Diagnose the problem with my amp

[blue fury 3]

I have an old school memphis Belle 6-ch amp. Here is what I know for sure:

-Channels 1-4 work fine. (4x75@4)

-Channels 5 and 6 have possible the same problem, but 6 has it worse. (2x150@4 playing 80-250hz)

-Channel 5 works maybe half the time at start up

-Channel 6 never works on start up.

-Power/ground/remote is secure and is 4awg.

-Both speakers are connected properly.

-Both speakers have power from the amp (I know this for a fact)

-Neither speaker is blown, both have good coils and leads.

-The RCAs are good and both send signal to the amp (again, I know this)

-If I play a tone within range of the band pass and gradually turn up the volume to about 80% up to the volume I set my gains at, channel 5 will play a bit of static like it has a loose connection then play consistently at full output (with respect to the HU volume level)

-If I play the same tone at the volume that the gains were set at or maybe a notch higher, channel 6 will emit very short ticks of static. I want to turn it up higher to 'bring it to life' like the 5th channel, but I don't want to cause any more problems.

Another note, I noticed that after I 'wake up' the 5th channel, it may go out again. It does not cut out, it fades out. I can repeat the process by playing the tone to wake it up again. I don't do it very often to try and avoid further problems.

I've never pushed this amp hard or anything, I've treated it with a lot of care. It's got to be something in the amp but I've never dealt with amp problems before. It seems to me that by turning it up, the amp has to work harder with heat as a byproduct. This heat inadvertently softens a cold solder joint enough to enlarge the solder to establish a better connection. This could work for the 6th channel but the gap in the connection is too big for the amount of expansion caused from the heat of normal use. But that idea is probably wrong.

What could it be?

Edited January 28, 2010 by blue fury

[KU40 173]

I had a similar problem in an amp that would come to life only when I turned the volume up quite a ways, then would later fade out or cut out sometime. The amp is toast. I believe when I opened up the case a couple of the mosfets were a little burnt. I tried replacing those but it didn't fix it, so there must have been something else wrong but I wasnt' skilled enough in amp repair to diagnose it. If channels 1-4 work, I'd just use those channels and then get another amp for the remaining speakers you need to power, unless you want to send it in for a refurbishing. If it's not under warranty, however, open it up and see if you see anything wrong.

[blue fury 3]

So I got both channels to work for some time today. I went to an electronics repair shop recommended by a local shop to see what they could do. Idk if I'll actually take it there because it was reeeeeeeeaaaaalllllllllllllllllllllllllly messy, all kinds of shit piled up everywhere, a dog inside the shop and the owner wasn't even around. The wife that barely spoke English that had only like half her teeth told me he went for a walk.

yuuuuuuuuck