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Is this what a bad transformer looks like? (QSC CX12 amplifier content)

I had a 120v fan on the Adcom and I used 600 ohms which dropped the fan voltage to about 75v. I added a bypass switch to the amp as well so if you are rocking the house you can run it full speed.
 
Bradbrews said:
I had a 120v fan on the Adcom and I used 600 ohms which dropped the fan voltage to about 75v. I added a bypass switch to the amp as well so if you are rocking the house you can run it full speed.
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Good idea- would a PWM work here? I think I have one of those in a drawer somewhere...
 
Some of those power caps may have a bulged top. Side photos would be nice. :)

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tlite said:
Answered my own question- a PWM does work. Not sure if it's the best solution, but it works.
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Unnecessary complexity, IMO.

Should be a two stage fan circuit already. If you change to a lower speed/volume fan (or resistor, but I prefer the fan way because the fan is old anyway) that's good for normal duty, it should still kick up to a higher speed if/as necessary for higher demand.

With 400wpc @ 8 and 600wpc @ 4, it should be loafing along most of the time if being used in a typical home stereo situation.
 
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+1

The pro amps I use at home barely even get warm. And those are the convection cooled models. The ones that have fans always blow out cold air.
These things are meant to put out close to max power for hours at a time without self destructing. In anything from freezing to 90+ degree temps.
 
elitopus said:
+1

The pro amps I use at home barely even get warm. And those are the convection cooled models. The ones that have fans always blow out cold air.
These things are meant to put out close to max power for hours at a time without self destructing. In anything from freezing to 90+ degree temps.
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Think I could unplug the fan altogether? I could put a thermometer in there and check- what's a reasonable max temp to shoot for?
 
I am wondering why 7 of them are SMH and 1 is KMH. Did one have to be replaced for some reason?
 
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roger2 said:
I am wondering why 7 of them are SHM and 1 is KMH. Did one have to be replaced for some reason?
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Great question but No clue. Regal cinema owned it prior to me so I'll never find out. As discussed next time I get over there I'll try to pull another unit and see what it has.
 
tlite said:
Think I could unplug the fan altogether? I could put a thermometer in there and check- what's a reasonable max temp to shoot for?
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Personally, I would not. They are designed to have some air movement through them. The heat sinks are sized for forced air, not convection cooling.

Will it work without any fan at all? Yeah, I'm sure it would for some period of time.

In theory the built-in thermal sensing would shut it down if it gets close to the danger point. But, heat is the enemy of electronics so anything that causes it to run appreciably hotter than expected will only cause it to expire sooner than it otherwise would. OTOH, you paid nothing so you have no real out of pocket to lose if it goes tits up prematurely.

When I did the fans in my PLX series amps I was able to take the model number off the OEM fan and find the datasheet for them. In that series of fans were high, medium, and low speed/CFM fans. The OEM were the high speed/high CFM, I ordered the low speed/low CFM models. Direct drop in and now the fan/air noise from the stack of four amps is inaudible from more than a foot or two away.
 
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roger2 said:
I am wondering why 7 of them are SMH and 1 is KMH. Did one have to be replaced for some reason?
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Yeah, a repair all but certainly.

In every one of my QSCs, and I have several, all the capacitors in banks similar to that are of the same series.
 
Got it hooked up and snagged a 200 ohm resistor to slow the fan, and (almost) all is good.

I DeOxited the pots and switch, but I get no right channel when the amp is set to stereo. (The other modes are "Bridge" and "Parallel" and I get right channel on those.)

Front panel just shows green power lights like it should...

Any troubleshooting ideas?

EDIT: BAD CABLE. ALL IS WELL!! Many thanks, AK!
 
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Yeah, that it worked in parallel suggests something wrong right at the input jack of the amp, or cable, or source because selecting parallel mode simply connects the left and right inputs internally in parallel. You confirmed the cable.
 
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