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what causes a Sansui Ca-F1 preamplifier to blow my power amplifiers?

If they are repairing the amps then have them connect that pre-amp to them right at the shop and prove it out with their freshly done repairs. I know they will not want to rebuild the amp again so they will "tread lightly" and it may also rule out some crazy power or ground looping issue by using their power and bench.

Its certainly a weird issue...
 
he repair on the onkyo was done last year and that's how long my preamp has been benched at home. I should have thought about taking my preamp back and have him connect it to the amp when I picked it up like you said. As for the sansui b-2101 he said transformer was shot.
 
lopezluna said:
he repair on the onkyo was done last year and that's how long my preamp has been benched at home. I should have thought about taking my preamp back and have him connect it to the amp when I picked it up like you said. As for the sansui b-2101 he said transformer was shot.
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That really is extraordinary! I can't imagine a pre-amp fault that would take out a power transformer - especially in a Sansui amp. :no: - not that I doubt Fred Longworth - but wow - that is amazing. (UNLESS... the fuses had seriously wrong ratings...)
 
I don't want to say anything bad about that shop, but I got the sansui amp repaired bi someone else. Transformer ended up being good. A coworker that lives in Mexico took it to a guy and had the amp repaired. I no longer have ties to that coworker though. At the time I was limited to cash too so I didn't give him the preamp to have repaired too.
 
There are a small handful of the black mica caps in that there preamp. I have also yet to see one of these preamps that did not need a full recap.

My money is on the mica caps drifted out of range and is causing funny things at the output. It may be intermittent or may not show up without being loaded!!

These caps being in range are absolutely detrimental to the stability of this preamp. It needs someone in there that knows what they are doing to track down the problem.

OR!! You can replace all the black mica caps and likely be fine :)

Best is to use equivalent values of Silver Mica in their place, or you can even use cheaper ceramic caps.

Another very common failure with this pre is the phono amps like to crap out, because they too have the black mica caps of death!!
 
ManyMoonsAudio said:
There are a small handful of the black mica caps in that there preamp. I have also yet to see one of these preamps that did not need a full recap.

My money is on the mica caps drifted out of range and is causing funny things at the output. It may be intermittent or may not show up without being loaded!!

These caps being in range are absolutely detrimental to the stability of this preamp. It needs someone in there that knows what they are doing to track down the problem.

OR!! You can replace all the black mica caps and likely be fine :)

Best is to use equivalent values of Silver Mica in their place, or you can even use cheaper ceramic caps.

Another very common failure with this pre is the phono amps like to crap out, because they too have the black mica caps of death!!
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I just did some thread searches since I'd heard something about those black caps. Echowars coined the term black flag (that's what they look like). Other's opinions/expert advise that I trust have flat out stated that those caps can/will cause oscillation that will kill an amp DEAD.

Just wow!

Between the dreaded glue rot, dual cap cans, Vias (pass throughs), fusistors and this, Sansui is a fickle lover!
 
I read a thread and do remember someone mentioning the black flags. I am going to see if I can find the values on those notorious black flags. Also I will look to see if any electrolitics look bloated. Thanks again to all of you guys. Everyone's 2¢ is appreciated.
 
The electrolytics need changed. Plain and simple. They seldom get puffy in older gear. The tell tale is when you start pulling them and see that they have leaked around the leads.
 
ManyMoonsAudio said:
The electrolytics need changed. Plain and simple. They seldom get puffy in older gear. The tell tale is when you start pulling them and see that they have leaked around the leads.
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+1, I've never "seen" a cap that's gone bad but I've changed out a lot that were bad.

Well OK, there was one time when the speaker cross over caps were shrapnel.
 
Sounds like i will be replacing the black mica caps (black flags) and the electrolytic caps. Recapping is always fun to do when the boards are easily accessible. Any suggestions on what make of electrolytic caps would be a good match (nichicon, elnas or any others? Thanks guys, looks like I will start working on my cap list asap.
 
Sounds like I will be replacing the black mica caps (black flags) and the electrolytic caps. Any suggestions on which electrolytic caps would be best for this preamp elnas, nichicons, etc? I will start my caps list asap. Thanks everyone for your help.
 
Panasonic FM where you can get the values, then Panasonic FC for all else. Digikey. You can get the silver mica caps to replace the black mica caps. Mouser should have those.
 
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I use Elna simlac II wher available then Nichicon FG as second choice.
Mouser is stocking a good amount of Elna now.
 
No real need to use Silmic Caps in this preamp. Better to go with some high temp caps more than anything, as this preamp does not breathe well.
 
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An oscillating preamp taking out three power amps is an incredible scenario. Consider that power amps can be driven with just about any frequency at any level be that pulse, square, sine or impulse and NOT blow up. In fact, I can safely say I've never destroyed any amplifier with any type of input waveform regardless of the level or duration.

An oscillating power amp on its own is a different story.

The common denominator is of course this preamp, so get it to a tech who can put it on a spectrum analyzer/cro and find out what it is putting out, especially above 20kHz. In the meantime, check your tweeters are still working on the speakers you used.
 
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I was looking at my invoice for the repairs to the integra m-504 amp. They replaced output, driver, bias, pre driver, resistors, and current source trans. This I read right off from the repair invoice.
 
Thanks restorer-john. So you think I should hold off on the recapping and have it tested before I do any work to it then? Thanks for all your advise.
 
lopezluna said:
Thanks restorer-john. So you think I should hold off on the recapping and have it tested before I do any work to it then? Thanks for all your advise.
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It's a golden rule and restorer-john knows it well, 'fix the fault FIRST, then consider recapping/restoration'. ;)

It might be that you need to replace some capacitors in pursuit of an issue. However these should be measured hits on proven faulty components or tactical hits on likely candidates, not wholesale replacement.
 
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I will be taking it back to Fred at Classic Audio as soon as I can. Thanks guys. I will update you all as soon as Fred checks it out and finds the problem. Thanks to all of you guys again.
 
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