amplifier clicking in and out of protection

[theblackknight]

awhile back i posted about my setton BS-5500 amplifier.

it was clicking in and out of protect, so i checked inside and it had a pretty badly leaking power supply cap.


I changed all 4 caps 2 days ago, and soldered in new $20 ones with the correct values, correct way, etc etc etc.

I then measured dc-offset which was ~35mv a channel.

i even cranked it WAY UP for a while almost to clipping earlier today, and had no probs at all.

and then after letting it idle for about an hour, it started clicking in and out of protect again!!!!
what could be wrong??? i fixed one OBVIOUS problem, and now it's still not working?????


please help me with this !!!! i really appreciate it!!

thanks,
Henry

[theblackknight]

I just finished letting it cool down for about a half hour, and and then powered it up again and now it stayed out of protect for a couple minutes.

I am thinking that maybe:

1. it goes into protect more often when it's warm.
2. i may have been ruining a new cap by using it these past couple days--maybe something else is causing the cap to go bad, and when the cap starts to go bad, it goes into protect more often.

also, the amp does not run excessively hot or cool, so the bias current is probably not out of line.

[EchoWars]

I got your PM through AK, but since you started the thread here, here is where I'll answer.

First off, I know nothing about this amp. I wanna make that clear. But, if it uses some sort of a more or less conventional protection scheme, there is circuitry to mute the signal on power-up and power-down, and circuitry to monitor the output DC voltage as well. Circuits such as this generally control relays which interrupt the signal to the speakers when a fault condition is indicated.

You said something about the 'left' side going into and out of protect. Usually there is only one protection circuit for both stereo channels...if a problem is indicated on one channel, both channels are disconnected from the load [speakers]. If your amp has only one protection circuit, and you are losing only one channel, then the problem is not likely in this circuit.

Bottom line is I'd have to see some schematics before I made a more educated guess as to what the problem could be or to tell you where you might look. But if the amp has separate circuits and relays for each channel, it may be something as simple as some aging caps or weak transistor in this circuit.

[djk]

There is either DC on the output causing the relay to trip, or the timing capacitor in the relay circuit is dried up.

The second is more probable.

[gmphadte]

Old amp working intermittently normally means dry solder problem.
Even the output transistors become open inside the package on heating, but it is not in this case.

Gajanan Phadte

[theblackknight]

EchoWars:

the BS-5500 has a true dual mono design, with a metal bar that runs down the middle of the amp entirely separating the two sides. thus, it has two power switches, two speaker selectors, two transformers, two protection circuits and relays, etc etc etc.

unfortunately, it is extremely rare--I have searched numerous audio forums, and asked just about everywhere to try to locate a service manual or schematic. I know of about 5 BS-5500 owners worldwide, a few are setton experts. even they do not know of a manual or schematic anywhere.

like sansui's it does have the "block diagram" printed on top of the case. I can post a pic of this if you want. amp nudies are below if that help at all.

let me know what you think i should do next!

also---I have 2 of these amps--the other works very well, but the offset measures 50mv/channel. after i changed the PS caps in the "broken" one, while it was working it sounded and worked much better than it ever had, and still proformed considerably better than the now only-working one(with 50mv/channel offset). but, even though it proforms so well, it clicks!



djk: i am certain that 35mv/channel would not cause the protection to engage. i had another pioneer amp (SX-939) that i used for years and the offset was always over 50mv/channel, and i never had a problem.
I do not have a clue what the timing capacitor should look like. below are pics--see if you can point it out so i can test it.



gmphadte: the amp is almost mint and i cannot see any solder problems or bad connections.

thanks for everyones help!!!
Henry

you can see the relay on the board in the second image. i would be happy to post more closeups if needed. also, the metal bar that separates them runs through on the underside, which i can also get a pic of if needed. there are no wires in common between the two sides on the top.






here is a pic of the two amps with a tuner on top when the amp worked:

[theblackknight]

For some reason, my pictures do not seem to be working/linking to this page. Instead, a small red "x" appears where the picture is supposed to be. Do any of you know why?

Also. is there a way I can edit my posts? I forgot to spellcheck them and correct them like I'm supposed to, and the only one I that has the edit button is this one that I just posted.

Let me know!
Thanks!
Henry

[djk]

I can see the photos.

Edit only works for a half hour, and only if no one has posted after you.

[theblackknight]

yep, they are working now. Wonder why I couldn't see them before?


OK, back to fixing the amp!

[EchoWars]

Step #1: Recap the boards with the relays on them.