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Old 2nd February 2014, 07:35 PM   #1
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Default Crest Audio LA601 Repair Help

Hello everyone!

I have a Crest Audio LA 601 that I recently purchased as 1 channel broken, I got it home, cleaned up the inside a bit and she worked fine, both channels sounded nice and powerful.

However I observed that the power lights on the amp would dim more than I thought they should on heavier bass notes.

Sure enough after about 3 sessions, about 2 hours each, one of those big Philips 10,000uf 67V filter caps went POP!!!

Now the first question, is how can I check if the other filter cap is still good, or if it is doomed to blow too. It doesn't have an obvious defect, and neither did the other filter cap. I know I should replace both, but this is my amp, and I'm cheap. I also noticed this cap has 3 legs, but it looks like one of them isn't connected to any traces, just a little pad to secure it so I assume a normal 2 leg radial cap will work.

Secondly, I see on ALL of the pcb's in this amplifier that the solder mask is bubbled up just like paint gets on a rusty car. If you just poke the solder mask a bit it chips right off the board, and there are some areas where quite a bit has chipped off.

Is this a serious issue, and if so can it be fixed? I'm almost tempted to coat all the boards in liquid electrical tape but I figured I'd ask first. I don't think it'd be much of a safety issue considering its got one heck of a thick metal case that's grounded and the outputs are dangerous as they are (pro amps can put out quite a few volts) so if it were to put the supply (I think about 60VDC) on the outputs, it'd be no more of an issue than just running it in general. I am however still a bit worried about corrosion occurring on the exposed traces on the PCB. Just let me know what you guys think.

One more question, how can I clean all the electrolyte off of the power supply pcb from that blown cap? I've never really had to deal with that sort of massive mess that that stupid cap spewed out.

I appreciate any and all help, thanks in advance!
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Old 3rd February 2014, 12:19 AM   #2
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In the mean time I'll look for caps...
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Old 3rd February 2014, 12:26 AM   #3
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Quote:
Originally Posted by TheTubeAmper View Post
Sure enough after about 3 sessions, about 2 hours each, one of those big Philips 10,000uf 67V filter caps went POP!!!
Replaced all caps including two big ones.
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Old 3rd February 2014, 01:56 AM   #4
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Replaced all caps including two big ones.
I don't think I'm going to replace more than just the two filter caps. I don't want to put too much money into this amp.
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Old 3rd February 2014, 02:59 AM   #5
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well if you go on the cheap and replace just the main filters make sure you can test it for stability.
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Old 3rd February 2014, 03:10 AM   #6
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well if you go on the cheap and replace just the main filters make sure you can test it for stability.
What exactly do you mean?

I'm thinking you mean don't sell it right away as it might not have fixed the issue. If that is what your trying to say, well, I'm not selling this amp ANY time soon.

Have any suggestion to how to clean up the electrolyte as well as if the solder mask issue is really an issue?
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Old 3rd February 2014, 03:40 AM   #7
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no stability at all frequencies as in it not going to be an oscillator
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Old 3rd February 2014, 03:46 AM   #8
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no stability at all frequencies as in it not going to be an oscillator
How exactly can I check that?

I've ran it for probably 4 hours full range with a bit of equalizer tuning before my crossovers came in and I ran it for that hour or so before it blew up.
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Old 3rd February 2014, 04:38 AM   #9
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have you an oscilloscope?
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Old 3rd February 2014, 04:38 AM   #10
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I found something quite interesting just now. I've been wondering about the existing 67V caps, as 67 isn't a normal number like 63.

I tested from center tap to one end of the winding and measured exactly 50VAC on a true-rms multimeter. Now 50 * 1.41 = 70VDC, which is over the 67VDC caps used in the power supply in this amp.

I can't really tell if those caps are original or not, the solder joints look like they may or may not be original, I just can't tell...

Quote:
Originally Posted by turk 182 View Post
have you an oscilloscope?
Yep, I have a decent amount of the usual gear. Multimeters, Power supplies, Oscilloscope...
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Last edited by TheTubeAmper; 3rd February 2014 at 04:41 AM.
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