Recapping SX-950

Ah, that's more like it. To sum up, did you replace Q7 and Q5 or not? If not, those should be replaced as preventive maintenance.
 
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All I've replaced so far is Q2. I'm planning on recapping everything but the tuner board. How far should I go replacing transistors?

Thanks for your input Matt.
 
Here is a list of transistors that should be replaced as preventive maintenance

Power Supply Board (AWR-101)

Q5: 2SC1318: 512-KSC2690AYS
Q7: 2SC1318: 512-KSC2383YBU

Power Amp Board (AWR-059)

Q1-4: 2SA726: 512-KSA992FBU

Flat Amp Board (AWG-038)

Q5-6: 2SA726: 512-KSA992FBU

Equalizer Amp Board (AWF-011)

Q1-2: 2SA726: 512-KSA992FBU
 
I already ordered some 512-KSA992FBU when I thought the power amp had a problem. I think I ordered some extra so I should be good on everything but the power supply transistors.

I have a question regarding stress from the failure of power supply Q2. The output for the -51V was around -62V. Do you think there are other parts I should consider replacing because of the higher voltage? It looks like the-51V supply goes to just the power amp with Q3 and Q4 the only active components with direct connections. I measured the DC offsets and both channels were < 10 mV so I think the outputs are OK. The unit sounds good but I haven't pushed it hard since replacing Q2. Just headphones so far. I guess I'm wondering about the other transistors and diodes on the power amp other than the outputs.
 
The parts came in today. I replaced Q1-Q4 and the electrolytic caps on the power amp board. Powered up with a light bulb and everything seems to be OK. It seems the DC offset is a bit higher on the right channel. About 15 mV now.

Should I glue the 330uf caps to the board? The new ones are considerably smaller than the old ones. Were they glued because of the size?
 
No, the glue was for a production environment where the boards were stuffed, then wave soldered.

The dc offset is adjustable. It should be much more stable now with the input transistors upgraded. the target is 0.000v and the manual lists the procedure.
 
How sensitive are the adjustment pots? Does it take 1-2 turns to change the voltage a little, or will a little nudge cause a big change? Have you ever seen the need to change the pots other than if they're fried?

Thanks.
 
Normally with with these old pots it only takes a small nudge to make a big change because of the dust and dirt that have built up inside of them, so be careful. And yes, sometimes they need changed just because of how dirty they get or the resistance element wears down in one area. Sometimes Deoxit can clear the dirt and then it works just fine, but make sure it gets Faderlube afterward, otherwise the element will break down because the Deoxit takes out the lube that was already in there.
 
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So far I've replaced the caps and suggested transistors on the power supply, power amp, protection board and equalizer amp.

I've had a few surprises:

Power supply board:
C12 had a 2200uf@35V instead of 1000uf@35. (I'm going to order a 2200uf)
C14 had a 47uf@35V instead of 220uf@10V. (I replaced with a 220uf@35V)

Equalizer amp:
Apparently I have a different board than specified in the SM. The board number is AWF-011B. It looks pretty much the same except for a couple of 100uF caps in the middle of the board I also replaced. Anybody have an idea where I can get some info on this board?

Thanks.
 
C14 is used to slow the ramp up of the voltage for the function and speaker indicator lamps to avoid thermal shock. The 220uF is fine, all it will do is slow the ramp up a little more, 0.9 seconds opposed to the 0.183 seconds for the 47uF.

C12 is listed as a 1000uF on the schematic and the board layout, so I guess it's something that never made it into the service manual. Come to think of it, the SX-850 manual has C12 listed as a 2200uF, and it along with the 950 share the same board, so it might be an error in the 950 manual. The replacement for it is 647-UPW1V222MHD6
 
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Thanks for all your help Matt. I'm starting to understand specification of caps for different applications.

To update, I've changed the caps on the tone amp board. Not only were C13 and C14 2.2uf@25 instead of 10uf, so were C15 and C16. I also found that C29 and C30 were not installed but in their place were jumpers. There are isolation caps on the flat amp so I guess C29 and C30 are not necessary.

I've got straggler parts on order so I should be in pretty good shape after the next round of parts.

I was wondering if it's necessary to change the huge filter caps. I've found some 22000uf @63V but they're a bit pricy. I'm thinking I'll probably change them, but the old ones look pretty good and there is no evidence that they're going bad.

Dave H.
 
IMO, unless they are leaking, there's a lack of bass or a 60Hz hum that will not go away after a total recap of the power supply, which then points to the filter caps, I don't replace them. I do bypass them though, basically what that means is a 2.2uF 250v stacked film cap, 667-ECQ-E2225KF, is soldered across the terminals of the filter cap, and it takes over the filtering of the high end of the audio spectrum and makes a noticeable difference in that end.
 
Does the 2.2uf cap just make the high end cleaner? How does that work?

I thought the filter cans were mainly for 60Hz hum and initial filtering of the power supply.

Thanks.
 
Gmahoog, exactly what I was thinking. Will the 2.2 uf cap "filter" the hf in that it won't roll off the highs or to such a degree that it acts as the hf filter? Wondering what to expect if added this cap.
 
I investigated a bit and found an article that stated the lower value cap speeds up power delivery which helps audio circuit high frequency response. I believe it has something to do with the cap lowering the high frequency impedence so current can flow faster when needed by high frequency signals. I guess it kind of makes sense but I never heard of it before.
 
Parts are coming in today. I can't wait to get back to this. I have the flat amp next. Also bought some Deoxit and fader lube so I'm going to give it a good go over with the flat amp and tone amp removed.

I also order the 2,2uf bypass caps. I found a lot of info in the message boards. I guess all you have to do is look for awhile. Echowars had a good description but I'd have to look for it again to find a link.
 
e-caps are wound like toilet paper.

inductors are wound as well.

e-caps have parasitic inductance that does NOT short out (kill) unwanted high frequency crud at the terminals.

the 2.2uf caps are STACKED FILM- which are constructed like two books with interleaved pages (one faces right, the other left) and the bindings (hinge side??) are the electrical connections

result

DRASTICALLY reduced inductance, and removal of unwanted high frequency junk on the power supply lines.
 
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