Crown DC150A amp overheating

I have finally determined that a burning smell is coming from my Crown amplifier.  It sounds OK, and the IOC lights do not come on, except at shutdown which is normal. So I need to debug the cause of this DC150A  overheating.  Without going at this blindly, I was wandering how I can address this in a systematic fashion?  I've found a flowchart online that is useful and it said that bad connectors could cause this (impedance mismatch), so I have ordered some better adapters for the  RCA to ¼  phono jack input connections.  The ones I am using now are a bit small for the female  ¼ inch inputs.  In the meantime, I am wondering if I should take off the covers and take a look?  Not sure what I should be looking for though.  Any ideas on how to proceed with this?

https://www.manualslib.com/manual/33722/Crown-133472-1a.html?page=26

I have also added a fan and have given the amp a little more space for cooling.... this has seemed to help a bit.

musika said:

I am wondering if I should take off the covers and take a look? 

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Heck yeah ;D

Maybe you could smell better where the smell is coming from...

You say it smells like it's overheating? But the amp isn't overheating?

Pretty old unit and it could be some dried up components????.....burning dust? old thermal paste.......????

Best to take a look before anything gets worse I'd imagine....

You can always post pics once you get inside and maybe someone can help more......

Good Luck!

I hear those sound great.....

Will take a look...it is used  quite a bit so I doubt the dust explanation, but thermal paste is a good possibility.  Great amp, I've owned it for many years, bought it new.  I think I've replaced the power on switch and pilot light up until now.

Wow that's awesome.....
I have a newer/ older Com Tech and it's great....never any issues.....still going.....

Can't say that about an XLS series I have.....Has a goofy input problem I have yet to investigate....saw the smd parts and decided to wait a while..... ....Although I have to admit it was problem free for several years.....not decades though....lol

Good luck!

Make sure to post any updates....

The good lord gave you fingers.

I'm just getting over a 3rd degree flesh-burn from my Honda brake. So some care is wise.

The DC150 is not the most vicious basket of snakes in the rack, but the insides can deliver a jolt, especially if you get into the 120V wiring. Get the covers off, put them back loose. Work it until it stinks. With the music still playing (to discharge the caps), yank the power plug out of the wall. When the music fizzles out, yank the covers and start feeling inside.

Some things are supposed to get warm. Big power resistors, obviously heat-sinks, maybe PT. If you were not filling Yankee Stadium, in a DC150 none of these will be too hot to hold. It has to be hotter than that to stink. So when you find an "Ouch!", you may have found your stinker.

PRR said:

With the music still playing (to discharge the caps), yank the power plug out of the wall. When the music fizzles out, yank the covers and start feeling inside.

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Great tip!

The size of the cans in my Crown and a couple other amps I have  are intimidating for sure......

Sucks about your burn.... I was messing around with an old pressure washer with a big old Honda engine one morning and went to lean down to adjust something. To balance myself I mistakenly grabbed on to the exhaust that was missing it's shield.....it looked like the filter housing that was next to it which would've been cool....... Mr. bubble hand for a couple of weeks after that..... Pretty funny that it was caught on my camera system and, after watching it again, it was like a split second before you could see me react but, you'd think I left my hand on there for days the way it looked......And felt......

Way up on the pain level threshold for sure.....

Come to think of it, I really should get a shield for that thing before someone else gets hurt...

scott2000 said:

Great tip!

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PRR's tips usually are.

The size of the cans .... are intimidating for sure......

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You just reminded me of an old girlfriend. 8)

A lumber marker crayon melts at around 160F, and makes a good heat test probe. A china marker should work too, I don't know the melting temperature of those, but I suspect it is similar.

Gene

Gene Pink said:

PRR's tips usually are.
You just reminded me of an old girlfriend. 8)

A lumber marker crayon melts at around 160F, and makes a good heat test probe. A china marker should work too, I don't know the melting temperature of those, but I suspect it is similar.

Gene

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Yes! Always great advice....Always very generous to help us who aren't in the know....

Ahh...The cans.....

Guess we're even now.... thought I'd all but forgotten her.....

Great tip on the crayons!! My fingers thank you.....

PRR, I call that the "digital thermal probe"

If you lick your finger first, the instant steam from touching hotter than 100'C devices will make noise and could prevent a worse burn (or losing your fingerprints). But it will also make you more conductive to electricity.

One obvious cause of excess heat in class AB amp (that still works) is output stage class A bias.

JR

One obvious cause of excess heat in class AB amp (that still works) is output stage class A bias.

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Tried to do a little research on this idea....

Are you saying that transistor malfunction is more likely the cause of overheating (in other words)?

I'd be interested in this too.  I think transistors can get hot if there's something else wrong, like if it's feeding a bad op amp  or something...........Doesn't really mean the transistor is malfunctioning....yet.....????

A lumber marker crayon melts at around 160F, and makes a good heat test probe. A china marker should work too, I don't know the melting temperature of those, but I suspect it is similar.

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I like this idea of a heat test probe better than my finger!

Finally got around to this... pulled the power cord as PRR suggested then tested for heat. What I found was that one particular power transistor marked in red was running hot.  Still not certain what is the cause.

That looks like a driver transistor, if it is getting hot the power device it is connected to is probably bad , making it work too hard.

Check all the power devices (to-3s).

JR

The manual I have says that the driver transistors are 2n3585.  But the part number surely shows 3295.  OK. This is Crown's part number.

Anyway, I need to be able to disassemble those round grey parts to get to the circuit board on the other side.  They have long screws through them holding on the housing behind.  I am not sure about these... don't know what they are and I want to make sure I don't damage them, by unscrewing those.  They have the reddish washers on the top.

Page 21 of the service manual part 2 shows Q113 bottom left, and Q213 bottom right...... Those fit the circled transistors if I'm reading it right....I tried to upload but can't.......

Is it best to test these TO-3's pulled from the circuit or can I test in place?

You can test in circuit ( at least I have) but, don't trust a bad reading (on anything) until you verify after pulling it.  I had a couple bad resistors on another amp that would cause the transistors to open and close when probing, making me think the transistors were bad.....

Hopefully someone can help more and, if you can get the schematic posted, it'll get someone closer to helping more I'm sure.....I'll see if I can get it posted....

Good luck!!

Power transistors generally fail as a short from collector to emitter, but that would not give the symptom you see,, so I suspect maybe an open base, or soft failure...

Check all the power devices for base emitter diodes, base collector diodes, etc.

JR