F6 dc offset issues

[fabrice63]

Hi everyone,

I need your help to understand what's going on !!!

My right channel is having an strong dc at the output , P1 has almost no effect on it ( from 18.28 V to 18.42 V )

here are some measurement :

6.2 v across Z1 and Z2

18.8 v dc across R7

18.20 V dc across R9

16 v dc across R3

0.515 v dc across R2 ,very stable and easy to set

0.592 v dc across R1

42.2 v dc between output and R2

16.5 v dc between R3 and output


R1 and R2 are 0.56 ohm

Q1 and Q2 are new , from Mouser

Main supply +24.1 v / -24.0 v

Noise supply 2.0 mv AC




.

 

[Zen Mod]

post exact schematic you're using

 

[fabrice63]

I use the store board , in stock mode , without any mods , other than zener 6.3 v .


some more measurements :

42.2 v dc between out and V-

- 5.8 v dc between out and V+

.

 

[alvinlim]

Q1 short?


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[Zen Mod]

write again voltages across R9 and R10

measure voltages across R11 and R12

 

[fabrice63]

17.0 v dc across R9

0.070 v dc across R10

0.194 v dc across R11

0.000 v dc across R12

R2 and R3 are hot , rated 5W

Q1 is new , the old one behave the same .


.

 

[Zen Mod]

4mA across gate resistor of Q1 means Q1 is Dodo

replace it

 

[fabrice63]

ok , I will change it , and let you know .

i forgot to say that R11 and R12 are 110 ohms , will it change anything ?


.

 

[fabrice63]

As you said Zen / Alvin , changing Q1 solve the problem .

my IRFP-240 were new Vishay's from Mouser , but new doesn't mean always good 🙄

thanks for your help , useful as usual 😉


.

 

[Zen Mod]

 

[alvinlim]

Happy that it worked! Cheers mate.


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