Beloved Vintage Pioneer SA-6200 issues...

[shlauff]

Hi There,

This is my debut post here, but I've been reading everyones' advice on this forum for about 18 months now- I have built a couple of chipamps and am generally up for getting stuck in where I can... but I'm far from understanding everything, which will come in time i hope!

I've had a Pioneer SA-6200 integrated amp for about 10 years which dates to the early 70's I believe, and I love it- nothing has ever gone wrong, and it sounds great... until last week!

Actually this problem had shown it's ugly head a few months back but it only happened once, then went away... When I power the unit on now, almost instantly a very loud crackle is pumped out, regardless of volume setting.

Not wanting to pester the gurus on this bored I got the old screwdrivers out, popped the hood (built like a tank this thing) and ordered replacement Smoothing caps (there is no hum with the crackle, so i figured it wasn't the power supply, but as i say i may well be wrong!). They arrived this morning and I got the iron and swapped the caps...

Turning the unit on again crackling started- but only for a second or two- then stopped... ok!? After connecting a source the amp was working fine, for 10 minutes (and the volume was fairly high, figuring heat might be a factor, but as i said the original problem was from power up)- then it did it again, drivers on test speakers pumping away. I powered it off then on again and have been soak testing it for well over an hour with no problem.

I know it's tough not seeing the thing but has anyone any idea what the trouble could be? I've definatly improved the issue but it is obviously still there in some form or other. I would have thought it was either the Caps or not!? I'm really hoping it's not the transistors or anything...

Any help would be greatly appreciated...

[filholder]

Pumping speakers like that sounds to me like a bad powerline stiffening cap in the preamp.

I had an issue recently whilst building a guitar amp, the power amp modules were new class-D affairs and i knew they were fine. The preamp was of my own design but loosely based on something i found on the net. When powered up, the unit would work fine, then occassionally is would loose all control with the speaker pumping in and out for even if the signal was stopped.

I thought it might be something wrong in the power amp, but it turned out to be a the fact i hadnt uprated the caps sizes enough in the preamp from the original design i had been looking at.

I had 12- 0v with a 100uf and -12v to 0 with 1uf, if wasn't enough and the virtual ground was moving around since the caps couldnt hold it.

Now it your amp the old smaller caps it the preamp may have gone so far out of value that something similar is happen, as a strong signal come through the ground starts moving around cos the caps are so far from there original value.

Anyway thats my take,

Phil

[sakis]

to an amp like that there can only be three things ..... ( no matter if this will take weeks to find )

japanese manufacturer at this time never used precise resistors like 1% or metal film or even 5% but the thing is that the resistors inside actually worked !!!!!! but for how long nobody knows .....very possible that some of them having other values than specified since they ve been working for so long exposed to heat also for so long .....

the same apply for capacitors of the all machine but about ten times worst most of them if not all should be replaced

and third that most of switches must be oxidised or dirty after all these years ...so this is where you focus .....

starting from the secondary power sup ....recap everything ....then amplifier boards ...and goes on ....

small tip :
in japanese products all this is like happenig to families meaning that if you find one capacitor 220mf/25v doomed then it seems that all the capacitors of the same rate and brand existing inside eventually will need to be replaced ....

almost the same for resistors ......

after all that and some testing ( for correct idle and offset ) you will actually have not only working ampa but also kind of updated and very possible that sounds a hell of a lot better than it did before the small repair

regards sakis

[Bigred]

First step would be to better isolate the problem if possible. Does it crackle/pop in both channels or one? I believe the 6200 has pre out/power in jacks so you could isolate even further to see if its limited to the pre or power amp section also. I doubt its the problem but I'd agree that the integrated could definitely benefit from a Caig dexoIT treatment: all the switches and potentiometers. A complete recap of the electrolytics would be on my list too, but especially the power supply or any near heat sources. The differential pairs have been known to cause some intermittent noises (Q1-4).