UCD400 and speaker fried - why?? - Page 2 - diyAudio
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Old 31st October 2006, 05:27 PM   #11
eleson is offline eleson  Sweden
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Quote:
Originally posted by madstamm
hm, that sound unreasonable in my case - there's no chance that a short could have occurred..

I *did* have the modules sitting on the ESD pads that they shipped with. A flukemeter measures them at 10+MOhm though with the meter pins 5mm apart... couldnt imagine..

other ideas?

I know I've seen Jan-Peter mention that the protective foam should be removed, because it could/would result in broken units.
/Erland
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Old 1st November 2006, 03:33 AM   #12
-CGL- is offline -CGL-  Finland
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Quote:
Originally posted by madstamm
hm, that sound unreasonable in my case - there's no chance that a short could have occurred..

I *did* have the modules sitting on the ESD pads that they shipped with. A flukemeter measures them at 10+MOhm though with the meter pins 5mm apart... couldnt imagine..

other ideas?
http://www.diyaudio.com/forums/showt...116#post939116
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Old 1st November 2006, 07:50 AM   #13
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thanks for the info regarding ESD modules. I will try to get info from hypex about this issue. Still seems strange to me that it could lead to problems... maybe the ESD pads start to get really conductive at 400kHz??

This is the response I got from Hypex regarding overheating, by the way:

"Overheating could be the case. That is the reason why the manual says you should provide for additional cooling."

...which is pretty much useless... "could" means next to nothing if you ask me...?
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Old 1st November 2006, 08:24 AM   #14
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thanks for the info regarding ESD modules. I will try to get info from hypex about this issue. Still seems strange to me that it could lead to problems... maybe the ESD pads start to get really conductive at 400kHz??

This is the response I got from Hypex regarding overheating, by the way:

"Overheating could be the case. That is the reason why the manual says you should provide for additional cooling."

...which is pretty much useless... "could" means next to nothing if you ask me...?

Quote:
Originally posted by gl
Hi madstamm,

I would suspect one of two things: 1) a wiring error (I know you'll swear it isn't so, but that's what usually happens to me), or 2) it's a grounding problem. It's easy to get ground loops with two channels being run off one supply.

...
Hi Graeme,

I connected my amps like this:

Click the image to open in full size.

I did not earth any part of the test-setup, meaning the secondary side was left floating. Looking back this might not have been a good idea:

could not earthing the secondary "0V" net result in a large potential difference between signal and power ground in the amplifier? Or are signal and power grounds in the hypex modules DC-connected at some point?

thanks again for info so far.

mike
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Old 1st November 2006, 09:09 AM   #15
Jorrit is offline Jorrit  Netherlands
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Quote:
Originally posted by madstamm
thanks for the info regarding ESD modules. I will try to get info from hypex about this issue. Still seems strange to me that it could lead to problems... maybe the ESD pads start to get really conductive at 400kHz??

This is the response I got from Hypex regarding overheating, by the way:

"Overheating could be the case. That is the reason why the manual says you should provide for additional cooling."

...which is pretty much useless... "could" means next to nothing if you ask me...?

Hi Madstamm,

You could have saved yourself and other people here a lot of trouble just by reading the manual for instance. Just a few lines from the manual:
"...Altough Hypex UcD modules are based on very efficient Class-D technology, additional cooling is a MUST." The label (the big yellow one with the exclamation mark and starting off with 'Caution!') that holds the antistatic bag together says: "...Protection foam is for transportation purposes only. Remove foam before use."
Which part of these phrases are so hard to understand? The manual wasn't written in french now was it?
Maybe you should read the manual before firing things up and have a bit more patience than a kid unwrapping his gifts on christmas eve.

Cheers,
Jorrit
Hypex Electronics
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Old 1st November 2006, 09:38 AM   #16
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Mr Mozes,

Im sorry to have riled you up - I said at the beginnning of the posts that I realize that I made a mistake. I assumed and the asumption was wrong. I now also realize I didnt read the big yellow label, Im tendentially interested in the present more than the package... and YES, unpacking a neat amp IS like unpacking xmas gifts, would not be good if it was otherwise
Normally the yellow label warns of ESD susceptibility only, so this is what i assumed it to say.

Please do not confuse these posts as an accusation. Im trying to find out WHY the amp broke and WHAT parts might all be affected, not trying to claim a poor product. In contrary, I was very well pleased, for 10min at least

I still do not have an answer to my questions:
1. Are melted output transistors a typical thermal failure
2. What other parts might be in trouble

YOU might save yourself a lot of trouble by thoroughly reading posts (and eMails) as well.

cheers,

Mike
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Old 1st November 2006, 11:12 AM   #17
Pafi is offline Pafi  Hungary
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BWRX!

Quote:
They shouldn't blow up if you're running them at lower power levels without a heat sink.
This was a UCD400! It has a significant idle loss, ~8 W as I remember, and this power on such a small surface causes a very high temperature without forced cooling (could be >150 C). Failure was a quite normal consequence.

madstamm!

Quote:
"Overheating could be the case. That is the reason why the manual says you should provide for additional cooling."
...which is pretty much useless... "could" means next to nothing if you ask me...?
You can't expect more. They haven't seen your config, so possible alternative reasons of failure cannot be eliminated.
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Old 1st November 2006, 12:03 PM   #18
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Quote:
Originally posted by Pafi
BWRX!

This was a UCD400! It has a significant idle loss, ~8 W as I remember, and this power on such a small surface causes a very high temperature without forced cooling (could be >150 C). Failure was a quite normal consequence.

madstamm!

You can't expect more. They haven't seen your config, so possible alternative reasons of failure cannot be eliminated.
I reacted because I asked 2 questions and got an overly short response to only one of them. I suppose this is unprofessional conduct on my part, I apologize.

I had the modules running with 24V in the lab the day before "the experiment", and they got only handwarm during several hours of ON-time. (by the way, this was with the esd pads ON) In the flight of anticipation I disregarded the consequence of doubling the voltage rails (quadrupling the power). The ESD pads were attached during the hours of ON-time in the lab by the way! NOt like Id recommend this, but I think that means in my case ESD pads were probably not the cause of failure.

Im not sure about the 8W melting the output FETs by the way. I'd guess 10/W heatsink-ambient resistance of the UCD400 heatsink, given still air (very little convection cooling, mostly radiation). This gives (very roughly) 100 heatsink temp, and probably not more than 125 die temp. the datasheet specs operating temp up to 175.

At die=125:
max current = 20A
Ron = 1.8x normal value... hmmm this one might do it!

okok, the rising Ron probably killed the FETs. Power dissipation would increase ~proportionally with Ron, which in turn would increase temp again, and so on.
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Old 1st November 2006, 03:30 PM   #19
RX5 is offline RX5  Philippines
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Default Re: UCD400 and speaker fried - why??

Quote:
Originally posted by madstamm
because the ESD pad i left the amp on had a melted imprint of the 5mOhm shunt resistor... this could also be from current AFTER the FET shorted though.

I suspect the amps got too hot, after running them without cooling surface.

this might help....uhhhmmm you say you put the modules under an ESD pad?? arent ESD pad/s conductive??? pls test it with an ohmeter.... if it played, and ONLY at low volume settings, I believe you have caused some -shorts- by way of THAT pad...

-OR-

have you been playing with the deadtime trimpot?
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Old 1st November 2006, 04:16 PM   #20
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ESD pads are conductive, just like any almost other material... but their conduction/resistance is controlled. In post 8 i mentioned "measuring" (if one could call it that the pad. I used two pointy ohmmeter probes and got ~10MegOhm with the tips 5mm apart.

i also ran the modules on the pads for a few hours w/o anything happening. (at low supply voltages)

Im quite sure now that it was in fact the output transistors getting too hot - i did a quick calc and it looks like running the modules w/o an additional heatsink and without any forced cooling generates enough heat to increase the fet temperature, effecting some important parameters adversely. the degrading of the parameters in turn generates more heat, this degrades the fet more, etc etc... runaway thermal bomb, with the clock quite possibly being at 10min.

so idling the modules at recommended PSU voltages will likely kill them. not exactly sure, depends a little on just how good the heatsink radiates...

and no playing with any pots maybe later
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