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SX-636 no longer working properly after using DBT

fromnowon said:
That's ok. I think there are pros and cons . . . I thought it was a lot of work to reattach - you'll find out probably! :) You'll know they are well-attached and good connections this way though and it's great for working on it, to have it removed.

Good luck re-soldering! If you have any questions about what pin a certain color wire goes to etc. I'd be glad to check mine, it's sitting right here with the covers off still.
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Thank you! I'll probably have to take you up on that when I inevitably lose a wire somewhere ;) We'll put that off as long as we can, though :) I'm curious about replacing the pins with screw terminals or something similar. As long as they fit properly, it seems like that would make it much easier to maintain!
 
Unfortunately the heat sink compound has been delayed until tomorrow, but I thought y’all might enjoy this info that I found in my multimeter’s manual :D
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I thought I knew Chinglish well but this is a new one! Or maybe they watched too many episodes of Magnum, PI...
 
Anyone have any advice on cleaning the sticky stuff (solder flux?) off of PCBs? I've tried scrubbing it with a toothbrush and 70% isopropyl but that doesn't seem to do it.
 
After scrubbing it with the alcohol it needs to immediately be gently wiped with a paper towel or similar to lift the flux. Try using 99% or denatured alcohol, probably pretty hard to get now days. 70% should work, keep in mind that solution has 30% water in it. There are more pro ways to accomplish this, google/YouTube should show see good demonstrations.

Process usually needs to be repeated, clean the tooth brush with clean alcohol before attempting again as it holds the flux and just starts spreading it around again.
 
So, Amazon lost the heat sink compound that I ordered and I’ll need to find a replacement. Is Arctic Silver 5 ok for this application? It’s not conductive, but it does have silver particles in it. My alternative is to get some Dow Corning 340 on the ‘bay, but that would mean more waiting. I’m also planning to stop by the hardware store tomorrow and see if they have anything that might work.
 
I just ended up ordering a tub of Dow Corning 340 from eBay that should be here by next Tuesday. In the meantime, would it be catastrophic to power it up for a few minutes at a time with a heatsink but no compound on Q3 just to test it out? If I can verify the power supply is working then at least I'd be able to move on to rebuilding other boards while I wait for the compound. Anticipation is hard :oops:
 
voxswain said:
In the meantime, would it be catastrophic to power it up for a few minutes at a time with a heatsink but no compound on Q3 just to test it out?[/QUOTE
I would think you'd be safe to do that. Mine was completely dry originally. Seems like even dry there would be some heat transfer. I don't know for sure though.
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Ok...progress! Decided to take the plunge and hook it back up with the heatsink and no compound, just to test (I'll install the compound when it arrives and refrain from running it in the meantime). Voltages have changed somewhat:

Pin 2: -25 VDC (should be -31)
Pin 6: 25 VDC (should be 31)
Pin 10: -33 VDC (should be -41)
Pin 13: 13 VDC (spot on!)
Pin 14: 6 VDC (spot on!)
Pin 17: 29 VDC (should be 30)

So, I think this is good. They don't appear to be quite where they're supposed to be, but I'm happy to at least see pin 10 back in the negatives. Is there some kind of adjustment I need to do now given all the new components? I wonder if the filter cap that pin 2 is connected to might be the problem. Also not sure how much variation is acceptable here - I assume the 29V vs 30V on pin 17 is OK, but would 25V on a 31V pin be OK?

For those curious, the 100W bulb was too high. I couldn't even see the filament glowing when powered up, so I guess 60W is the sweet spot. I'll keep the 100W around for if and when I find something beefier to work on ;)
 
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Took me long enough, but I was just reminded that the DBT messes with voltages. Hooked it into mains (after verifying all is well with the DBT) and all pins check out! Looked at the speaker outs and they also look good now. Appears to me as if the problem is solved! Is there anything else that would make sense to test? I'll keep updating this thread with my rebuild progress.
 
In the service manual there is the bias adjustment, basically the current flowing across the output transistors when it is sitting there doing nothing. I believe it is 20 mV between the green wires going to each pair of output transistors, the actual pin numbers are in the SM. The trimmer on the amp board controls it.

When bias is much higher than spec you can have a unit running noticeably hot.
 
dly66 said:
In the service manual there is the bias adjustment, basically the current flowing across the output transistors when it is sitting there doing nothing. I believe it is 20 mV between the green wires going to each pair of output transistors, the actual pin numbers are in the SM. The trimmer on the amp board controls it.

When bias is much higher than spec you can have a unit running noticeably hot.
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Yep, I'm saving that to adjust after I recap the amp board. Still need to pick up a pair of dummy resistors too.
 
Ok, amp board is done and re-biased! Everything is working, except that the hiss/static from the headphone output that I've been trying to fix is still present. Haven't gotten the chance to test speakers yet, but the readings from the speaker terminals at least look good. Only board left is the preamp - I'm a bit scared of this one, since it looks hard to properly access. After that's the big filter caps, and then I'm done! Here goes!
 
Looks like someone has messed with my Tape 1 button:
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The same post that you can see broken is broken on the other side as well. The top of the pins also have some solder connections. Come to think of it, the Tape 1 input was kinda muddy...might this be the reason? Are these kinds of parts generally replaceable?
 
That broken pin looks like it may be factory. I've never seen it but it would take some effort and know how to know which pin to break. Are there any other photos of this board online to compare to?
 
Found this board on eBay, pins are not broken and there’s no solder connections up top.
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Doesn’t look like fromnowon’s has the solder connections either.
 
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