Hafler 500 DC Offset 27 Volts!

[rudes]

I just replaced my old driver boards that did NOT have the DC offset adjustment. I replaced them with newer stock ones that has the adjustment. DC offset is so high in both channels and adjustment pot does nothing. Obviously something not right, but everything is new!

Also why does the relay click on with this amount of offset?

 

[Binkman]

Greetings;
schematic in owners manual.. believe there is a service manual online, too.
https://www.hifiengine.com/manual_library/hafler/dh-500.shtml
This may help on dc offset.. (the issue of protection circuit is another issue that can be researched.)
https://audiokarma.org/forums/index.php?threads/dc-offset-adjustment-on-a-hafler-dh-500.142396/
I'm sure others will post.

 

[rudes]

Thanks. I have all this info, but can't find a service manual. I never heard of DC offset so high, and why the relay does not detect it.

 

[loudnoises]

Thanks. I have all this info, but can't find a service manual. I never heard of DC offset so high, and why the relay does not detect it.

Obligatory check your meter range...

Aside from that, if the pot does nothing, are these really new? Or rebuilt? Check orientation of the components.

 

[spark1]

I just replaced my old driver boards that did NOT have the DC offset adjustment. I replaced them with newer stock ones that has the adjustment. DC offset is so high in both channels and adjustment pot does nothing. Obviously something not right, but everything is new!

Also why does the relay click on with this amount of offset?

It should not. Are you sure of your readings? Are you sure you are adjusting the correct VRs? More importantly, are you confident that the new boards were installed correctly, and with any necessary retrofits?

Did you turn the unit up o n a DBT after installing the new boards?

 

[rudes]

I purchased new blank boards and stuffed them with new parts. The bias pot works and I can adjust to 350ma. I have two meters and both read the same on the DC offset. As stated, the pot for the DC offset does nothing as well. Relay clicks on. I used a variac to turn it on.

 

[Skywatcher]

I just replaced my old driver boards that did NOT have the DC offset adjustment. I replaced them with newer stock ones that has the adjustment. DC offset is so high in both channels and adjustment pot does nothing. Obviously something not right, but everything is new!

Also why does the relay click on with this amount of offset?

Both fuses must be installed or you will get that voltage. Or something is wrong with the boards so recheck everything, especially transistor and diode orientation. I always use a DBT with a 150w bulb (to start) instead of a variac on these DH-500.