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SX-950 Recap

Brad Helms

Brad Helms

New Member
Finally got all the capacitors from Digi-Key still waiting on a couple transistors which has been about eight weeks. Thought I would get started on my project and ran into something I’m not familiar with. Three pins on a capacitor the C 12 in the manual calls for 1000 µF 35 V capacitor but the one that it was in there was a 2200 µF 35 V and also had a third pin take a look at pictures what to do? Replace with a two pin as I don’t see the NC pin hole leading to anything why does it exist? Or do I need to replace with a 2200 µF 3 pin cap? Help
 

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The third pin is a dummy pin just to add mechanical strength and to prevent inserting the capacitor backwards (before the late 70's early 80's a lot of these boards were populated by hand).

I would replace it with a 2200uF 35V cap, likely a running change during manufacture unless you think someone else randomly stuffed it in there during a repair.

You don't need a three pin cap there for a re-cap, but you will probably need a four pin radial can cap with one leg cut off to fit the pins -- likely those are spaced wider than the plus and minus on a snap cap. Four pin caps are 15mm? lead spacing (I think) and snap caps are 10mm, so it won't physically fit unless you bend the legs and maybe solder on some extender leads. Can be done, but a drop in is always better.

Select the capacity, voltage, and then "4 pin radial can" option on either Mouser or Digikey to filter for a four pin cap. I seem to remember a lot of them at that capacity, it's 10,000 uF and up where they get scarce and I need them for a couple things I'm working on at the moment.

I'm guessing this is in the power supply since most people start there, so use a UPW or UKG series cap if they have one.
 
Thank you HPM guy. You guessed it I’m starting with the power supply board sorry I didn’t include that. I thought the third leg was for support as I didn’t see the lead in the board going anywhere. I just wanted to make sure... Everything leads me to believe it is original so I will order a 2200 µF even if the manual calls for 1000 µF.
 
I upgrade to 2200 uf 50v, and use Panasonic FC or Nichicon PW. A few pioneers have a 1000 uf in there but most use the 2200.

The third leg is a dummy lug and you can just close that hole up with a little solder.
 
I recapped the PS board except for C-12 (2200µF 35V) which I reinserted to test because I only had the 1000 µF 35 V cap replacement per manual. Results of test run same as before relay popping in and out. Thinking about moving on to protection circuit board recap while waiting for 2200 to be delivered. Thoughts? BTW - Tested 2200 and it was bouncing all over 1800.
 
Sure, do the protection board, but make sure you get the transistors there too—those are probably causing your problem.
 
Check the voltages on the protection board against the service manual, this may give you a hint as to where the problem is.
 
Do I dare take it off the DBT to test the voltages as I have found the voltage to be under what they are supposed to while on DBT making it difficult to determine issue. Are you guys having issues with transistor availability? I’ve had transistors on order for over eight weeks Getting pushed off each month
 
Was this functioning properly before the re-cap started? If so, and you do indeed have a dim glow after the main caps charge, I would go off the DBT if needed. However, you can figure that the supply voltages will the low, but anything less than that should be pretty close,

If it's not going out of protection I would leave it on the DBT and look for widely divergent voltages -- for instance, high DC on the output causing the protection circuit to shut things off. Voltages on the test points of the protection board should be close to what is in the schematic except the main power on "signal" -- not familiar with that circuit, someone else with more experience will pop in sooner or later.

If you find a voltage that is positive instead of negative, or some volts instead of zero, trace back through that part of the circuit to find out what's "broken".

I have a Technics SA-310 I'm working on right now that has no output on one channel. Appears to have internal circuitry in the STK module that shuts off the amp circuit if the ouput exceeds normal without muting the other channel, and I found 2V on the input of the power amp and on the output of the voltage amp section -- waiting on parts to pull it all apart again to test the bias diode and current gain transistor on that little subsidiary board. Either the diode is bad switching the transistor on, the voltage amp is shorted (it's an IC in this receiver) or the transistor is leaking badly. Known problem transistor, too. Same story in my Yamaha R-700 -- in that case I had 35V all over the place on the STK for that channel plus a smoked resistor, and 35V (or -35V, don't remember) where I should have had zero in the protection circuit from the ouput. Sure enough, the STK is shorted to the rail supply internally.

This is what I mean -- a voltage far off from what it should be rather than just lower on the rail voltages is a clue for where to look.
 
I used Nichicon snap-ins for C10, C11, and C12 and the lugs fit perfectly. LKG1H222MESZBK and LKG2A681MESZAK. Not high temp, but high ripple handling and low power loss.
 
LKG is a good series for that application -- high ripple capacity and low resistance/power loss will keep them cooler so high heat capacity is less of an issue.

I think what causes electrolytic's to leak is high ESR and high ripple, hence overheating. Higher heat rating in a spot that shouldn't be getting hot won't help with the caps are heating up on their own.
 
Thank you gentlemen... The receiver was tripping from the get go. The DBT had a bright glow then to dim and protect popping in an out. So I haven’t found prob yet I do however have a suspect Q7 transistor that I have been waiting on for eons. Thank you for the advice I will take readings to see if something jumps out. Cheers and Happy Memorial Day
 
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