second aleph3 not working!

cowanrg · 18th August 2004, 07:45 PM

so, after a LOT of headache from the first aleph3, i got the second chassis built, and its not working!

its the same design (an exact replica) of the one seen at my site

http://www.cowanrg.mesanetworks.net/projects/

and in this thread:

aleph3 built, but humming...

ive done some minor testing as of now. i was blowing fuses, and im still not sure why. i took the power supply apart, then put it back together, and that's fixed.

i accidentally had Q106 and Q107 wired backwards, that is now fixed.

right now, the power supply is good. im getting a nice +-26.66V from the caps. however, im getting almost no draw from the amp. i think i measured the + rail at 0.025A at idle. way too low. my other amp draws 1.88A (its an RMS meter, so that is right on).

the LED doesn't even come on, the fets dont get hot. i have yet to make any board measurements, but with the draw so low, i dont know if it would tell me anything... the only thing i can really tell about the board is that Q103 is getting hot. i left it on for a little bit, and it was quite warm, and everything else was cold.

any simple ideas? if not, ill just have to take it all apart

Netlist · 18th August 2004, 07:55 PM

What's the voltage across R108, R106 and CE Q105?

/Hugo

cowanrg · 18th August 2004, 07:59 PM

i should add that the LED isnt coming on either. i didnt think that was important, but looking at the schematic, it appears like it could.

Netlist · 18th August 2004, 08:06 PM

Quote:

Originally posted by cowanrg
the LED doesn't even come on(

Quote:

Originally posted by cowanrg
i should add that the LED isnt coming on either.

You did..

Time to get some sleep?

/Hugo

cowanrg · 18th August 2004, 08:08 PM

hah, duh.

its my day off. my brain doesnt like to work on my day off.

eLarson · 18th August 2004, 08:31 PM

Are there any pins shorted together (Gate to Source, say) such that MOSFETs won't be able to turn on?

cowanrg · 18th August 2004, 08:33 PM

pins shorted on the actual fets you mean? i can check.

cowanrg · 18th August 2004, 11:56 PM

wow, i got some really neat readings...

first off, i followed Mike's advice and tested this amp against the working one.

to answer eLarson first, i am not getting any shorts on the fets. they seem ok i guess.

MikeW told me to measure voltage across Q101, Q102, and Q103. here is what i got on my first amp: 3.6, 3.5, and 3.5. a little low, but fine i guess. on the bad amp i get: 3.3, 52, 26.

(on the second transistor, reading on G was ~26v, and on S was -26v, so summed at 52v. on the third, it was 0v on G, and -26v on S).

so, there is definately something wrong there. do i replace Q102 and Q103? or is something else causing the error?

cowanrg · 19th August 2004, 12:15 AM

wow.

i measured some resistors. across R108, R106, and Q105. all measurements were nothing! i got a 0v drop across them.

SO, power just isnt getting in. however, im measuring a 0.024A draw across the negative rail. so, power IS connected right, the caps are charging, so i would assume the power supply is ok. (i made measurements at each bridge, and each rail, all are fine).

oh, and i get ~26v or so at the component, so power is running through the board.

moe29 · 19th August 2004, 12:16 AM

Looks like you are getting rail voltage on your FETS.

Your 3watt resistors probably got burned. Thus probably taking
out their corisponding FETS.

Yank 1 of the fets and test it to see if it's still good.

If it's bad you gotta find out why that happened.

Maybe a bad solder.

Replace the FETS and R's and try again.

just my quick thoughts.

18th August 2004, 07:45 PM	#1
cowanrg diyAudio Member Join Date: Apr 2002 Location: Lafayette, CO	second aleph3 not working! so, after a LOT of headache from the first aleph3, i got the second chassis built, and its not working! its the same design (an exact replica) of the one seen at my site http://www.cowanrg.mesanetworks.net/projects/ and in this thread: aleph3 built, but humming... ive done some minor testing as of now. i was blowing fuses, and im still not sure why. i took the power supply apart, then put it back together, and that's fixed. i accidentally had Q106 and Q107 wired backwards, that is now fixed. right now, the power supply is good. im getting a nice +-26.66V from the caps. however, im getting almost no draw from the amp. i think i measured the + rail at 0.025A at idle. way too low. my other amp draws 1.88A (its an RMS meter, so that is right on). the LED doesn't even come on, the fets dont get hot. i have yet to make any board measurements, but with the draw so low, i dont know if it would tell me anything... the only thing i can really tell about the board is that Q103 is getting hot. i left it on for a little bit, and it was quite warm, and everything else was cold. any simple ideas? if not, ill just have to take it all apart

18th August 2004, 08:31 PM	#6
eLarson diyAudio Member Join Date: Aug 2002 Location: Gaithersburg, MD	Are there any pins shorted together (Gate to Source, say) such that MOSFETs won't be able to turn on? __________________ Would a woodchuck bother to chuck MDF?

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18th August 2004, 07:55 PM	#2
Netlist diyAudio Moderator Join Date: Jan 2003	What's the voltage across R108, R106 and CE Q105? /Hugo

18th August 2004, 07:59 PM	#3
cowanrg diyAudio Member Join Date: Apr 2002 Location: Lafayette, CO	i should add that the LED isnt coming on either. i didnt think that was important, but looking at the schematic, it appears like it could.

18th August 2004, 08:08 PM	#5
cowanrg diyAudio Member Join Date: Apr 2002 Location: Lafayette, CO	hah, duh. its my day off. my brain doesnt like to work on my day off.

18th August 2004, 08:33 PM	#7
cowanrg diyAudio Member Join Date: Apr 2002 Location: Lafayette, CO	pins shorted on the actual fets you mean? i can check.

18th August 2004, 11:56 PM	#8
cowanrg diyAudio Member Join Date: Apr 2002 Location: Lafayette, CO	wow, i got some really neat readings... first off, i followed Mike's advice and tested this amp against the working one. to answer eLarson first, i am not getting any shorts on the fets. they seem ok i guess. MikeW told me to measure voltage across Q101, Q102, and Q103. here is what i got on my first amp: 3.6, 3.5, and 3.5. a little low, but fine i guess. on the bad amp i get: 3.3, 52, 26. (on the second transistor, reading on G was ~26v, and on S was -26v, so summed at 52v. on the third, it was 0v on G, and -26v on S). so, there is definately something wrong there. do i replace Q102 and Q103? or is something else causing the error?

19th August 2004, 12:15 AM	#9
cowanrg diyAudio Member Join Date: Apr 2002 Location: Lafayette, CO	wow. i measured some resistors. across R108, R106, and Q105. all measurements were nothing! i got a 0v drop across them. SO, power just isnt getting in. however, im measuring a 0.024A draw across the negative rail. so, power IS connected right, the caps are charging, so i would assume the power supply is ok. (i made measurements at each bridge, and each rail, all are fine). oh, and i get ~26v or so at the component, so power is running through the board.

19th August 2004, 12:16 AM	#10
moe29 diyAudio Member Join Date: Dec 2002 Location: Florida	Looks like you are getting rail voltage on your FETS. Your 3watt resistors probably got burned. Thus probably taking out their corisponding FETS. Yank 1 of the fets and test it to see if it's still good. If it's bad you gotta find out why that happened. Maybe a bad solder. Replace the FETS and R's and try again. just my quick thoughts.

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