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Pioneer sx780 noisy right channel

i changed the darlington of the right channel and for a moment the noise went away, but it returned.
the weird thing is that when the noise starts I turn up the volume and the noise goes away. What else can I try?

thanx!
 
and it only affects one channel?
and if so, why does it affect a channel?
change it and try?
I was going to change transistors Q25, Q20, and Q19
I change them too?
 
Last edited:
guille go said:
and it only affects one channel?
and if so, why does it affect a channel?
change it and try?
I was going to change transistors Q25, Q20, and Q19
I change them too?
Click to expand...
The relay has four sets of contacts, two for each channel, in parallel. If the contacts on one channel are damaged and the other channel's contacts are not damaged, it will only affect the channel with the damaged contacts. The other channel will be normal. The prime indicator that it is the relay contact problem, is that turning up the volume cleared up the noise. The higher voltage breaks down the damage on the contacts temporarily, letting the signal through. Cleaning the contacts will clear the problem for a short time, but once they are damaged they will not last long. Replacing it is the best option for a long term repair.

Q25 is the transistor that get the hottest, and sometimes the solder connections on the board are damaged by the heating and cooling. Reflowing the solder joints repairs the cracked solder. Q20 and Q19 don't get quite as hot, so they don't have as much of a problem. Replacing all three is a good idea. Adding a bigger heatsink, especially to Q25, is a very good idea, also.
 
I hope I can help someone, it seems that the noise is gone by changing q20 q25 and q19, I measured the voltages in the darlington packs and they arrive ok,I also bought a relay, just in case.

also do a better cleaning of all contacts.

I'll keep you informed

thanx a lot merlynski
 
the noise in the right channel returned, even after the service, I swapped the darlingtons as I said, and the noise remains on the right side

could it be caused by the speaker selector (A or B) ???

as it does not happen all the time I cannot detect exactly where it comes from, if it is a button, connector or something else
 
guille go said:
I saw those replacements of the stk-0050 in some posts , but here in Argentina I don't get them, but I saw here a Chinese versions of the stk-0050, maybe I bought some for replacement.
I have been testing the sx780 for 3 days and the noise did not return, later I will review the darlington heatsink compound,
could you tell me the theory why only one channel comes out with noise?
Maybe that poor power supply affects the darlington of the right channel because it is more deteriorated

Thank you very much for your help, I appreciate it very much
Click to expand...
hello

but we have here in Brazil, if you need i can help you.

Gracias!
 
Did you replace the dual transistors? There are two 2SA979 and I think two others as well. There are two 2SC1775 in the middle of all the dual transistors—those should be replaced too.

What I would do is replace the 2Sc1775s with KSC1845s. If that doesn’t solve it, then try swapping the dual transistors side to side and see if the problem switches sides.
 
could it be caused by the speaker selector (A or B) ???

It seems that in the service they changed those transistors
 
Eastpoint
the transistors you told me are recently soldered, they don't look like new components, maybe I'm wrong. Could it be that they have only been removed to make a measurement? If so, I change the 4
the 2sc1775 (2) and 2sa979 (2), if so , i will change the 4

It is a difficult fault to find, it does not always happen, I can be listening to music for hours and no noise is heard, and it can happen as soon as I start the equipment, and I cannot duplicate it in any way to know where it is.
re clean the contacts several times, the speaker selector a and b, the volume knob etc.
 
heat and or cold will often show up failed components .
on another note any chance of you posting an audio file of the noise ?
 
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