Repairing Crown XLS-602 amplifier - need help

[ViperZ]

Hi all,

A Crown XLS-602 has failed in a local church, so I'm trying to troubleshoot it and get it back up and running.

All power supply voltages are present. No speakers and no inputs connected (happens with connected load/input too). Level potentiometers are set at zero on both channels. So far so good. Let it warm up for about a minute. Then raise the level on one of the channels to any position, and protection kicks in within 1-20 seconds, holds for about 5-10 seconds, then returns to normal.

What could cause this problem? Thank you.

 

[petehall347]

i would first check all board connections and also look for cold solder joints .

 

[ViperZ]

For a pro amp, it's surprisingly difficult to take apart. It also uses those nasty ribbon cables, which are soldered and glued on each end, so they cannot be disconnected. I just unscrewed all boards, so I can at least lift the mainboard out of the enclosure to look at solder joints on the bottom.

 

[SoCal Sam]

No click could be DC offset problem or protection circuit itself.

 

[ViperZ]

It is clicking...

So I measured DC offset on the outputs of each channel. Put my meter onto a trigger, because it spikes and protection shuts off the outputs. When pots are at 0, DC offset is 10mV on each channel. When I start moving the pots, DC starts jumping between 0.5V and 3V, stop moving - goes back down to 10mV. But sometimes it just spikes very high (protection instantly shuts it off, I was able to measure 8.8VDC, but it's obviously much higher).

Does it sound like each channel has blown output transistors?

 

[SoCal Sam]

Just a guess before the techs chime in...check all solder joints around the protection circuit and DC trimpot. Change trimpot. If outputs were shorted, you would have blown fuse which is not the case.

 

[ViperZ]

There are no adjustment trimpots on this amp... There are also two sets of protection relays - for outputs and to shut off power supply. Both get triggered on spikes.

 

[whoaru99]

If no relief here try the Crown forum.

 

[RWood]

If this one is like my XLS 402 the hot connection from the speaker terminal is a rigid connection to a pcb. Every time a speaker is plugged/unplugged it puts a little stress on that connection at the pcb. On mine, this did not result in the protection circuit engaging and other symptoms you have, just intermittent sound. But I wanted you to know, while you have it open you might check it out.