[ctviggen]

I sent my QSC 3402 amp to get fixed.  They supposedly performed work on it (and definitely changed the fan from the nice quiet one I put in to one that sounds like a jet engine), but the one broken channel is still broken.  This channel partially works.  For instance, if I put a sub and IC on channel 2 then play a test song, the sub is rocking.  If I put the same sub and its interconnect on channel 1 and play the same song, the sub has some movement but not much.  Thus, channel 1 is operating but at a reduced capacity.

QSC is nice enough to put schematics online:

http://www.qscaudio.com/support/technical_support/schems1.htm

I've already sent it to them once and paid (it's out of warranty) to have it fixed and they did not fix it.  So, I'm thinking of fixing it myself.  

My questions are as follows.  When I go to debug this amp, I'd like to compare channels, as I know one channel works.  This way, I go step by step through each channel until I hit a device that no longer appears to work.  Is this a suitable debugging scheme?  Do I need an input (of say a 300 Hz test tone from my CDP)?  What about a fake output?  Or can I just test them unloaded?

I fixed my Creek integrated amp, but that was a different animal than the QSC.  The Creek had 24 volt rails; the QSC has 400 volt rails!  Yikes!

Thanks for any answers.

[ctviggen]

I should note that I wanted to purchase two Ref 9s and just leave the QSC for debugging down the road, but alas I cannot afford the two Ref 9s at this time.  My two VMPS Largers have been sitting and taking up space and I'd like to finally use them, even if I only use them for movies (my room is so large that my SVS doesn't have the oomph required).

[_scotty_]

ctviggen,how big is your SVS sub.
Scotty

[ctviggen]

Well, I have two VMPS largers.  I currently have them on stands and the combination of the stands and the Largers mean a huge sub/stand combination!  

QSC not only have the schematics for free, but also will send a tech support DVD to me, for FREE.  Amazing!  Perhaps I should take back my "don't buy QSC" post.  I'm going to use the support DVD and schematics to determine what's wrong.  I think I'm going to use my CDP, which can also be a preamp, and put in a low level, single tone signal.  Then, I'll connect some small speakers to the QSC.  This way, I can test the amp under load.

[ctviggen]

I'm sorry -- I answered the wrong question.  I have an older model of this:

http://www.svsound.com/products-sub-cyl-plpow2.cfm

I did upgrade the driver, though.  In my room, it's anemic for movies.