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SX 950 power board issues, and issues down stream

merlynski said:
Good on you for the dbt use!

I was expecting to see an exploded capacitor, caused by a large current leak or overload. That looks like a leaky seal oozed some electrolyte. Good call to replace it, but it relieves me a bit to see something small.


What does R19 measure? If it is 150Ω replace Q6 and the caps. What voltage do you have on AWR-101 pin 15 now?
Click to expand...
Pin 15 is now -16.1v with DBT.
 
Well so far so good. I am still going to replace the cap c18 on the eq board.

There is something wrong with the tone amp board as if I click the tone control the safety relay clicks off.

I am going to test on the tone amp board next.
 
merlynski said:
Does the protection relay stay dropped, or click back on when switching tone switch?
Click to expand...
Stays dropped. No sound in headphones and never clicks back. If I turn off the tone amp board sound comes back, relay clicks back. Something there is a hard short or something like that.
 
That sounds like a short to a power supply. Don't leave it on.
Pull the Pre-out Power-in jumpers and see if it still clicks.
 
merlynski said:
That sounds like a short to a power supply. Don't leave it on.
Pull the Pre-out Power-in jumpers and see if it still clicks.
Click to expand...
Ok. I didn't. I turned it off. I opened the time amp board but nothing looks burned or blown. I'm going to button that back up and pull the pre-out jumpers. Just a sec.
 
Ok pulled pre-amp jumpers, powered on with DBT again, wait for relay to click on, turn on tone board and no relay click. Turn off tone board and no click. With preamp out it doesn't short out.
 
OK, that is a good bit of information. Do you have access to the Tone Amp board?
If not measure dc volts at the pre-out jacks with the tone switch on and off, left and right.
Should not have dc present in either position on either side.
 
merlynski said:
OK, that is a good bit of information. Do you have access to the Tone Amp board?
If not measure dc volts at the pre-out jacks with the tone switch on and off, left and right.
Should not have dc present in either position on either side.
Click to expand...
On DBT
Tone amp off
L .016vDC
R .015vDC

Tone amp on
L 16.6 VDC (wow)
R 0 VDC

So there is a short to power somewhere.
 
Check C23, is it backwards? (on the Tone Amp pcb AWG-039)
Check the traces, as the silkscreen may be ambiguous with the + kind of in the middle, but the plus end of the cap should be towards the end of the board, not the middle.
 
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merlynski said:
Check C23, is it backwards? (on the Tone Amp pcb AWG-039)
Check the traces, as the silkscreen may be ambiguous with the + kind of in the middle, but the plus end of the cap should be towards the end of the board, not the middle.
Click to expand...
Looks right to me. The positive is to the outside of the board which is what the schematic shows. 15910565852489049367244727164191.jpg
 
Remove it, tantalum caps are notorious for failing shorted, then power up and see if the dc is gone. Test it while it is out. 2.2µF polarized caps are prime candidates for replacement with film caps. Do you have any 2.2µF caps of any sort?
 
merlynski said:
Remove it, tantalum caps are notorious for failing shorted, then power up and see if the dc is gone. Test it while it is out. 2.2µF polarized caps are prime candidates for replacement with film caps. Do you have any 2.2µF caps of any sort?
Click to expand...
I have replacements for that one. I ordered the 647-ukl1h2r2kddana from nichicon. Aluminum electrolytic cap. It is what was suggested on the board.
 
Ok everyone. I think that has worked. I got off work today, pulled the tone amp board. Removed c-23. Tested the cap. Unrecognized my my ic tester. Checked with a multi meter. Showed 1500 ohms resistance from either direction and held steady. No charging so not working as a cap.

I used DBT and tested power at the preamp out with tone board enabled. No voltage. (.001v dc). Took off DBT and tried again on line voltage. No voltage DC again. I out pre amp out/in jumpers and tested with DBT. No voltage. Line voltage, no voltage. Put in headphones, sounds good, no popping, sound in both channels. Tone controls all working. I am now going to check DC offset on output to make sure it is safe for speakers, and see what it sounds like.

This thing has an amazing tuner. Pulling in stereo stations from across Jax with no antenna. I am impressed.

Let me know if I have missed anything I need to test. I want to clean all switches again, and run this thing a bit before I tackle recapping all of the rest. I want to do that in stages. Power amp looks tough to access to change these out. All of the rest seems pretty easy to reach.

Again, thanks for the help and all of your knowledge.

Troy
 
One of the other techs on AK calls those 'capsistors' when they do that. Glad it is working for you :biggrin:.
The input caps C1 & C3, and the dc offset circuit smoothing cap, C5, on the power amp pcb AWH-050 had reverse polarity dc current through them to pass dc through the power amp on that channel to cause the relay to drop. They may have been damaged and should be replaced. If you are going to recap the power amp anyway I would do that board first.

Consider replacing signal path electrolytics, under 4.7µF, with film caps. Usually lower leakage and lower noise, and longer life.
Replace all those tantalum (blue drop) caps, regardless.
Enjoy that fine Receiver!
 
merlynski said:
One of the other techs on AK calls those 'capsistors' when they do that. Glad it is working for you :biggrin:.
The input caps C1 & C3, and the dc offset circuit smoothing cap, C5, on the power amp pcb AWH-050 had reverse polarity dc current through them to pass dc through the power amp on that channel to cause the relay to drop. They may have been damaged and should be replaced. If you are going to recap the power amp anyway I would do that board first.

Consider replacing signal path electrolytics, under 4.7µF, with film caps. Usually lower leakage and lower noise, and longer life.
Replace all those tantalum (blue drop) caps, regardless.
Enjoy that fine Receiver!
Click to expand...
Thanks. Yeah I am planning on replacing c1-6 and c-11&12 on power amp board.
Tone amp board c13-16, 19-26, 29 and 30.
Honestly when I had to spend for shipping from two vendors I just bought enough to recap all of the known failing caps and transistors. I even got new offsets and bias pots also.

Only thing I did differently is I only got .22uf and 1uf in film. The rest are low leakage aluminum electrolytic caps. I followed the parts list I found here for a full recap.

I have to go back and replace C-18 for the eq board so if I should change others to film it will not cost much. I think with shipping I have 80.00 invested in parts. I already had the tools and solder. Let me know about which other caps should be film instead and I will get them.

Thanks again.
Troy
 
Rathwine said:
Thanks. Yeah I am planning on replacing c1-6 and c-11&12 on power amp board.
Tone amp board c13-16, 19-26, 29 and 30.
Honestly when I had to spend for shipping from two vendors I just bought enough to recap all of the known failing caps and transistors. I even got new offsets and bias pots also.

Only thing I did differently is I only got .22uf and 1uf in film. The rest are low leakage aluminum electrolytic caps. I followed the parts list I found here for a full recap.

I have to go back and replace C-18 for the eq board so if I should change others to film it will not cost much. I think with shipping I have 80.00 invested in parts. I already had the tools and solder. Let me know about which other caps should be film instead and I will get them.

Thanks again.
Troy
Click to expand...
I ended up with about $300.00 in parts for my SX-1050 I am rebuilding, but that includes 2 new main filter caps ($28ea) and 8 output transistors ($7 ea), plus I bought 100 quantity lots of the most useful small signal TO-92 and TO126 transistors.
I will look for more signal path film cap suggestions.
 
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