2. amps-preamps
  3. 133811-108496

Opinions re: debugging/repairing Cambridge Audio 540A amp stage

Hey! My old Cambridge Audio 540A has seen better days. It's been acting up recently. I'm interested in fixing it up myself if I can, but I'm looking for opinions on where to start.

Symptoms: speaker output on *any* channel (L/R, A and B) can drop instantly from the correct level to partial (including zero output). It does not happen consistently: on some audio streams, it seems more stable, but I have no way to reproduce reliably. The drop is instantaneous, not a slow shift. I can reset the audio levels if I switch input selector and back, until it happens again. If I do nothing, sometimes the audio will click back into place on its own.

This can happen on any input. Multimeter suggests that the voltage on the output drops when the audio drops; I don't suspect an issue with the speakers, but I don't have spares to test with. Headphone output is always perfect. My suspicion has been the amp stage in the 540A.

This is not a new unit, and so I popped the top off. My first suspicion was the big capacitors, because of age and the gunk they'd deposited on the board: https://i.imgur.com/u0Qnj8O.jpg  So I've cleaned those and replaced them. The problem persists, but I didn't have replacements to hand for the smaller capacitors.

I'm feeling my way around as I go; I have a copy of the service manual so I can decipher things, but I'm looking for good approaches to debugging these units to home in on the problem.

Note, obviously I can replace this unit easily. But if I can fix it, I'll feel happier, and I'm also happy to get my hands dirty. I'd appreciate pointers from folks on what to attack!
sodsto
Post removed 
mesch
3,481 posts
 
I own a 540A which i am using in a secondary system. I believe it was manufactured in 2004, I bought it used here on AG for $150 shipped to my door.
It is probably worth that today. 

Given the above, if something like what you are experiencing happens to this amp I would be inclined to open it up and look for obvious things however not invest to much time or expense trying to repair. Your amp could easily be replaced via the used integrated market at less expense than a repair and you could own a newer integrated. Just my thoughts.

Good luck which ever way your proceed.
 
sodsto OP
3 posts
 
Thanks for your responses!

Without doing anything significant today: if the gunk on the board was glue, it was no longer adhesive. It flaked away when I scraped it; only the solder held those old capacitors in place. Also, if the system's protection feature clips the audio, it never triggers the flashing light that should tell me it hit a failure mode. Also, the system doesn't appear to be super warm; one of the heatsinks accumulates a good amount of heat, but that's where it should go anyway. It's not warm enough that I'm concerned. I don't suspect the volume control since audio via the headphone jack is always perfect.

And yes, I could pick up even a new low-end CA amp to replace this and be quite happy.

But, this amp has been so good that if I could nail down (easily) what's wrong, it'd be great to fix it. I'm more used to electronics boards with chips, though; CA's wiring is a bit of a riot. And since some of the voltages via the amp stage are nontrivial, I'm definitely not poking anything I'm not sure about.
teo_audio
2,197 posts
 
Relays
sodsto OP
3 posts
 
One word might nail it?

From that post, I happened to land on https://www.dinkum.nl/music_and_sound/cambridge_repair/
More to discover