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Crown XLS602 - Bad Channel
Crown XLS602 - Bad Channel
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Old 13th September 2018, 06:45 PM   #1
mortron is offline mortron  Canada
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Default Crown XLS602 - Bad Channel

Recently had an amp give up on one channel. It's still got an audible signal but it's whisper quiet at best. Turning it up doesn't increase volume, just distortion. I have tested with several different speakers and sources and believe it's beyond the inputs because I've cleaned the pots and they both show a signal on the LED. I not see any broken connections or leaky caps.

I believe someone dropped it while moving it, but it's just speculation and they deny dropping it.

Anyone had similar experiences with a channel like this? Is this a typical symptom of a specific problem?
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Old 13th September 2018, 07:56 PM   #2
nigelwright7557 is offline nigelwright7557  United Kingdom
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If its been dropped could be a cracked pcb.
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Old 13th September 2018, 10:55 PM   #3
MAAC0 is offline MAAC0  Portugal
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I've seen a similar problem on an amp and it was a high wattage open resistor. When turned Volume up Clip led would light rhythmic with the sound.
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Old 21st September 2018, 11:28 PM   #4
mortron is offline mortron  Canada
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Interesting theories. I have been assured it was not dropped so will place trust in them for now.

Signal is playing through. The clip LEDS don't light up. The front lights make it look like business as usual.

Somewhere between using it and bringing it to their place it just quit. Not sure if it was when we hooked it back up something different happened or what. My next thought is to clean the bridge/stereo switch just in case. Pots got cleaned. One feels a bit different but recall it always feeling so.

Would the level LEDs only be showing the signal after the pots? Or is that not how the signal chain flows?

They sure don't make these things easy to work on. Everything is in my way haha.
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Old 24th September 2018, 10:17 PM   #5
MAAC0 is offline MAAC0  Portugal
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Can You swap connectors ? That will tell You if the fault is on the input preamp or the power amp. It can be also a broken signal or flat cable.
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Old 25th September 2018, 10:52 AM   #6
TBTL is offline TBTL  Germany
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The schematic is available online on Elektrotanya. Measure till where the signal gets and measure supply voltages. Use the other channel as a reference.
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Old 25th September 2018, 11:20 AM   #7
mortron is offline mortron  Canada
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It's not the preamp. I have it down to the one channel being faulty. I've ruled out everything but the amp.

I am going to start comparing sides of the circuit and see where things start to differ and go from there. Sadly finding the time is the trickiest part of diy.
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Old 25th September 2018, 11:56 AM   #8
ledman is offline ledman  Germany
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Looking at the picture in this thread
Crown XLS 602
It seems like to the top right are testpoints or a footprint for an unpopulated test connector (maybe, i don't know, it's too low res to tell much)
might make your job at measuring what is going on easier
You could email Crown and ask them for a service manual, they typically describe where testpoints are and how they should behave

I don't know how experienced you are with poking around in power electronics, but i would recommend you wear some rubber gloves and mind where your hands are, you'll be troubleshooting live equipment and this thing has two heatsinks right next to each other, one chilling at +95Vdc and one at -95Vdc.
Touching just one won't do anything but there's 190Vdc of pure pain across those heatsinks that are easy to bridge out with the palm of your hand.
Especially if you got a ring on your finger, this thing delivers 1200W into 8 Ohms bridged, don't want to know what the peak into basically 0 Ohms is.
Probably loud.

As previously stated, try internally swapping the inputs around and measure all the supply voltages, report back on results and we can help more.
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Old 18th July 2019, 07:19 PM   #9
delta362 is offline delta362  United States
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I just repaired one of these (XLS602D, though front panel only says XLS602) this week. Channel 1 worked, but Channel 2 did not. Signal made it to C124 and C224. Signal was lost at Q202 base. I checked the diodes and transistors in all directions for both channels to see if I could find any differences. Channel 1, which works, had D100, Q104 and D106 all providing normal readings in the functional direction, and a couple volts in the reverse direction. Channel 2, which was not working, had correct readings in forward and as expected for a component, blocks in the reverse direction.

I continued to check all other components on the board and they all matched between channels. I finally solved it. R205 ended up being an open resistor. There were no signs of damage to the resistor, leads, board, broken traces, burned components or anything else. That's a first that I've seen this particular failure, but it explains the lack of channel. After replacing R205, now D200, D206 and Q204 read the same as channel 1. Powered up and tested and the amp is back in business.

Last edited by delta362; 18th July 2019 at 07:28 PM.
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