UCD400 and speaker fried - why??

[madstamm]

I recently bought two UCD400 modules. Have the parts for a dual mono setup, but I hooked the two modules up to one supply for testing yesterday.

The modules are the "standard" version, NO MODS, so the inputs are AC coupled. (single ended)

I ran the modules WITHOUT heatsinks for about 10min, at relatively low listening levels. After this time, (I was in the kitchen) I heard a very loud **POP** - I ran to the living room, heard the right speaker still playing and saw the left diaphagm looking to pop out of the chassis.

I ran for the power cord, but didnt make it in time, the speaker fried first

I disconnected the blown speaker and repowered the amps. The amp LEDs still work, and the "right" amp/speaker combo sounds fine.

The right amp's heatsink gets warm, the left heatsink stays cold. However, I know that the modules get warm without Load, so I was a bit suspicious at this point.

Later I hooked up the working speaker (have no instrumentation at home) to the left amp.
The speaker outputs were apparently at PSU voltage, because the resulting pop and spark was quite energetic.

The drive transistor(s) are in fact shorted out. (Am at work now, have access to all necessary equipment) The amp must have gotten very hot, 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.

Anyone with tips or experience? Is it reasonable to just replace the transitors or should I expect other problems? The MOS-drive transistor measures fine...

Thanks,

Mike

PSU:
Trafo: 40Vsec, 500VA
Caps: 2x Epcos Sikorel 10mF, bypassed w 100nF film
Dual rectifiers
Unloaded Voltage = ±55.4V

Load:
8ohm CSS FR125 10cm Fullrange, 7L sealed.

[madstamm]

also, what are opinions on replacing the FDP42AN15A0 with an different part, possibly with lower RDSon?

How tolerant is the UCD drive circuit on drive transitor parameters such as gate charge?

Would the developers care to drop a line?

thanks,
mike

[ghemink]

Originally posted by madstamm
also, what are opinions on replacing the FDP42AN15A0 with an different part, possibly with lower RDSon?

How tolerant is the UCD drive circuit on drive transitor parameters such as gate charge?

Would the developers care to drop a line?

thanks,
mike

You could contact Hypex directly, in my experience they are very responsive. It is indeed a no-go to use the modules without any heatsinking. They do not need much but they do need some.

Best regards

Gertjan

[mitch90]

Hello madstamm.

Sorry to hear about your speaker.
As far as I know UCD gate drivers are
matched with MOSFET they drive.
Best approach would be to use same device
'FDP42AN15A0' as replacement.

Regards,


MITCH.

[lucpes]

Originally posted by madstamm

I ran the modules WITHOUT heatsinks for about 10min, at relatively low listening levels. After this time, (I was in the kitchen) I heard a very loud **POP** - I ran to the living room, heard the right speaker still playing and saw the left diaphagm looking to pop out of the chassis.

I know, the speakers you used do not draw much power, but I have noticed that hypex says DO NOT run the modules without a heatsink...

[madstamm]

I realize of course that I was not "supposed" to run the modules w/o heatsinking -

it is not a question if I have done the right thing or not, I certainly havent

I am curious if running w/o a heatsink will *typically* cause the output transistors to "melt" or not, and if I should be concerned that other parts have been destroyed as well.

again, i would think that hypex has some experience in thermally destoying their modules, (i did write them an eMail a few min ago), but has anyone else cratered their amps?

[BWRX]

They shouldn't blow up if you're running them at lower power levels without a heat sink.

Something else probably happened, especially since your other amp still works fine.

I fried one of my 180 modules due to what I believe was a short from output to ground right at the fast on terminals. I checked some parts and fried more than just the output fets.

[Pierre]

Aren't UcD modules protected against output shortcircuit?

[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?

[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.

I've seen both of these cause huge problems when first turning on new amps of all types. I have to admit though, I haven't heard many stories about new amps frying speakers.

Good luck with this.

Graeme