I was using headphone output (1/4 jack) on my Yamaha receiver (about "-25 dB" was the volume setting) to XLR input on the XLS 602 amp.
Is that a bad idea?
Testing one channel at a time and then a loud band and sparks flew out of the back where the fans are. I think this happened twice. The channels I was testing when this loud pop happened, no longer works.
What do you think exploded? 😀
Only thing I see there are MJ15024 and MJ15025 transistors.
Everything looks okay. Top of one of the heat sinks next to the top cover looks like something exploded there, but I don't see any electronics near there.
I have a bunch of transistors, maybe I can fix it? I think I might still have some MJ15024/25 also.
Maybe I shorted the cover to the heatsink? I think I was pressing down on the top cover to mess around with the back of the amp.
Is that a bad idea?
Testing one channel at a time and then a loud band and sparks flew out of the back where the fans are. I think this happened twice. The channels I was testing when this loud pop happened, no longer works.
What do you think exploded? 😀
Only thing I see there are MJ15024 and MJ15025 transistors.
Everything looks okay. Top of one of the heat sinks next to the top cover looks like something exploded there, but I don't see any electronics near there.
I have a bunch of transistors, maybe I can fix it? I think I might still have some MJ15024/25 also.
Maybe I shorted the cover to the heatsink? I think I was pressing down on the top cover to mess around with the back of the amp.
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It's possible that the heat sinks are indeed live, and that you shorted one or more of them
to the cover when pressing down.
You could measure the DC voltage between the sinks and the chassis to see. Check the rail fuses
in case one or more fuses are blown. If you are very lucky, that may be all that is wrong.
to the cover when pressing down.
You could measure the DC voltage between the sinks and the chassis to see. Check the rail fuses
in case one or more fuses are blown. If you are very lucky, that may be all that is wrong.
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Yes, those heatsinks are not isolated from the transistors so you shorted one rail directly to ground, causing an explosive spark from the filter caps dumping all their stored energy into the lid and heatsink, spot-welder style.
I think you need to think of a way to prevent this happening again, its a design lapse (I presume the lid is perforated making it tricky to just add some kapton tape on it internally?)
The top of the mounting bolt for the toroidal transformer needs insulation too.
I think you need to think of a way to prevent this happening again, its a design lapse (I presume the lid is perforated making it tricky to just add some kapton tape on it internally?)
The top of the mounting bolt for the toroidal transformer needs insulation too.
I would get some Kapton tape with adhesive on one side, and cover the tops of all of
the heat sinks with that. Fold it over each side so that no contact with the cover is possible.
https://www.amazon.com/dp/B07S2219C...uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl
You should be able to find a rubber foot to go over the toroid bolt end.
the heat sinks with that. Fold it over each side so that no contact with the cover is possible.
https://www.amazon.com/dp/B07S2219C...uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl
You should be able to find a rubber foot to go over the toroid bolt end.
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Oh yes, they are horizontal heatsinks aren't they - perhaps the lid is solid then, if there's lateral airflow, in which case I'd put the tape on the lid to avoid compromizing the heatsink performance (and less likely to peel off due to the adhesive melting).
Kapton with silicone adhesive is often used for power electronics, where heat sinks get really hot.
I've used it for a long time, it won't come off.
The air goes front to back, so there's no holes in the top. I suppose you could attach some Nomex
to the underside of the top cover and forget about it. Even the thinnest Nomex is tough and will
resist perforation really well, and is flame-resistant.
I've used it for a long time, it won't come off.
The air goes front to back, so there's no holes in the top. I suppose you could attach some Nomex
to the underside of the top cover and forget about it. Even the thinnest Nomex is tough and will
resist perforation really well, and is flame-resistant.
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Okay thanks, I'll check the fuses.
Which ones are the filter caps?
Any way to guess what could be defective or not really?
The 4 big capacitors on the lower left corner. Chances are they are still good, sparking them ONCE won’t generally hurt them. The live heat sinks means you shorted the power supply, not something internal to the amplifier. Big transformer supplies can handle momentary overloads - unlike a switch mode that likely would have been destroyed. The only problem you may encounter would be collateral damage from a single rail collapsing suddenly with the other side still powered - it could result in blowing something, even in the small signal circuitry. A sensibly designed circuit wouldn’t fail due to this but this amp was not the best example of Crown engineering - those days were long gone a decade ago.
Replace the fuses, fire it up on a dim bulb, and then make an assessment. Probably 75% chance of it just working with no other fiddling.
Replace the fuses, fire it up on a dim bulb, and then make an assessment. Probably 75% chance of it just working with no other fiddling.
yeah just check the fuses, fire it up on a series bulb limiter/ dim lamp tester
test the outputs have no dc offset.
and add a insulator to the lid so it doesn't happen again.
aka duct tape, kapton, rubber, vinyl etc etc
you can see a arch over zap on the heatsink in the photo
test the outputs have no dc offset.
and add a insulator to the lid so it doesn't happen again.
aka duct tape, kapton, rubber, vinyl etc etc
you can see a arch over zap on the heatsink in the photo
Vinyl is inflammable, Kapton and Nomex not so much.
If you can, get a piece of the white sheets they use in motor winding. Sticking those is difficult, as the adhesive tapes may degrade, use the tape intended for high temperatures, like 150 Celsius and higher.
Thin sheet of PCB material or even Formica will be better insulating in the long term.
Use screws, or epoxy to hold in place, few dabs are enough.
If you can, get a piece of the white sheets they use in motor winding. Sticking those is difficult, as the adhesive tapes may degrade, use the tape intended for high temperatures, like 150 Celsius and higher.
Thin sheet of PCB material or even Formica will be better insulating in the long term.
Use screws, or epoxy to hold in place, few dabs are enough.
Yes that is a bad idea but that is not why it blew up.
With this connection you are injecting an unbalanced stereo signal into a balanced mono input, that is a bad idea because the balanced circuitry will cancel everything common to both channels.. which is usually all the low frequency content. So depending what the amp is driving this could be completely counter productive.
Chances are it was split into two channels and driving the two amp channels unbalanced. The real problem is the signal might be way too high coming out of the HP jack. Some amps have a dedicated chiplifier to drive the phones, others just put a resistor from the main amp’s output directly to the jack. Under light load you get the amp’s full output voltage. That’s too high for an op amp stage, which is used to derive the balanced input. You could clip the front end at a relatively low output from the main amp, before it gets to the volume control on the PA amp. If you were counting on being able to drive the receiver and amp up to clipping around the same point on your main volume control, you won’t be able to. Unless you *attenuate* the HP jack signal first. A shunt resistor of appropriate value (chosen by experiment or measurement) may be all that’s needed. Perhaps that has been done already? I doubt it would hurt the op amp to overdrive it with the current limiting resistor from the HP jack, but it would sound pretty awful unless it’s turned down really low and the noise floor might be objectionable.
I use the earphone jack of portable radios & CD players to drive power amps directly, all the time. I do turn them down to about 1/3 volume as they clip and sound bad putting out 7 vac output as many will. The current output of those products is not high enough to damage an amp input.
But a power amp headphone jack, if is capable of 3 watts or more, can burn the input resistor of the power amp as the input is clamped to the PS rails by the protection diodes. Peavey put 1/10 w 100 ohm resistors in the input of the CS800s to blow up if somebody plugged a 25 W guitar amp in that jack. They were burned out when I bought the product from a local bar band leaving the road. 1/10 watt resistors are cheaper than fuses, no liability insurance or lawyers that have to be paid off.
But a power amp headphone jack, if is capable of 3 watts or more, can burn the input resistor of the power amp as the input is clamped to the PS rails by the protection diodes. Peavey put 1/10 w 100 ohm resistors in the input of the CS800s to blow up if somebody plugged a 25 W guitar amp in that jack. They were burned out when I bought the product from a local bar band leaving the road. 1/10 watt resistors are cheaper than fuses, no liability insurance or lawyers that have to be paid off.
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1/4" jack (headphone output on Yamaha receiver) to XLR does sound weird.
Problem was with "dual/bridged" switch; it was dirty and it was on "bridged" for some reason.
Top plate is about 6mm above the heat sinks, so not sure how I crushed it down to the heatsink. Maybe need to loose weight 😕
I am pretty good at breaking things though 😀
Sound works on both channels.
Problem was with "dual/bridged" switch; it was dirty and it was on "bridged" for some reason.
Top plate is about 6mm above the heat sinks, so not sure how I crushed it down to the heatsink. Maybe need to loose weight 😕
I am pretty good at breaking things though 😀
Sound works on both channels.
