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QSC Model 1400 - 9v DC at terminals

A

AyEss

Member
Hey everyone.

Bought a QSC Model 1400 off ebay, been sat in storage for years..
Powered it up with a dim bulb.. All perfect.. Starts up exactly as it should...

But i noticed that upon power up, Channel 1's CLIP light flashes once.. very quickly....
and there is 9v DC at channel 1 speaker terminals... But slowly drops to around 3v, once left idling...

I did a quick check of the T-03 transistors.. They all seam to be fine...
Also tried to swap in some brand new NE5532 OPAMP's.. I had them in my stock, and its a quick check...
No change...

Is there anything specific, or common, to look for on these amps?

cheers
 
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Update?!?!

checked all the diodes on the board.. All the resistors too.. All test perfect...

Removed and tested the driver transistors.. All great
Removed, tested and applied fresh thermal paste to the T-03 transistors.. All great...
Removed and tested bridge rectifiers.. All tested fine...

After installing everything, and cleaning the 8 pin socket for the OPAMP's..
Im now getting a slightly better reading on Channel 1 speaker terminals..

Upon cold start.. It will start with 1v on terminal... Then after a few seconds it will jump to 8-9v DC...
But if i leave it to warm up (still on 100w Dim bulb) (230v here in the UK), Channel 1 DC offset will slowly drop down, to around 58mv.... Which is great!!!!
But it takes soo darn long to drop!!! Literally 8-10 minutes of it being idle..
Meanwhile, Channel 2 always has 11mv DC at terminals.. even on cold power up...

But even after it has warmed up and the DC offset has dropped, I still have a red LED illuminated on the board.. Which according to QSC manual.. means its in protect...
It never turns off...
I have followed the manual and tested for 14-15v rail at a diode etc etc.. All tests show fine....
 
Another note:
After bein sat idling for a while.. the DC offset will drop right down to 58mv..... but if you continue to leave it idling.. It will slow beginto rise again...
115-120mv... and still going up
 
Recapped the entire amp board with Panasonic high grade caps.. No change...

If i power amp on dim bulb... I get a quick flicker of the Channel 1 clip light upon power up, dc offset at the terminals sits at mV's for a few seconds, then jumps up to 9v after 4-5 seconds...

When powered straight from wall... Channel 1 clip light stays permanently illuminated.... Same amount of DC offset at the terminals...

Hmmm
 
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