EV 7200 power amp 1 channel not working

[treatmint]

I have a EV 7200 power amp. I'm not the most experienced with repairing electronics but I wanted to try and troubleshoot this issue. I noticed that the channel in question began to get weaker in terms of volume output gradually over the course of several band rehearsal sessions. It got weaker 2 or 3 times before going completely out. Anyone that could advise me on where/how to start figuring out what might be wrong with this one channel would be greatly appreciated. Thanks in advance.

[J M Fahey]

Start by asking them the schematic and posting it here.
Otherwise we are in the dark.
Good luck.

[treatmint]

The manual for this amp is listed below.
What other information do you need?

[Jazz P Bass]

Man, there are nice tidbits of information in the manual (ie: wattage loss versus cable length)
Anyway.
What skills do you have as far as troubleshooting safety & procedures?
This is a solid state amp. The output section runs in class B. Until something goes wrong
What equipment do you have?
A decent tech will have, at the minimum:
A good DVM.
A good 25W solder station.
A good solder sucker.
A signal generator.
A scope.
An ammeter.
I am not trying to be snide.
You have every chance of ruining the amp without proper caution, procedure & equipment.

[treatmint]

Jazz P-

I don't think you're being 'snide'...I honestly appreciate any and all feedback I can get.
As I said, I don't have much experience in the way of repairing electronics...I'm more mechanically inclined, but I have a friend who is really well versed in this sort of thing. So I was trying to find a starting off point for when I can get with him to start troubleshooting. He has all the equipment you mentioned and then some. Again, thanks for the response. Like I said, it seemed like the power just faded out on that one channel and then went completely dead. I wasn't sure if someone here would know (based on those symptoms) what might cause something like that.

[jrfrond]

The "weaker and weaker" thing sounds like an intermittent that finally opened, perhaps even a speaker relay.

[Jazz P Bass]

Quote"I wasn't sure if someone here would know (based on those symptoms) what might cause something like that. "
This is why I refuse to give estimates.
It could literally be anything.
I would not want to "walk" your friend through "how to check an amp" but there are a few basic things.
That said, the signal chain through an amp can be divided into blocks.
The final outcome, "the speakers make sound" involves all of these blocks.
And worse yet, most of the blocks are a long series chain from the input to the output.
ANY block failing can cause a compromised output.
I would suggest first, a static check of the amp looking for output transistors or power rails shorted.
Compare readings to the working channel
If nothing comes up here I would turn on the amp & check the power rails & output transistor voltages.
If that is good, then you send a signal through the amp & verify where it is failing.
Which "block".

[J M Fahey]

Adding to what is posted above, I am also somewhat puzzled by the "fading along a certain time (days?)" bit.
It's not very usual, specially in a power amp.
You *might* (take this with a huge grain of salt) even not have a dead amp at all, simply one where signal gets lost along the way, as suggested.
You are not mentioning blown fuses, smoke, charring, triggered protection LEDs, etc. so let's hope for the best.
Start by checking DC voltage at the junction of R31 to R40, which is also one end of L01 and same parts (+100) if on the other channel.
Post results.
Identify the non working channel so from now on we refer to correct number parts.
Try to have your friend talk straight to us here (using your account if you wish); otherwise meanings get lost in translation.
Good luck.