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Old 31st July 2014, 02:11 PM   #1
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Default Rising DC Offset

Hi All,

I have a problem with my Aleph J. One channel is working fine. But for the other channel, the DC offset seems to rise infinitely. When it reaches about 300mV, I turned it off. It started from 65mV and after about 2-3 seconds, it begins to climb and in a few seconds later, it reaches 200-300mV. The rail supply is 48V and before connecting the board, it was 56V.

I am using 2sj109 and bc550 for Q3 and Q4.

Thanks.
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Last edited by pmchoong; 31st July 2014 at 02:15 PM.
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Old 31st July 2014, 02:20 PM   #2
biju55 is online now biju55  India
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where did you buy those 2sj109 ?
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Old 31st July 2014, 02:29 PM   #3
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what voltage do you measure across R7? leave the amp on until it temperature settles.
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Old 31st July 2014, 02:30 PM   #4
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Quote:
Originally Posted by biju55 View Post
where did you buy those 2sj109 ?
It was brought long ago. The other channel uses the same sj109 from the person I brought. I brought about 10 pieces from him. I have burned about 4 of them.
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Old 31st July 2014, 02:33 PM   #5
uli is offline uli  Austria
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the sj109 is likely not the fault. check all voltage Parameters in the ccs
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Old 31st July 2014, 02:46 PM   #6
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the sj109 is likely not the fault. check all voltage Parameters in the ccs
the dc rises too fast. i don't know if i have enough time to measure it.
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Old 31st July 2014, 02:53 PM   #7
Zen Mod is offline Zen Mod  Serbia
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reflow all solder joints

replace input CCS components

replace small BJT in Aleph CCS
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Old 31st July 2014, 03:11 PM   #8
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Originally Posted by pmchoong View Post
the dc rises too fast. i don't know if i have enough time to measure it.
running this without a load is the way to go. even offset near the rail voltage should not harm
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Old 31st July 2014, 03:14 PM   #9
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Originally Posted by Zen Mod View Post
reflow all solder joints

replace input CCS components

replace small BJT in Aleph CCS
I have replaced all Q2, Q3 and Q4. They are new. The only different is thatthay are BC550.
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Old 31st July 2014, 03:15 PM   #10
uli is offline uli  Austria
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start tracking down the fault BEFORE swapping parts which are likely ok ;-)
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