Crown X4000

[pnut5150]

Hello all, I need help on a Crown X4000 power amp. It actually kicked the breaker in my home breaker box upon powering it on. I found two resistors on the power supply board that are blown out. They are metal film resistors. There is also a small rectangular piece in front of each resistor that has been hot. I assume they are some kind of capacitor? I have no schematics, can't find them online, nor will Crown give me schematics or any kind of information about the bad parts. I can provide board location numbers of anyone can help. One of the resistors is R3, the other resistor is identical to it. Look to be a 1watt pink in color metal film resistor. Thanks for any help!

[Jazz P Bass]

Can't help with a schematic.

If there are burnt resistors, something beyond them is shorted.

Check (or disconnect) the power amp output transistors.

Edit: the X4000 may be a rebadged XTI4000.
http://bee.mif.pg.gda.pl/ciasteczkow...xti-series.pdf

[pnut5150]

Thanks Jazz. I figure there is probably a bad transistor in there, just need to find out those values. I can't believe it took Crown three days to return my call and still wouldn't help.

[Jazz P Bass]

Does the X4000 use a Switch Mode Power Supply?

[pnut5150]

To tell the truth I don't know what that is Jazz

[Jazz P Bass]

A Switch Mode Power Supply (SMPS) is basically "Hell on Earth".

A 'normal' power supply has a huge honkin transformer that changes the mains voltage to a more workable secondary.
Followed by a bridge rectifier and a few 'smoothing' capacitors.
That's it in a nut shell, Linear wise.

Now enter SMPS.

The power line enters a PFC circuit, a rectifier and some capacitors.
That voltage is then switched on & off, through a much, much smaller transformer at a rate of about 15K a second.
Then that secondary voltage is rectified & smoothed.

Pain in the butt is what they are.
But very, very efficient.

Note: the Primary side of the circuit is attached directly to the mains.
Dangerous to work on.
So if you are not familiar with SMPS circuits, it is best to stay out of there.

[pnut5150]

Gotcha, thanks very much for the lesson. It does have a huge round transformer in it. So I assume it is not a switchable?

[DrGonz78]

Does it look like this?

[Jazz P Bass]

The XTI 4000 is switch mode. Take note of the dinky transformer.




The X 4000 is a plain old linear power supply.

[pnut5150]

Yea just a plain ole linear it is