Ampeg ss140c no sound

[boog]

I haven't dug into this thing much yet, it does turn on, I can hear static in the speaker (especially moving the chorus controls) channel controls don't seem to be making any difference, I'm not sure if it is even switching to channel a yet (no led) also no chorus led, voltages seem to be correct going to the power amp board and chorus board.
Problems I've found so far: r61 and r62 on the chorus board get very hot, I'm suspecting ic10 (79m15) -15 voltage regulator, as the readings on d9 are not near -15, all of the diodes in that area test good, and it looks like someone has put in 2 electrolytics in that area as well.

[boog]

does anyone have a source for these oddball potentiometers in this thing? my usuals are out of stock or don't carry anything close.

[Enzo]

Looks like a stock SLM pot to me, and that is a normal looking part number for them. Would also be used in Crate amps, if that helps your search.

[boog]

I haven't had any luck finding them in stock anywhere, I figured some crate parts would be the same, the ones under slm anyway.

[Enzo]

They are the same, SLM didn't make special Ampeg parts like pots.

I sold all my SLM pots as a bloc a couple years ago.

[boog]

I'll have to keep an eye out for a parts amp or something, I'm not having any luck finding them in stock anywhere, it's not mine or I'd replace it with a common pot like a cts mounted to the chassis, I'm sure the one in the amp works, just the threaded part has been broken off.

[The Dude]

Have you tried contacting Loud directly?

https://loudaudio.com/contact/

[boog]

Yes, the screenshot above is from their site, they were out of stock.
The parts should be here tomorrow so we'll see what works and what doesn't and go from there, the marshall pc mount pots look pretty similar, I'll leave the decision up to the owner.

[J M Fahey]

From what I see that one is a reguklar 16mm pot, BUT with and unthreaded neck extension so it sits some 8 or 10 mm further away from front panel, which is usually done so a few tracks can be tracd in that space.

Pot pads almost against PCB edge complicate layout A LOT. (don´t ask how I know)

If it´s one or two you can use a regular 16mm pot, bolt it with its own nut against front panel, bend legs backwards so they do NOT get into their holes (which will be misaligned by 8-10 mm) and add short copper wires for electrical connection.

You will lose mechanical connection but one or two such pots won´t significantly weaken PCB support.

[boog]

I agree, that is going to be my suggestion to the owner, and would have already done if it was mine, the regulator should be here later today, after I see what's working and what isn't we'll go from there, I'm sure the power section is good, hopefully the rest of the preamp is good to go.

[boog]

new reg installed, but there was still little resistance between the -15 output and ground, I found 4558 ic4 cracked, so I lifted jw13 and jw15? (hard to read the schematic) to see if that got rid of the low resistance at the regulator, it didn't, so next I pulled ic9 (maybe) another 4558 and found it was shorted too, so I stopped there and ordered 25 new ones, now more waiting for parts.

[boog]

new 4558 in at ic9 and ic6, 15v and -15 are correct now, it has channel switching and chorus, which it didn't to begin with, r61 and r62 are still getting hot, still no sound other than a hum when the speaker is on the chorus outs, dry outs are silent, I tried jumping the effects loop and pre out power amp in, and still nothing other than the hum going away when power amp in is used, so something is still wrong in the preamp, unfortunately I don't have a scope at the moment

[The Dude]

If you don't have a scope, use a test tone and your meter set to AC volts.

[boog]

I'm trying to track down what is causing r61 and r62 to heat up, I'm afraid to keep it on too long until I find the cause

[The Dude]

I don't see a schematic posted, but are there zener diodes after the regulators? If so, you could have a bad zener or 2.

Edit: Here we go.

https://ampeg.com/support/files/Sche...rts%20List.pdf