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SX 950 power board issues, and issues down stream

Rathwine said:
I have both transistors. I can check fuse holders. How do I check the pop with the jumpers out? Does the headphone jack still work then?
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Reconnect the speakers. Do you have a sacrificial test pair? The jumpers separate the preamp section from the power amp section. If it still pops you know the problem is not in the preamp section.
 
While removing the fuses one of them, second from the back, the clip just fell over on one side. This is on the after fuse end, not power end.

Are those available any longer?
 
Rathwine said:
While removing the fuses one of them, second from the back, the clip just fell over on one side. This is on the after fuse end, not power end.

Are those available any longer?
Click to expand...
If it is a clip that is soldered into the board Mouser carries similar clips.
 
The fuse clip that broke, was its other end connected to an orange wire?
The orange wires feed the rectifier that powers the amp circuits before the output stage.
The green wires power the lamp circuit's rectifiers.
They are both taps on the same transformer winding.
 
merlynski said:
The fuse clip that broke, was its other end connected to an orange wire?
The orange wires feed the rectifier that powers the amp circuits before the output stage.
The green wires power the lamp circuit's rectifiers.
They are both taps on the same transformer winding.
Click to expand...
Green wire
 
merlynski said:
That may well have been your lamp issue.

@petehall347 Good call :thumbsup:
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It is. I tied it up with a rubber band, and lights are steady and nice. Interesting note, when that fuse disconnected the protection circuit went on. I had to find a way to make it stay working to test the pop.

It pops without the preamp out/in jumpers.

Another diagnosis. Now I need to add another fuse holder to the list to order.

Also the pop took a long time with no amp running.
 
That means the problem is in the left channel power amp. If you were planning on rebuilding the power amps that probably will resolve it. It usually is the differential amp section transistors (Q1, Q2) but could be any of them. Do the electrolytic caps as well. Consider changing C1, 2, 3, 4 on the power amp to film caps. Also C1 & C2 on the protection pcb to film.
 
merlynski said:
That means the problem is in the left channel power amp. If you were planning on rebuilding the power amps that probably will resolve it. It usually is the differential amp section transistors (Q1, Q2) but could be any of them. Do the electrolytic caps as well. Consider changing C1, 2, 3, 4 on the power amp to film caps. Also C1 & C2 on the protection pcb to film.
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Ok will do. I will see what I already ordered and see what I need to change them to.

I'll check the list tagged earlier also.

I planned on redoing all of the major caps and transistors anyway. Just wanting to do it a bit at a time and test so I don't cause new problems.

Thanks a ton .
 
merlynski said:
That means the problem is in the left channel power amp. If you were planning on rebuilding the power amps that probably will resolve it. It usually is the differential amp section transistors (Q1, Q2) but could be any of them. Do the electrolytic caps as well. Consider changing C1, 2, 3, 4 on the power amp to film caps. Also C1 & C2 on the protection pcb to film.
Click to expand...
Of those 6 caps, I already have film for 4 of them. C-3&4 on power amp and c1&2 on protection.

I just need to get the 2.2uf ones in film for c1&2 on power amp board.

For the q1&3 and q2&4 on the power amp board I have 6 left to find the best matches.
 
Rathwine said:
I found a pair at 368 and 374. Another is 364 and 365. Last set are 343 and 349. I thin these all would work.
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Yes, the biggest reason to match them is to get good dc offset in amps that don't have an adjustment, since this one does adjust . . .
 
Parts are ordered. I will see what I can work on until they arrive. I just do not feel like changing caps to change them again when the new ones come in next Tuesday.

Thanks Troy.
 
Ok, I got the new parts in. Installed new caps on the power supply board. Triple checked polarity. Put it on DBT, and checked voltages. Everything looked good. Then after retesting I heard a click (protection mode), and my voltages on pin 13 14 and 15 dropped .

New voltage on DBT
13. -2.5
14. -13
15. -4.1

I am guessing I have somehow lost q6 again, maybe I shorted pins while testing.
I don't remember it but it is the only thing I can think of.

Not sure what else may be gone. Any ideas?

Thanks. Troy.
 
merlynski said:
2.2µF 100vdc MPET
667-ECQ-E1225JF3 5mm lead spacing
667-ECQ-E1225JFB 10mm lead spacing
Click to expand...
Ok, installed all caps and seemed fine. Found one cap was backwards when I found power was wrong. Power supply c-20. I fixed it, and retested. Seemed all good but I must have brushed 2 posts while testing with the multimeter, and I heard a click as the protection circuit engaged. Now power is all wrong on pin 13, 14, 15.

13--2.5
14. -13
15 -4.1

So I changed out q2 and q4 in case. I do not have a spare for q6 as we changed that last week.

From the negative terminal of c-11 I have -46.5v

That carries to the collector of q-2 and seems good there. But everything after the collector seems wrong.

Q2 emitter- -11.2
Q2 base-. -11.8

Q2 base is fed from q4 collector which is -11.8
Q4 base is -2.8
Q4 emitter is -2.3
Any suggestions are welcomed.
Notes on testing, all done with dim bulb tester.
Protection relay does not release
I have done all of this with the jumpers from pre out and in removed
Thanks.
Troy.
 
First cover all but the very point of your probe with heatshrink or tape so it won't do again what we have all done in the past :oops:.
Pull Q6, it could be loading the regulator, then 6-way test it. Leave it out for now. Did you order more? I buy small transistors by 100 lots, they cost less and are on hand when I blow them up.
I would say Q2 and Q4 toasted, and may have taken ZD12 (13v) with them. The emitter of Q4 should be higher, but the emitter has to come up for the current supply for it. Replace ZD12 if you have one.

"Protection relay does not release" Actually the Protection relay pulls in when the unit comes out of protection, either at power up or after a fault clears. It releases when going into protection or at power off.
 
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