Can LM3875 blow up?

[velikan]

Hy.

This is my second post about the same problem to this forum. First time I had sam difficulties with a authorisation for this forum. Now I hope that new thread will be open.
So, this is what happened. Yesterday I completed my first ganiclone based on LM3875 with unregulated supply (http://www.geocities.com/rjm003.geo/...io/diy_gc.html). I listened it for a couple hours without any problems. I must warn you that I have regulated transformer as the source for toroid just for safety reasons.
So, today when I started to power it up again I heard a strange brum from the speakers. As I rise the voltage the brum was louder and louder. I turn the thing off, disconect the speakers and try again. I have two instruments for current and voltage monitoring on output of regulated transformer. Previously I noticed that after 60 V LM starts opetating. I was slowly rising voltage and everything was ususali until I crossed 60V. Then LM take unusual high amount of current so I quickly turn it off. I touch the boh LM’s and the one was HOT!
I put some smal voltage and inspect the circuit and there it was: complete Vee was on speaker output! Ofcourse, even I first thinked that some sort of short circuit was the problem. But, after checking the circuit (and rememer, I left it yesterday in operating state!) I noticed that there was low resistance between pin 4 and 3 (10 ohms). I wanted to inspect the circuit in operating state so I applied a 62 V and quickly measure the voltages. And there it was. Vee was –9 Vdc and speaker output was on –7.5 Vdc. Some current made that voltage drop and that was the soruce of the overheating. Other LM didn’t have that problem. His resistance between 3 and 4 was infinite. I checked the dc voltage on the input and there was none.
So, what can be the couse of this? Rember, I left it yesterday in operating state and today just switch it up! I can imagine what would happened if I put it on network voltage! BUUM!
I searched this forum for similar expirience but I havent found any. Can LM be destroyed or I got one bad example and I can get replacement?

[Tekko]

Yes LM3875 can blow up. I have videos of how i blew up a pair.

[indoubt]

Same here, just swap V- and V+ and they will smoke. Aaah!, don't do your soldering late at night (like I did)

[pinkmouse]

Oh yes: Bang!

[velikan]

Originally posted by indoubt
Same here, just swap V- and V+ and they will smoke. Aaah!, don't do your soldering late at night (like I did)

But I didn't do a thing!
Yesterday I left it after listening and today's what do I have?
What could be the cose?

[moamps]

Originally posted by velikan
....What could be the cose?...

Sometimes amps don't like slow turn on.
Especially if load is present.

Regards,
Milan

[Tekko]

When you try to blow a LM3875 on purpose like i did you will find it nearly impossible due to the sPiKe protection, but accedently its easy. Heres my LM3875 destruction station videos: http://hififorum.knaak.dk/Tekko/lm3875/ They finally died when i shorted the transformer that you can see in the videos with my multimeter, was going to measure volts but i forgot to turn it to volts so it was amps instead.

[velikan]

Originally posted by moamps


Sometimes amps don't like slow turn on.
Especially if load is present.

Regards,
Milan

Hmm, I just heard that some overvoltage transients may be couse for that low resistance between Vee end speaker output. Yes, it may be the case that I swiched the circuit off the 220 V. I am told that I must put 0.1uF od power line for that high frequencies overvoltages.

I am sending one photo in case that someone may find it interesting.

[orkaniusz]

A few days ago I coused my LM3886 to blow up. Its V+ pin was broken.
After I had examined carefully what had happened, I found the reason: Isolation between heatsink and LM was not perfect. I measured resistance between them and it was beyond the range of my multimeter, but not after mounting the heatsink and cirquit in the chassis....

It's allways safer to use TF package.

[velikan]

Originally posted by orkaniusz
A few days ago I coused my LM3886 to blow up. Its V+ pin was broken.
After I had examined carefully what had happened, I found the reason: Isolation between heatsink and LM was not perfect. I measured resistance between them and it was beyond the range of my multimeter, but not after mounting the heatsink and cirquit in the chassis....

It's allways safer to use TF package.

I am not following you...
I seems that my third LM went in heaven. Yesterday I bought new one and just slowly raise voltage to 5 V and there was again dc on output! After reading your post I cheched LM's chassis voltage and in all three of them there was Vee on them and therefore on heatsinks.
I just cant understand what happened! If there were some design problems the circuit wouldn't run the first time. I haven't any broken pins. How there can be isolation between heatsink and chassis? Up is conductive part and down in nonconductive. I put heatsink on conductive part and it worked like that in saturay and days ago when I was soldering separate monoblocks.