On 11/06/10 21:59, Steve Smith wrote:
> Phil:
> Check how the voltage regulation takes place... it could be either a tl431
> and an opto or it could be from the aux winding that feeds the chip... if
> the diode on the aux winding is poorly (open) this may cause the op voltage
> to exceed the PIV of the diode... and also check the snubber RC across the
> flyback fet... open circuit R is also a possibility.

It's a TL431 and an optoisolator (I've already replaced both of them). 
In failure mode, the +12V rail does seem a bit high -- around +20V by 
the time I get my meter across it.

There's a HER107 series diode on the Aux winding which appears to be 
used to power the TEA1522 (diode - resistor - capacitor to ground). The 
Aux winding also gets wired to the AUX pin on the 1522 via a 75k resistor.

-- 
Phil.
piclist@philpem.me.uk
http://www.philpem.me.uk/
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist