Aleph 30 problem - half of power supply voltage on speakers output - diyAudio
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Old 14th March 2009, 08:00 PM   #1
yoke is online now yoke  Croatia
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Default Aleph 30 problem - half of power supply voltage on speakers output

Hi all
I believe that someone before me have this kind of problem but the search option didn't come up with result.

I manage to burn one chanell of Aleph30 ;-)

So does any one have some idea what could cose that I have half of power supply voltage on speakers output ?
When I measure voltage on source resistors ( 0.5/5W) on side with Q9/Q11/Q13 I have 0.45V but on the other side I have around 0.1V across source resistors resistors.

What should I check ?

Thanks

(p.s. I'm not an expert, this is my hoby and I only have one multimeter ;-))
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Old 15th March 2009, 04:52 AM   #2
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I've got two meters, and managed to let out plenty of the magic smoke. Looking at the A30 service manual, I don't see any Q13. Which schematic are you using? Maybe a close up pic if possible.

-john
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Old 15th March 2009, 05:24 AM   #3
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first check output mosfets for shorts

desolder suspicious ones and retest , when you find malfunctioning half (lower or upper)
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Old 15th March 2009, 07:20 AM   #4
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Quote:
Originally posted by MEGA-amp
I've got two meters, and managed to let out plenty of the magic smoke. Looking at the A30 service manual, I don't see any Q13. Which schematic are you using? Maybe a close up pic if possible.

-john
sorry for misunderstanding.
I was reading from PCB markings so I state Q13 and so. The PCB that I'm using is from BrianGT GB and there was shematic with it but I have reinstall windows and didn't have time to transfer old files on new one, so at this moment I don't have original shematic for those PCB.
A friend diyer have send me original Alwph30 service manual and the mosfets that I'm talking about are Q6-Q8

Could someone please send me shematic that have come with Brians Mini and Aleph 30 PCB since there is difference in markings betwin original and Brians.
And it's hard for me to track diferences by looking on PCB

(email josip.katalinic at gmail.com)

Thanks
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Old 15th March 2009, 07:23 AM   #5
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Quote:
Originally posted by Zen Mod
first check output mosfets for shorts

desolder suspicious ones and retest , when you find malfunctioning half (lower or upper)

Is it posibile to check output mosfets while thay are solder ?
couse I have chack them and they all mesure the sime...
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Old 15th March 2009, 08:55 AM   #6
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it seams that Brian's schematic is close to the original;
I have masure voltage over
- R11 - 5V - o.k.
- Q3 Dpin to 0 - 4V o.k
- Q5 - 4.5V - I think o.k.
- R14 - I have 3.1V not o.k.

and I have notice something strange at least visualy...bacause I don't think that I solder this bad ;-) but the PCB under Capacitor ( I think it's C11 ) looks burned ?

not shure is C1 on this pcb the C11 on original shematic ?
http://www.diyaudio.com/forums/showt...816#post585816
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Old 15th March 2009, 09:00 AM   #7
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Here it is again with red cloud ;-)

one more thing...
this amp was working fine, for some time, until I conect wrong output of 7.1 preamp (NAD S170) to onother amp which couse one Alpeh 30 amp to make some duuulllll/tuuull sound and after couple sec it start to smell bad ;-)

I don't know how conecting wrong preamp output to other amp can make some amp which is conected to another output to burn ? but !
...complicated story...it would be much easyer to draw it then to describe it with words...

(sorry for bad english)
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Old 15th March 2009, 11:40 AM   #8
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OK - seems that you have problems with biasing of output , not with burned output mosfets

check zenners for short , especially one in input CCS ( 9V1)

I'll send you Algar_emi's A30 pdf , with all measuring points , so you can compare ... and write here what's difference
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Old 15th March 2009, 12:15 PM   #9
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Quote:
Originally posted by Zen Mod
OK - seems that you have problems with biasing of output , not with burned output mosfets

check zenners for short , especially one in input CCS ( 9V1)

I'll send you Algar_emi's A30 pdf , with all measuring points , so you can compare ... and write here what's difference

I have recive pdf ... thanks Choky ;-)
will play a litlle and post results...
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Old 15th March 2009, 02:11 PM   #10
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For now...
Colegue diyer advised me to mesure voltage on ZTX base.

I have conect one side of multimeter to the ground and with the other I mesure voltage on Q4 base which is like 21V and on the Q5 is like 13V.

( I mesured resistance betwin ZTX leegs , they are not shorted so I think thay are not broken )
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