SX1010 "Pops" when shut down after recap.

larryderouin said:
Add a 1n4004 between pin 9 (anode) and pin 10 (cathode) on the protection board. Keeps Q7 alive longer by preventing backfeed from relay coil when the field collapses at shutdown. I would go back over the protection board, sounds like it's not tripping the relay fast enough.
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I am going to add this note to my service manual. I wish the guy who owned this wasn't in such a rush to take it home.
 
markthefixer said:
pop on power-off means the protection really isn't )working.
don't have a scat, check for a733(ebc)vs a733c (ecb) in the "short out timing cap stage"

classic presentation...
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All except I didn't swap out any transistors, and it was working before I recapped the protection board. More notes for the service manual.
 
EastPoint said:
Those caps are all uniformly terrible and desperately need to be replaced. Same with most of the old transistors. Use Wima film to replace the smaller electrolytic caps and KSA992/KSC1845 to replace the transistors. The SX-1010 is a great receiver, it deserves a full rebuild.
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I had my very own SX1010 about a decade ago... someone offered me $700 or $800 for it and I foolishly let it go.
 
pop on power-off means the protection really isn't )working.
don't have a scat, check for a733(ebc)vs a733c (ecb) in the "short out timing cap stage"

classic presentation...
Click to expand...
the timing cap isn't being deliberately discharged by the power being turned off.
That means that DC protect with the back to back caps ISN'T WORKING.
It ALSO means that the over current protect for each channel ISN'T WORKING.
This is one serious situation.
 
painttoad said:
87,000 in stock here


36,000 here

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Thank you.

I found suddenly DigiKey has restocked them. Same price. Same with the 992's.
This time I did buy hundreds, on tape. I think it came out to $22 for the 1845's and $28 for the 992's by 100 quantities.
markthefixer said:
the timing cap isn't being deliberately discharged by the power being turned off.
That means that DC protect with the back to back caps ISN'T WORKING.
It ALSO means that the over current protect for each channel ISN'T WORKING.
This is one serious situation.
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You are quite correct.
I will have my friend bring his receiver back to the shop for repair.
 
opening up & closing the 7vac lighting fuse and triggering protect on / off is a quick n easy test of that area of the circuit
 
Maybe to monitor power on? When the lamp power goes off it will discharge the cap holding the relay on and prevent a power off thump at the speakers.
 
HPMguy said:
Maybe to monitor power on? When the lamp power goes off it will discharge the cap holding the relay on and prevent a power off thump at the speakers.
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EXACTLY !!

winner winner chicken dinner.

things go nuts as the various DC voltages decay as their (storage) capacitors drain, with no restorative AC voltage input.
So sensing the lack of AC is the best early warning of the power switch being turned off.
So we get the speakers and our ears out of harm's way.

other inputs are also combined in that stage - overcurrent protect (one diode) as well as DC voltage to the speakers (two diodes).
 
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markthefixer said:
EXACTLY !!

winner winner chicken dinner.

things go nuts as the various DC voltages decay as their (storage) capacitors drain, with no restorative AC voltage input.
So sensing the lack of AC is the best early warning of the power switch being turned off.
So we get the speakers and our ears out of harm's way.

other inputs are also combined in that stage - overcurrent protect (one diode) as well as DC voltage to the speakers (two diodes).
Click to expand...
Thanks to all who helped with advice.
C5, a 4.7uf cap, was mistakenly replaced with a 47uf during the recap.
This had the effect of extending the de-energizing period of the relay by an order of magnitude.
Again, thanks to all.
 
tutor_turtle said:
Thanks to all who helped with advice.
C5, a 4.7uf cap, was mistakenly replaced with a 47uf during the recap.
This had the effect of extending the de-energizing period of the relay by an order of magnitude.
Again, thanks to all.
Click to expand...
Yep, that significant difference in cap value in that application would throw off the R/C timing constant considerably, as you discovered, tutor_turtle ! Those decimals can be pesky if not paid attention to !

Glad to read that you backtracked and found your recap error and restored the proper timing.
Enjoy the music.
 
tutor_turtle said:
Thanks to all who helped with advice.
C5, a 4.7uf cap, was mistakenly replaced with a 47uf during the recap.
This had the effect of extending the de-energizing period of the relay by an order of magnitude.
Again, thanks to all.
Click to expand...

I'm just going to pop in and say this is why I love this community! I did the same damn thing. Reading this, I knew exactly what I had done. You save me an afternoon of frustration.

Curse my old eyes... lol
 
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