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Pumpkin preamp - ordered by Steen , official making thread
Pumpkin preamp - ordered by Steen , official making thread
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Old 2nd September 2011, 11:43 PM   #3031
Zen Mod is offline Zen Mod  Serbia
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Pumpkin preamp - ordered by Steen , official making thread
try to desolder one of them ( either Q6 or Q8 ) then measure

if bad measurement stays , desolder other one and repeat ;
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Old 3rd September 2011, 01:14 AM   #3032
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Will do

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Old 3rd September 2011, 05:52 PM   #3033
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I pulled both Q6 and Q8 - the negative rail remains at -19V

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Bob
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Old 3rd September 2011, 06:31 PM   #3034
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Pumpkin preamp - ordered by Steen , official making thread
now is tricky

it seems that you can exclude possible shortie on pcb , because you measured 10K from neg leg to gnd ;

so - reason must be that some part is conducting excessive current when power is applied .

do this : dismantle heatsink , power up and observe which of those 5 mosfets is excessively heating ; 4 of them must have similar temp , and Q10 must be (almost) cold ;

off course - for start you must be sure that you don't have some wrong resistor there

in any case - fiddle with diode meter here and there ( between pins of each transistor , same as between pins and gnd ) , comparing differences between working and non-working channel , and you'll localize what's wrong
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Old 3rd September 2011, 06:38 PM   #3035
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thanks Choky - will do
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Old 3rd September 2011, 06:49 PM   #3036
Nelson Pass is offline Nelson Pass  United States
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Pumpkin preamp - ordered by Steen , official making thread
We are honored to have you here, Bob.

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Old 3rd September 2011, 08:45 PM   #3037
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well - if Papa is honored , count that I'm double ......

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Old 3rd September 2011, 09:59 PM   #3038
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We are honored to have you here, Bob.

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I am trying
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Old 3rd September 2011, 10:02 PM   #3039
flocchini is offline flocchini  United States
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now is tricky

it seems that you can exclude possible shortie on pcb , because you measured 10K from neg leg to gnd ;

so - reason must be that some part is conducting excessive current when power is applied .

do this : dismantle heatsink , power up and observe which of those 5 mosfets is excessively heating ; 4 of them must have similar temp , and Q10 must be (almost) cold ;

off course - for start you must be sure that you don't have some wrong resistor there

in any case - fiddle with diode meter here and there ( between pins of each transistor , same as between pins and gnd ) , comparing differences between working and non-working channel , and you'll localize what's wrong
I was measuring resistance and found on the board that works
R5=R6 =16k measured across each in circuit and

on the board that doesn't R5=R6 =100k

????

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Old 3rd September 2011, 10:21 PM   #3040
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well - if Papa is honored , count that I'm double ......


thank you doubly
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