Pioneer SX-1050 intermittent sound cut out

[Planetary]

Hello everyone!

I am new to the forums and looking to learn more about receivers and to repair my newly acquired Pioneer SX-1050. I love this thing, however the sound cuts out randomly for a random amount of time. It sounds like the voltage inrush delay relay (I think) that clicks on after you power on the unit. I found an old thread on this but am still a bit lost, http://www.diyaudio.com/forums/soli...38-random-no-sound-output-clicking-relay.html . I took the lid off the 1050 and the click sounds like its coming from around the transformer area. From what I hear this is a fairly common problem but I haven't found much of a guide on it. I have a service manual for the 1050.
Help is greatly appreciated!

Alex

 

[bob91343]

Open the unit and measure the output voltages from each amplifier. If you can reset the center voltage to zero with the adjustment referenced in the manual, it should solve your problem. See Paragraph 10.3 in the service manual.

 

[east electronics]

and or take a look for leacky capacitors in the protection area or the all amplifier ....

make sure that the trimmers you adjust are clean and in good shape cause if not this is dangerous

 

[EchoWars]

If the relay is cutting out the sound, it is the speaker protection relay, not the soft-start relay.

You need to measure and monitor the offset at some point before the relay on both channels to make sure that the cause of the relay opening is not an issue with the DC offset on one of the channels triggering the protection circuit. If that looks OK, then you almost certainly have aged capacitors in the protection circuit, and probably a weak relay driver transistor.

 

[Planetary]

Thanks for the help! I have checked the caps and there are some leaking. The larger two caps on Power supply assembly A, 220uF 80V, and the large one on Power supply assembly B, 2200uF 25V. I assume I should replace these before I proceed to adjust anything, right? Where would a good place be to get quality replacements? I have not taken measurements of the DC balance on the both amp channels yet.

Thanks

Alex

 

[Planetary]

Okay, I replace the caps using real nice power Nichicons. It still clicks off. I checked the DC balance and both channels read, 0.01 V and sometimes jumps to 0.00 V. Do I need to adjust the voltage pots? Whats next?

Thanks

Alex

 

[Planetary]

I now realize that the protection relay is opening. The caps look fine, though I don't have a multi-meter with capacitance metering. I have the schematics of the protection circuit assembly. I am not sure which is that relay driver transistor. Does the DC offset of 0.01 V (jumps to 0.00 V and back to 0.01 V intermittently) need to be set to 0.00V? How do I test the transistor and which one?

 

[Planetary]

And for my 4th post in a row...
Oh man, EchoWars, I am glad I read your dc offset on audio karma. I see that these offsets are real low. Duh. I measured 4-7mV which is 'damn good', correct. Not sure what to do now. I am seeing if I can use a cap meter mainly for the protection board. I suspect the relay driver transistor is the one feeding into the relay, correct? There are 7 transistors and 6 electro caps on the protection board.

Thanks.

 

[Planetary]

Well I decided to take the unit to the local shop, which is an impressive place, to get it fixed. It turned out it needed a dozen or so transistors replaced. I used deoxit and faderlube to clean the pots and now it works fine now, however I plan to repcap all the power caps in the power and protection circuits because the speakers pop when the unit is turned off. I stopped using it until I do this. I also plan to reset the idle current and dc offest.
Thanks for the help.

 

[pioneerlover]

i don't know if your still active on this site but i have had the same cutting out problem with my pioneer, and i would like to know how much it cost you to get it fixed at the shop you took it to.

 

[stocktrader200]

Replace the capacitors on the protect circiut IC as well as the small ripple cap
I have a sx 3700 that had the same problem.
just to be sure , check the DC at amp outputs for levels greater then 750mV
ideally it should be close to zero

 

[bx19]

Quote "It turned out it needed a dozen or so transistors replaced."

Why was so many transistors failed at one time?

 

[rsavas]

Probably changed the transistors as part of a reverberation effort, changed them even if they were working, same as a changing the ecaps.
audiokarma site has lists of parts to change, with Mouser part numbers to make it real easy. The hard part is actually carrying out the task, but there lots of help their.