Pioneer SX-650 Popping Rushing Sound Right Channel

ILikePioneer

ILikePioneer

Riddle Me This!
Hi, I got a 650 that did not work, I replaced all the caps and transistors on all boards, I deoxed all the switches and controls, the unit passes the dim bulb teat, no shorts. When powered to the wall socket It turns on fine, the relay clicks but you can immediately hear feedback from the right channel even with no volume. When the tuner is playing I'm getting a rushing, popping sound(like a bad transistor). Relay clicks on and off during these symptoms too. It does this on all functions, the tape monitor switch does not effect the feedback at no volume. I got the recap list from UncleBambi's post and pieced together the transistor replacements from numerous posts from a few members here. I have posted pics of the power amp board with the transistor replacements that were used. Any suggestions why this is happening to the right channel would be very helpful..

Thanks

On the other power amp I replaced the 2SC1438's with KSC1845's
 

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short the amp inputs, pins 10 and 25 (confirm that) to ground and see if it continues.

there's no idle or offset pots to mess up in these amps, and only two transistors (on is a dual).

There are 2 ic amps feeding the passive tone controls, so there isn't much more to it.

you can trade parts between the channels and when the symptoms follow a part, there you are... (look at d1,d2 as well)

cross your fingers it isn't the module.
 
Both pins 10 & 25 to ground? Also are my transistor subs ok?
If it is the module wouldn't I get a dead channel like on the SX-780's with the Darlington power pack?

Thanks Mark
 
If an STK module fails, one channel would likely have no sound or highly distorted sound. If noise is being generated in a junction in the module, the "gray" noise you are hearing could be produced.
 
Watthour said:
If an STK module fails, one channel would likely have no sound or highly distorted sound. If noise is being generated in a junction in the module, the "gray" noise you are hearing could be produced.
Click to expand...

I'm thinking the transistor replacements that I used are not suitable replacements?
 
The replacement for the 2SC1384 could have been a KSC2690A instead of the KSC2690. Ratings on the "A" version are quite a bit higher.
 
The KSA940 may be marginal in place of the 2SB507. The replacement is only rated at 1.5A Ic compared to 3A on the original. A MJE15033G would be bullet-proof in that spot.
 
Watthour said:
The KSA940 may be marginal in place of the 2SB507. The replacement is only rated at 1.5A Ic compared to 3A on the original. A MJE15033G would be bullet-proof in that spot.
Click to expand...

Made the changes to a few transistors through recommendations, now I'm getting loud feedback through both channels with volume all the way down as soon as relay engages. It will do this until the relay trips out, then comes back on with the same feedback. This is a head scratcher, any help would be very helpful and appreciated. All transistors were checked and rechecked for proper seating.
 
Understanding that the replacement devices will almost assuredly have a different E-B-C lead arrangement, are all the connections double-checked and verified?
 
Watthour said:
Understanding that the replacement devices will almost assuredly have a different E-B-C lead arrangement, are all the connections double-checked and verified?
Click to expand...

Absolutely Watthour, Checked and rechecked leg placements, checked also for capacitor placements, all ok..:scratch2:
 
I would have presumed that they were done properly, but it doesn't hurt to ask. We never know who might be reading this in the future.

By mentioning "loud feedback" are you experiencing what might be described as static, hiss, gray noise, or actual signal or program sound? Does this occur with any particular program source selected? No source? Regardless of tone settings?
 
ILikePioneer said:
Made the changes to a few transistors through recommendations, now I'm getting loud feedback through both channels with volume all the way down as soon as relay engages. It will do this until the relay trips out, then comes back on with the same feedback. This is a head scratcher, any help would be very helpful and appreciated. All transistors were checked and rechecked for proper seating.
Click to expand...

the answer may well be here .. which transistors did you change to make the problem shift to both channels ?
 
Watthour said:
I would have presumed that they were done properly, but it doesn't hurt to ask. We never know who might be reading this in the future.

By mentioning "loud feedback" are you experiencing what might be described as static, hiss, gray noise, or actual signal or program sound? Does this occur with any particular program source selected? No source? Regardless of tone settings?
Click to expand...

As soon as the unit is powered on and the relay clicks with volume at zero you can hear a loud staticky sound, at first it was in the right channel, now it's in both. When you adjust the volume you sometimes get audio from both channels then pops and back to static, then the protection relay engages. It happens in all sources regardless of tone settings.
I also checked the transistor leg placements again and all look good.

Thanks for the help
 
Just a WAG, but having experienced a similar set of symptoms in one SX-750, I'd be looking at the power supplies, including connections and grounds.
 
petehall347 said:
the answer may well be here .. which transistors did you change to make the problem shift to both channels ?
Click to expand...


Q11-2SC1647 changed to KSD1616
Q12-2SC1647 changed to KSD1616
Q14-2SC1647 changed to KSD1616
Q13-2SA823 changed to KSA992
Q6-2SC1649 changed to KSC1845
Q5-2SC1649 changed to KSC1845
Q15-2SC1384 changed to KSC2690

all transistor leg placements have been checked and rechecked..
 
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