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Old 8th October 2011, 07:26 PM   #11
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Quote:
Originally Posted by Frank Berry View Post
You can replace the amplifier for less than the cost of repair.
I know Frank, but think of all the glory I will endure if a fleabay product gets it back running for $32 and some soldering time.
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Old 8th October 2011, 07:58 PM   #12
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0-if the "crackling" is not happening randomly but all the time then it should be easy
1-does the unit smell when operating ?
2-monitor the supplies (with your scope) and any relay control signals
3-check the power resistances or diodes on the power transistor emitters (?)
4-listen to the output of the pre-amplifier with an headphone (solder wires)
5-report
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Old 8th October 2011, 08:00 PM   #13
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Replacing all the outputs to cure crackling noises makes zero sense. IMO, the service people are clueless, or the amp design has some very unusual issues that only they know about. I just fixed a Peavey with many problems, including a crackling problem. It was a bad ground connection in an IDC connector where the panel input board attached to the main circuit board. I've also had crackling problems when small signal transistors were going bad. The plastic rod, a certain amount of shaking and banging and some freeze mist might be your best place to start. I'd put most of my money on a mechanical issue like connectors or bad solder joints, but save a little to wager on the odd semiconductor failure. Use bright lights and a powerful magnifier as well.
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Old 9th October 2011, 01:47 PM   #14
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Quote:
Originally Posted by pierreohm View Post
0-if the "crackling" is not happening randomly but all the time then it should be easy
1-does the unit smell when operating ?
2-monitor the supplies (with your scope) and any relay control signals
3-check the power resistances or diodes on the power transistor emitters (?)
4-listen to the output of the pre-amplifier with an headphone (solder wires)
5-report
Quote:
Originally Posted by Conrad Hoffman View Post
Replacing all the outputs to cure crackling noises makes zero sense. IMO, the service people are clueless, or the amp design has some very unusual issues that only they know about. I just fixed a Peavey with many problems, including a crackling problem. It was a bad ground connection in an IDC connector where the panel input board attached to the main circuit board. I've also had crackling problems when small signal transistors were going bad. The plastic rod, a certain amount of shaking and banging and some freeze mist might be your best place to start. I'd put most of my money on a mechanical issue like connectors or bad solder joints, but save a little to wager on the odd semiconductor failure. Use bright lights and a powerful magnifier as well.
Thanks for responding Pierreohm and Conrad
The unit still has its new condition smell and looks like it is new as can be seen in the picture. It has never moved from my house but twice to the same authorized Crown repair dealer. It has been pampered except when it reached their shop. All the more reason that I would rather set it on fire than bring it back.

I don't have a scope. I have a Digital Multimeter.
Output pre-amplifier no problem with a headphone.
As I said in the previous posts, this is the second time they pin pointed to the transistors and now that I have the mother board exposed, I can see the soldering done by human. I don't know if you are able to see the excess thermal compound residue left all over some of the transistors.
Let us assume that, because they were recommended by the Crown Official Site, they know what they are doing, let me post the estimate for everyone to see the diagnosis.
I may have not explained the symptom properly.

When the power is put on, it makes this buzz sound as if a jack is bad. When the musics comes on, it sounds like a blown speaker unable to handle volume on both channels. I can hear the music, but with some kind of interference and not providing the juice required.

I have read that once a few of the transistors go bad, all of them need to be tossed eventually they lose their integrity over time. These were changed before by them for the same symptom supposedly. Does it that sound like the function of the transistors. Please take a look at the estimate and what they were about to change. The discoloration of the last open my wallet surgery.

Click the image to open in full size.
Thanks!

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Last edited by MaitreG; 9th October 2011 at 02:03 PM.
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Old 9th October 2011, 03:30 PM   #15
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Power transistors usually fail shorted, so the amp would blow fuses/breakers or activate some sort of limiting. That's not your symptom. Small signal and passive components can do anything- that's where I'd be looking. In all honesty, they're charging some markup on the transistors, but their labor rate is quite fair. Considering unpacking, setup and cleanup, it takes me about a full day to sort out and document an amplifier if it has subtle problems and if I'm being as thorough as I like to be. That's why many things aren't worth fixing- labor is too high. Factory authorized service is good unless it isn't. You might want to consider a skilled tech someplace else.

BTW, transistors don't "lose their integrity". You put 'em on a curve tracer and they're either good or not.

(I notice the condition is marked "fair" which doesn't seem quite fair if it was perfect when they got it the first time.)
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Last edited by Conrad Hoffman; 9th October 2011 at 03:34 PM.
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Old 9th October 2011, 06:39 PM   #16
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6-can you tell us the AC voltage on all the DC supplies and grounds, that should give an idea of the ripple.
7-idle, are the bjts getting hot ?
8-do the headphone test (solder) further down the power path, stop when you find something suspicious
9-sure any kind of protection is not triggering and degrading the sound?
like Conrad Hoffman said triple check the input stage
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Old 9th October 2011, 07:02 PM   #17
Mooly is offline Mooly  United Kingdom
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Not spotted it in the above posts, but a manual is here if needed,
Free Manuals User / Service / Schematics for Download | HiFi Engine

I agree it doesn't sound like an output transistor failing... they don't fail like that but other types can and do go intermitent but that would be more like a catestrophic failure and result in intermitently high DC offsets. Little caps can be a problem but I'm afraid we are just guessing.

With a lack of test gear/scope it may be a bit ambitious to undertake DIY repair as any mishaps could be costly.
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Old 9th October 2011, 07:19 PM   #18
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Default How much for MJ15024/4!!!!!

They seem to have diagnosed without seeing the unit and are charging you maybe 10x cost on those transistors. They haven't a clue, and don't let them touch it. If you were in UK I would have pointed you in the direction of Lee Basham as that amplifier used to be the C Audio GB602. You could try posting on SpeakerPlans.com - they might know a service tech nearer you to help you out.
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Old 9th October 2011, 07:50 PM   #19
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I'm nowhere near some of the guys here when it comes to engineering experience, however I have a lot of experience talking with Crown customer support. Just call support and ask for Kevin Gring. He'll have a bunch of helpful tips that will enable you to walk through the whole thing until you get the amp repaired.

I know that it sounds crazy, but I spoke with him for about half an hour a day for over a week and we were eventually able to narrow down the problem to one section of the circuitry and then a particular bad resistor (my Comtech 400 was producing very garbled audio)! Before starting, I was an amplifier nub.

At least for me, Crown offered unlimited free support even though I purchased my amplifier from Ebay.

Good luck!

By the way, you can find the schematic, etc here:

Discontinued Amplifier Products
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Old 9th October 2011, 09:15 PM   #20
imix500 is offline imix500  United States
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Just out of curiosity why didn't you sent the amp to Indiana? Crown factory service is better than many I've dealt with . I send dozens of amps to them every year and they are always fair and honest. They will often even fix design issues that go out as service bulletins for no charge on parts.
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