Aleph5 (MiniA) in flames

stighe · 22nd April 2008, 10:07 PM

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 · 23rd April 2008, 02:36 AM

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 · 23rd April 2008, 03:35 AM

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 · 23rd April 2008, 09:48 AM

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 · 24th April 2008, 07:07 PM

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 · 25th April 2008, 12:29 AM

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 · 25th April 2008, 12:41 AM

Quote:

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 · 25th April 2008, 07:53 AM

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 · 25th April 2008, 09:02 AM

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 · 25th April 2008, 11:00 PM

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

22nd April 2008, 10:07 PM	#1
stighe diyAudio Member Join Date: Nov 2007	Aleph5 (MiniA) in flames 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

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23rd April 2008, 02:36 AM	#2
gni diyAudio Member Join Date: Sep 2006	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. . .

23rd April 2008, 03:35 AM	#3
Nelson Pass The one and only Join Date: Mar 2001	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.

23rd April 2008, 09:48 AM	#4
Tarasque diyAudio Member Join Date: Dec 2002 Location: Netherlands	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...

24th April 2008, 07:07 PM	#5
folkeb diyAudio Member Join Date: Jan 2006 Location: Trondheim	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

25th April 2008, 12:29 AM	#6
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	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

25th April 2008, 07:53 AM	#8
Tarasque diyAudio Member Join Date: Dec 2002 Location: Netherlands	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.

25th April 2008, 09:02 AM	#9
folkeb diyAudio Member Join Date: Jan 2006 Location: Trondheim	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...

25th April 2008, 11:00 PM	#10
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	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

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