Aleph5 (MiniA) in flames

[stighe]

Hi

I'm building an Aleph5 (miniA-PCBs). I connected one channel only to test and actually everything worked fine for about 3 minutes.

Then something strange happened!

Music stopped and two resistors caught fire. First R29 on one of the output boards, then R21 on the Amplifier board.

I have checked every wire, but everything seems fine. There's no visible damage to the other components on the cards.

Please see http://www.diyamps.com/aleph for PCB layouts and schematics.

Thank you

 

[gni]

Had problem using the supplied link to the schematic.

Sounds almost like thermal runaway. . .Class A
except the mosfet has a reverse thermal coefficient.


A bad solder joint.

There will be better answers. . .

 

[Nelson Pass]

The occasional flame is part of the game,

but the Alephs are not known for runaway bias, the DC value
being locked by a PN junction voltage.

 

[Tarasque]

I would check the insulation from the output devices to the heatsink. I've had similar problem what metal dust from drilling mounting holes was piercing the insulator pads, connecting the upper and the lower fet banks.

I have to say...A spectacular event when these power fets explode...

 

[folkeb]

What would you suggest be the best way of figuring out this rather explosive incident. We really thought that everything was working rather well, and then suddenly a thump in the speaker and then flames. First from the negative board on the heatsink, a 221 ohm resistor, then another 221ohm resistor on the main board.

Would you try hooking up the other channel (only using the PS)?

This incident sort of drained any motivation..but we´ll get over it!

Thanks for any help!

- Folke

 

[woodturner-fran]

Would anyone have links that work to the brianGT schematic and part list for the mini A?



I have the threads bookmarked but I haven't been able to access the diyamps or chipamps site.

Fran

 

[mpmarino]

a 221 ohm resistor

without the schem it's tough to tell exactly what part toasted, but your indicating a 221r resistor indicates that a gate resistor maybe blew. I'd check the output device corresponding to that resistor for a short....

 

[Tarasque]

Hi Folke,

When the insulation is OK, I would check the thermal coupling to the heatsink. This phenomena can also happen when the junction reaches >150C temp.

A burnt gate resistor is one of the typical events when the fet has a thermal overload.

Before firing the 2nd channel, I would check all components on the PCB as well as the insulation and the thermal coupling of the output devices.

 

[folkeb]

As a matter of fact the heatsinks were rather warm after only a few minutes. Didn't check the temperature of the fets as we were busy putting out the fire...

 

[woodturner-fran]

I almost have my casework finished and will be doing some wiring soon! I hope i don't see smoke!!!

Was there ever a set of instructions/schematic etc for the brianGT boards?

Fran

 

[mpmarino]

....poked around on the hard drive. Is this the one?

 

[woodturner-fran]

Brilliant!!!!


thanks a million for that. I mean, i hope I don't need it but its great to have it!!!

owe you one!

Fran

 

[woodturner-fran]

And there were no flames when I fired it up tonight!!

now, enough thread jacking, sorry to sighe for the OT posts. Have you made any progress?




Fran

 

[stighe]

Yes, I connected the other channel yesterday and it played for 1 hour without any problems.

I think Tarasque is right, one of the output devices wasn't properly connnected to the heatsink resulting in thermal overload.

 

[Magura]

The simple way to confirm proper isolation to the heatsink, is to take your meter, and see if any of the legs has connection to the heatsink.


Magura