs I saw a rise in response at a few hundred kHz, very undesirable, but no actual oscillation. I'll check more when I get to the parts on the other board.
I don't know about the other values, but the 3 pF version most certainly has a huge problem and I can see where it could be an amp killer if it goes into oscillation, something likely with the original high speed outputs. With replacement outputs I saw a rise in response at a few hundred kHz, very undesirable, but no actual oscillation. I'll check more when I get to the parts on the other board.
ConradH
Lunatic Member
Doing a decent measurement on a 3 pF cap is subject to a lot of errors. Ideally one would put it in a special divided box and make a fully shielded measurement. Not being quite that crazy, I did a 3-terminal measurement using clips off a banana plug. The open circuit capacitance of the bridge and plug was 1.311 pF with a dissipation factor of 0.0033 at 1 kHz (series). Apparently plastic dual banana plugs are a bit lossy compared to air. A typical good black flag was 4.41-1.311 pF with a D of 0.002, so you have 3.01 pF and a dissipation near enough to zero, since it's so close to the bridge residual.
A bad black flag was 1.98-1.311 with a D of 0.02, or 0.669 pF with high losses and a lot of instability/noise. IMO, that would be an amp killer!
The residual readings don't get so much involved with the larger values, and the dissipation factor of the 33 pF parts was about 0.0006, which suggests either a good ceramic or a good film like polystyrene. I'll get my hammer out later.
Without a good bridge these can be tough to measure, but an old school technique that would work great would be to parallel the caps with a coil and find the resonance with a grid dip meter or other means.
A bad black flag was 1.98-1.311 with a D of 0.02, or 0.669 pF with high losses and a lot of instability/noise. IMO, that would be an amp killer!
The residual readings don't get so much involved with the larger values, and the dissipation factor of the 33 pF parts was about 0.0006, which suggests either a good ceramic or a good film like polystyrene. I'll get my hammer out later.
Without a good bridge these can be tough to measure, but an old school technique that would work great would be to parallel the caps with a coil and find the resonance with a grid dip meter or other means.
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)
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.
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.
It didn't come across like that to me Glenn, but that's perhaps because I know who did the foundations of this work. :yes: (I have personally been repeating your words on the subject many times).
It just draws together of as much of the information about black flags as possible. However nobody has cut one open until now, or proved that they are polystyrene, or forensically plotted their values as removed - shown as new information here.
I was particularly delighted by the appropriately dire warning on their continued use.
It just draws together of as much of the information about black flags as possible. However nobody has cut one open until now, or proved that they are polystyrene, or forensically plotted their values as removed - shown as new information here.
I was particularly delighted by the appropriately dire warning on their continued use.
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ConradH
Lunatic Member
EchoWars, not petty at all. As you probably know, I'm a measurement junkie, and understanding the failure mechanisms is my "thing". I certainly lay no claim to discovering anything regarding this, just trying to get the tech info compiled in one place, with some supporting measurement data that most people probably aren't equipped to collect. I'll add some history & credits- gimme 5 minutes and we'll edit as needed. You may need to refresh your browser lest it pull the old page from the cache.