Ampeg VH140C

[Poser]

Hello and thank you for adding me to the forum, I'm glad to be apart of this place.

I recently got an Ampeg VH140C and the chorus section is having issues. It worked fine without the selector pedal for a while, however it soon started to cut in and out. Thumping the amp helped for a moment but would stop working again. I'm starting the repairs with a simple pot and jack cleaning, then will check the solder joints. I've played through many amps and this model, even with its major flaws, is an absolute favorite.

So, what's the deal with the ss/vh ampeg, why are they so fragile? How do I keep this amp going?
 

[pdf64]

It's in its 3rd or even 4th decade of use / abuse, probably single sided, non through hole plated pcb?
Lots of failing solder joints are to be expected.
The symptoms match up with that.
Ideally inspect the board joints first, using visual magnification and dyrong lighting, to try to identify the culprit/s. Those for the sockets and pots are typically under the most stress.
Then reflow every solder joint in the thing, remove old solder first, especially if there's an excess.

[Tassieviking]

I would keep bashing that amp as long as you can afford to replace the reverb tank cause it is bound to get damaged with that sort of abuse.

You most likely have a bad solder joint, dirty contact or even a cracked track on the PCB (which is not that uncommon with amps that have been abused)

Schematic:

[Poser]

I would keep bashing that amp as long as you can afford to replace the reverb tank cause it is bound to get damaged with that sort of abuse.

You most likely have a bad solder joint, dirty contact or even a cracked track on the PCB (which is not that uncommon with amps that have been abused)

Schematic:

Thanks for the schematic, that is going to help out a lot. Yeah the amp has definitely been gigged. it's the last one I'm getting for a long time, honestly I'm considering to ship the pcbs out to be cloned.

[g1]

The chorus footswitch jack may be beyond cleaning.  If you don't have a footswitch to try, put a shorting plug in the footswitch jack. Or solder a jumper across the jack's tip and sleeve solder pads at the board.
Otherwise I'm in agreement with the others about the solder joints.

[Poser]

Here's an update after disassembling the amp:

Found a decent number of cold solder joints across the chorus/reverb section, each board has an excess or anemic amount of soldier on a lot of joints. Surprisingly enough, the thermal paste used in this amp is still mailable. As pdf64 suggested, a reflow of every joint should be done. New thermal paste will be applied. If possible I'd like to scan and upload these pcb boards. I've reached out to a few pcb cloning manufacturers to see if I can get these boards replicated.

I can see why these amps go out all the time, they seemed to have been rushed together during production and there's no ventilation in this amp. Still, they are pretty badass and worth the headache imo. 

[Tassieviking]

It would be better if you make up new PCB's then getting the old layouts re-made.
Just get the measurements between pots and switches and jacks etc. and draw it all up in something like KiCad and make brand new layouts.
Usually the old PCB's have no ground-plane and are poorly designed so the components don't fit that well on the board.
Some old layouts make the PCB really large and will cost a lot of money to get reproduced, if you do it well you might get away with a PCB that is far less then half the size of the original.
Do you have any pictures you can share ??

[J M Fahey]

In the old days PCBs were fully hand drawn.

Problem being than these designs are very interactive: you first design a draft board, then improve improve improve, push this component there, bring that one closer, separate sensitive tracks, reroute grounds for lowwer hum or interference, the works, as many times as needed.

When boards were hand drawn, you improved them a little and leave it there, because it´s a lot of work.

With software design, it is easy peasy to reroute and redraw everything on screen.

Here board will not be smaller (maybe somewhat narrower) because pots and jacks need to fit on front panel, but you can improve layout and grounding big time.

And order many for low cost.

[Poser]

Update:

I've flowed almost every joint on each board, some were so small that I opted to leave alone for fear of overflowing the solder and joining something that shouldn't be joined. Replaced the thermal grease and cleaned each pot/input with d100 deoxit. The chorus works without it cutting out, but now it only works in channel a and works in an opposite fashion. Instead of the depth of the chorus climbing from 0 - 10 it now works from 10 being nothing, 3-4 being the most intense and 1 being more subtle. With channel b, the stereo kicks in but has no chorus or reverb. I need to go back in and see what I did wrong or missed. I'll post pictures after I find another image hosting site, tumblr is giving me issues.

[Poser]

***as soon as I got home I tested out the chorus and reverb section, I didn't realize the chorus rate only really kicks in when you strum. Everything seems to be working fine.