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Old 2nd June 2011, 07:09 PM   #1
msquicc is offline msquicc  United States
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Red face Crown 602 XLS Power Issue

Before I ask, I know the risks involved in opening a high power amplifier. I know sending it to an authorized repair shop is the best (and most expensive, possibly more so than buying a new amp) option. I'd like to fix it myself if possible for several reasons.

Now that I have that covered, my amp has been working fine.

The other day it was running for a while and suddenly made a furious ticking sound (like a zapping sound). ALL FOUR lights on the front (Power, Fault, Clip 1, and Clip 2) flashed simultaneously with the sound. It lasted for maybe 2 seconds tops. Immediately following, the unit powered off. All four led indicators are off at this point (and have not turned back on at all since). Not enough time for me to turn it off, but I hit the switch a second later or so. I tried the circuit breaker just in case, but figured there's no way that was a breaker. Smelled a burning type of smell after all that too.

I tried powering the unit on a couple minutes later: nothing.
Tried again w/ speaker disconnected, new power cable and no input xlr: nothing again.

Tried a day later just for s...n giggles with speakers plugged in and no input signal. Surprised me when the speaker started trembling a bit and I turned it off immediately.

I've done some looking around the web for posts n such. The circuit breaker seems to be fine. Did not pop and when I measure the resistance I got .2 ohms. Seems to me the breakers fine. Same reading past the switch, so that's good.

I just tried plugging it and turning it on for a brief second to see if the red leds on board light up and they don't. (figured) after a couple of seconds, I turned it off. Again noticed a burning smell coming from somewhere right around the power supply / transformer area. (pretty sure)

Anyway, the speaker terminals seem to be ok on the ohm meter. Channel 1 comes up as about 280 kilo-ohms
Channel 1 was the only channel being powered. Amp is being used to power a single subwoofer.

Does that mean anything? Seems to me like that shouldn't be a problem, but I'm not sure.
Channel 2 doesn't even produce a reading, so I think that's even better.

I think I've included all the detail possible at this point.
What are the next steps I should take in troubleshooting the components? I'm guessing it's maybe the transformer itself, since I'm pretty sure the amp has a soft start which normally makes a click when it turns on. That is not happening either. Silence, no LEDs are lit up, and last I checked it sends a slight thumping/trembling/low frequency signal to the sub-woofer. (not that I'm gonna try that again hahaha)

Thank you in advance for anyone who can help me out with this. I do have a schematic, but I'm pretty sure there are several modifications of this amp with the same exact model number.

Thank you everyone!
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Old 2nd June 2011, 07:42 PM   #2
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I would disconnect the transformer from the amp and see if I was getting corrrect AC volts out on the transformer.
If not the transformer it could be the bridge rectifier or the smoothing caps gome short.
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Old 2nd June 2011, 09:55 PM   #3
msquicc is offline msquicc  United States
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Smile Transformer Measurment

Nigel,

Thank you very much for your quick and polite response!

So I put my multimeter on the transformer's secondary winding taps.

There's 5 of them. I uploaded the schematic in pdf format if you care to further assist. I'm hoping I tested the correct leads. I didn't test the black one against any of the others.

Results:
red/orange: 140V ac
white/yellow: 38V ac

I think this means the transformer is good. The smell doesn't happen when the transformer is disconnected from the board.

I'm at the bridge rectifier now. The smell's back again now that I've reconnected the transformer.

Maybe I haven't thought about it for long enough, but I'm having some trouble figuring out which points on the rectifier to test.

Any ideas?


Also, which are the smoothing caps you're suggesting? The big ones (C1,2,4,&5)?
Attached Files
File Type: pdf Crown 602 xls main schematic.pdf (148.6 KB, 185 views)
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Old 2nd June 2011, 10:02 PM   #4
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Look for DC out on the rectifier on the pins marked + and -
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Last edited by nigelwright7557; 2nd June 2011 at 10:17 PM.
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Old 2nd June 2011, 10:18 PM   #5
msquicc is offline msquicc  United States
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Default Rectifier

Yea, I esentially tested across one of the capacitors on the rectifier (or around it?) I came up with about 1.5v DC

not sure if I tested the right points...
I'm pretty sure the schematic is saying 250V at that point...

should those points work for that?
I'll give it another go as well
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Old 2nd June 2011, 10:49 PM   #6
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1- this is not a class D amp so it is in the wrong category

But that aside. when these amps blow, IE short out the output transistors, which is VERY common..it shorts the power supply to ground. they will not power up but the PTC's wired to the transformer primary get VERY hot! the dum things wont even blow the fuse!


and when they blow, it back feeds up the feedback path and pretty much blows every transistor on the board. take my advice, just shotgun them all they are cheap.

ALSO, check the speaker relays, they will melt those relays in a heartbeat! 9 times out of 10 those relays are burnt! and when burnt they will short to ground and blow the newly rebuilt amp up...don't ask me how i know this....

These amps were made by C-Audio in Europe. in fact the boards are labeled C-Audio. Crown has been struggling trying to build a low cost amp to compete with the behringers etc. they got massively burned by the CE series line disaster (but of course they won't admit that.) but a 90% failure rate = disaster! So crown decided to outsource the boards for this model. and frankly they are only marginally better than the CE series. for a small light duty PA they work fine, but they just cant take any sort of abuse.

The plus side is they are fairly easy to work on. check for open or burnt resistors, shorted diodes and i will place a large bet you have blown output transistors. just order all the transistors for that channel, you will need them and don't trust any that still check good. I have rebuilt too many of these now and have learned my lessons well.


Zc
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Old 13th June 2011, 09:39 PM   #7
msquicc is offline msquicc  United States
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I don't want to take the board out if I don't have to.

Not a big deal, but I figured I'd ask first.

I tried to take out a transistor or two and they're in there really well. theyll move side to side a bit (so they're not adhered to the heat sink for any reason) the heat sink even slides underneath them and moves freely but the transistor is holding it attached to the board.

Hope this isn't a silly question, but are the transistors soldered to the board?
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Old 13th June 2011, 10:04 PM   #8
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I've had one of these sitting under the bench for a few months now, completely fried zobels, and a few charred components on the main board as well. Frankly, I wasn't planning on repairing it at all, but reusing the PSU and case with one of the decent looking 500W projects here on the site.
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Old 13th June 2011, 10:22 PM   #9
msquicc is offline msquicc  United States
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I can't find anything charred, without taking the board out. I'd imagine I'd be able to see something from the top. I really don't THINK it's a disaster. I'd really like to go through the process of fixing it myself becuase I enjoy this stuff a lot. Like to build some too at some point, and if I run into some money soon I'll just send it out and have it fixed, but I really want to do it.

I guess I have to take the board(s) out. It doesn't look fun detaching the wiring from the front level pots (did i get that right? haha) Might even wind up finding a burnt something? hope not in a way hope so in a way lol

1) thing thats getting me is where to test the dc voltages.
the fact that NONE of the led indicators come on (and i can smell something when it's plugged in and on) tell me that it's a power problem, not necessarily a problem w the output section

I could be wrong. I'm definately considering both options. I tested the transformer as i mentioned and the voltages seemed a bit high. I got a reading of about 140v ac at the point where my schematic (which COULD be inaccurate because I've heard there were a few revisions with this amp) says UP TO 65VAC

hmmm is that a problem?
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Old 13th June 2011, 10:32 PM   #10
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well..ok...you really need to find someone to HELP you fix this if you are asking these kinds of questions. YES the output and all transistors are soldered to the board. the board has to come out.

when the output transistors blow, it shorts out the power supply. the soft start device in series with the transformer gets hot. that's what you are smelling. no front panel LED's will light up. this is normal for this amp under these conditions. IE when a channel fails and the output transistors short.


Please be careful. there are lethal voltages inside. I would strongly advise finding someone near you that can help you if you intend to fix this yourself.
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