KA-9100 Switch Pop

[tinkerer]

Opened this can of worms back up after setting it aside for awhile. I had become quite frustrated with the whole thing. I'm in a somewhat better frame of mind now after the break.

Checked all my capacitor orientations and they are good.

Got out my magnifying glass and started looking at wires, solder joints, traces, etc. Found a bridged solder joint associated with the high filter switch, so that issue should be resolved. I'll know when I put it back together.

Still have the pop in the loudness and monitor switches to deal with. I thought I'd replace transistors on the tone boards since I've got it opened up again. But I've seen different opinions on this. Some say the transistors are pretty hardy and to leave them alone. Any thoughts on replacing the transistors on both the tone boards?

 

[50nstillhifi]

Opened this can of worms back up after setting it aside for awhile. I had become quite frustrated with the whole thing. I'm in a somewhat better frame of mind now after the break.

Checked all my capacitor orientations and they are good.

Got out my magnifying glass and started looking at wires, solder joints, traces, etc. Found a bridged solder joint associated with the high filter switch, so that issue should be resolved. I'll know when I put it back together.

Still have the pop in the loudness and monitor switches to deal with. I thought I'd replace transistors on the tone boards since I've got it opened up again. But I've seen different opinions on this. Some say the transistors are pretty hardy and to leave them alone. Any thoughts on replacing the transistors on both the tone boards?

I would leave them... unless there is a direct effect they would have on eliminating the popping you are concerned with.

I don't believe them to be a contributing factor.

 

[tinkerer]

50nstilhifi not sure what else to try.

I have removed the Loudness switch, disassembled, clean/lubed, and it had no effect on the pop. I have removed the Volume/Balance control twice, clean/lube , and it has no effect on the pop. All the controls have been cleaned at least twice. I cannot guarantee all the switches are clean, but I'm not going to remove any more switches, too big a job and too high a chance of lifting traces with the bent over lugs etc. (I need a vacuum solder sucker )

The power supply board has been recapped, no transistors were replaced. The relay contacts looked good from what I could see, so I did not mess with them. The power supply-protection-relay seem to be working normally.

I may only replace transistors on the X11-1410-00-A/4 tone control board.
From reading other posts it appears the following are popular replacements:
Q5,6: 2SA850........KSA1013
Q7,8,9,10: 2SA847........KSA992
Q11,12,13,14: 2SA850........KSA992

Still considering....but probably will.....if the transistor subs are good subs.....I'm willing to give it a try.

 

[50nstillhifi]

Hmmmm.....

Exactly when do you hear this "pop"?

Is it before or after the speaker relay switch activates?

 

[tinkerer]

The pop is in the Loudness switch when returned to center from up or down, and in the Tape Monitor switch when activated to A or B. Right meter will jump when Volume is returned full counter-clockwise to no volume.
This is when the unit is powered up and playing.

 

[tinkerer]

Thanks rjsalvi. Traveling the last few days.

Pop is Right Channel ONLY last time I had it assembled. Replaced transistors on the X11-1410-00-A/4 Tone Board and have not reassembled yet to check the condition. Going to give the controls another round of Deoxit while they're accessible.
I have desoldered and cleaned the Vol/Bal pot twice.

J9-J9-J12-J15 Grounds are good. Checking others for broken wires etc.

Do not know if the pop gets louder with volume, will have to check that when I reassemble.

 

[tinkerer]

Reassembled. Still go the pop.

Pop does get louder with volume.

I'm going to play it on real speakers, test sound on phono, aux, etc and see if it's an issue I can live with.

Pretty weary of this amp. Disappointed I can find the problem.

 

[tinkerer]

Hooked it up to a real system (vs small test speakers) and it played fine.

Except Right Channel phono was gone, but so was the pop thru the switches.

Started tracing the sound thru the X11-1410-00-D4 Control Board (Phono EQ). When I probed a leg on Q32 - 2SC1904 sound came thru the right channel. Hot dang....cracked solder joint. Got really lucky because that's right up top and easy to resolder without having to tear everything down again. Resoldered and playing fine without pop in controls. As much as I had looked at these boards under a magnifying glass I still missed that bad solder joint. I can only assume that was causing the pop also.

Gonna let it play for awhile, burn in the new capacitors and transistors, and recheck the Center Voltage - DC Offset on the amps. If everything checks out I'll call it done for now. Down the road I'm sure the amps could use a rebuild.

Thanks everyone for all the help.

 

[gort69]

Don't remember an accompanying pop from any switches, but it's been awhile. Good find.

http://www.audiokarma.org/forums/in...50-x11-1410-00-d-4-eq-amp-board-issue.759396/

Here's the picture in case you can't see it in the linked thread.

 

[tinkerer]

Yep that looks very similar to what I found.
I'm not tech savvy enough to know if the bad solder joint caused the pop in the switches. I just know it's gone.

Cheers

 

[50nstillhifi]

FANTASTIC!!

Now you can enjoy that unrelenting power the 9100 is capable of providing... and across the audio spectrum.

On another note, this exercise stresses the persistent and involved testing of these older model boards. They have weathered a lot of heating and cooling, this in itself leading to future issues.

I really like how this became a collaborative brainstorm involving posters having done the work and not relenting to failure.

Good job! For me... this is what hallmarks the enjoyment of vintage equipment.. and keeping that ever diminishing 50s to 80s.. "solid state" heartbeat going TO THE BEER FRIDGE!!

 

[tinkerer]

Thank You

Thanks to all again for the help.