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SX 950 power board issues, and issues down stream

Spoke too soon. It is actually running and doing well. However randomly I get a small pop in the left channel only, still not seeing DC current but I may miss when it comes through. Also at the same time I get all of the orange lights on the front display flashing brighter a couple of times then go back to normal.

Now what is strange, if I out it on an unused input instead of fm tuner it seems to happen faster. Like it has a charge that is building if it is not used in the amplifier circuit.

I may still just keep changing caps and transistors as I am pretty sure I have a failing cap that is still sending stray current every once in a while. Any opinions?

Thanks Troy.
 
petehall347 said:
pops are generally transistors .
Click to expand...
Well, good thing I planned on replacing them all one board at a time. I just tested the phono 1 and 2 inputs and sounds good. Lots more work to do. I'll put it up for now and work on it more another day. Lots of removal and resoldering.

Thanks. Troy.
 
The lamp circuit is designed with a minimum load required for brightness stability, if you have a bulb failing open or an intermittent switch contact momentarily decreasing the load, the lamp circuit voltage will rise, brightening the other lamps. Or a failure of Q9, Q10 or C14 in the capacitance amplifier/filter circuit on the AWR-101 power supply pcb. Rebuild the AWR-101 first, caps and transistors. Switching to a different input selects different lamps also. That may be the source of your pop, since it is concurrent with the lamp flicker.
Recap and replace transistors and VRs on the power amp next. Center the dc offset VRs (1 & 2) and turn the bias VRs (3 & 4) to 0Ω when installed. Manufacturers may preset them to midrange, which could be too high for a safe bias setting at first power up.
Deoxit all the switches, Faderlube the pots.

Suggestion for Q10, 512-2N5551TF, Mouser: https://audiokarma.org/forums/index...ore-was-in-a-fire.908404/page-2#post-13653378
 
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merlynski said:
The lamp circuit is designed with a minimum load required for brightness stability, if you have a bulb failing open or an intermittent switch contact momentarily decreasing the load, the lamp circuit voltage will rise, brightening the other lamps. Or a failure of Q9, Q10 or C14 in the capacitance amplifier/filter circuit on the AWR-101 power supply pcb. Rebuild the AWR-101 first, caps and transistors. Switching to a different input selects different lamps also. That may be the source of your pop, since it is concurrent with the lamp flicker.
Recap and replace transistors and VRs on the power amp next. Center the dc offset VRs (1 & 2) and turn the bias VRs (3 & 4) to 0Ω when installed. Manufacturers may preset them to midrange, which could be too high for a safe bias setting at first power up.
Deoxit all the switches, Faderlube the pots.

Suggestion for Q10, 512-2N5551TF, Mouser: https://audiokarma.org/forums/index...ore-was-in-a-fire.908404/page-2#post-13653378
Click to expand...
I will start by finishing the recap and new transistors for the power board. I check the bulbs. I am not getting any popping while changing inputs. I'll see where we go from here. I will sit down with my list of caps and see what I should change to
 
Rathwine said:
I will start by finishing the recap and new transistors for the power board. I check the bulbs. I am not getting any popping while changing inputs. I'll see where we go from here. I will sit down with my list of caps and see what I should change to
Click to expand...
I may have it reversed, it may be the pop is drawing a large enough current from the transformer to make the lamps flicker. Either way, we can figure it out and fix it. Does the pop come from one channel or both?
 
merlynski said:
I may have it reversed, it may be the pop is drawing a large enough current from the transformer to make the lamps flicker. Either way, we can figure it out and fix it. Does the pop come from one channel or both?
Click to expand...
Left channel only. Seems to come faster when. I speakers are on or when no source is playing. When I have speakers on and play a source the pop comes less often and is not as strong. Lights still dim and return. When I get home I can check some voltages and see if something is out of whack.
 
Rathwine said:
Left channel only. Seems to come faster when. I speakers are on or when no source is playing. When I have speakers on and play a source the pop comes less often and is not as strong. Lights still dim and return. When I get home I can check some voltages and see if something is out of whack.
Click to expand...

Good info, lessens the likelihood it is the lighting circuit causing it.
It can wait for your schedule, of course.
Does the position of the volume control vary the loudness of the pop?
 
merlynski said:
Good info, lessens the likelihood it is the lighting circuit causing it.
It can wait for your schedule, of course.
Does the position of the volume control vary the loudness of the pop?
Click to expand...
Ok notes from trials. Seems to be more than one problem.

Pop in left speaker does not seem tied to anything that I can find. I am on speakers b now and got a good pop while playing music from the radio. Also got a pop while playing aux input. Volume does not seem to affect pop volume.

Flashing of lights has nothing to do with the pop. They are independent. Flashing lights is less noticeable as more lights come on. If I turn on 2 sets of speakers that are not hooked up, little brightness with flashing. Also does not flash as often.

If I use 1 set of speakers that do not have speakers hooked up, lights get very bright and flash a lot. This happens on all but phono 2 input.

If I turn on speakers that play and radio input, less flashing but it happens and I get static or scratchy noise from right channel. It is at a low volume so if music is stronger you only seem to hear the music.

I have a DC meter hooked up to left channel, trying to catch a pop and measure a DC spike.

There is no pattern showing with DC and the flashing lights and scratchy sound on right channel.

DC voltage regardless of input sound is between -.03vdc to -.010vdc. this is on left channel.

DC voltage on right channel is running +.020 to +.025.

Next we get small noise with the input out on anything except phono 2. Phono 2 is by far the loudest noise and most flashing lights.

Over 30 minutes with music playing and lots of switch changing only got 3 pops from left channel. Lots of static on right.

Also changing from phono 2 to anything else and back causes flashing and static, and a little of a pop. Likely a dirty switch for phono 2.

Also just noticed that am radio does not work. That is the least of my concern just noting it. All other inputs work.

A lot to digest and I think likely several problems. I am happy to focus on whichever is the best one to work on.
Thanks a ton.
Troy.
 
After playing at low volume through 8 ohm speakers, jbl 4408's, level 1.5, protection mode clicked in. Could not get it to reset. Tried turning off speakers changing filter settings, power off and then on after 5 seconds

Ended up disconnecting speakers, turned it back on, and when I turned off speakers b, protection mode turned off. I am thinking maybe heat with questionable parts. Got too hot and tripped protection when it got too out of spec .

It is off now and no speakers hooked up.

No smell, no smoke, does not even smell hot.
 
when its in protect get the voltages on the protect circuit all the pins .
i am suspecting Q1 Q2 protect circuit .
i also suspect pin 12 7.5V AC this is to detect its switched on .
 
If the volume control has no effect on the pop, neither will input selection, as that is all before the volume control. The volume control is just ahead of the Pre-out Power-in jacks. Pull the jumpers between Pre-out and Power-in, turn it on and see if a pop occurs.
This kind of pop usually comes from the voltage amp section of the power amp.
The lights brightening and dimming is a different problem.
 
yes the differential pair definitely suspect .but with the lights flashing issue i wondered if its a power supply issue . maybe corroded fuse holders .
 
The similar lamp issue has been resolved in another SX-950 and SX-850 by replacing Q9 (2SD313) with a 512-KSD526Y and Q10 (2SC869) with a 512-2N5551TF on the Power Supply pcb,AWR-101 (Mouser part numbers). A 0.1µf cap from emitter of Q9 to ground was suggest as a useful addition to reduce chances of oscillation in the circuit.
 
petehall347 said:
yes the differential pair definitely suspect .but with the lights flashing issue i wondered if its a power supply issue . maybe corroded fuse holders .
Click to expand...
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?
 
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?
Click to expand...
yes they will still work
its best to match the transistors . but will likely dial in ok if not closely matched
 
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