for all of you guys who had trouble with lexicon pcm-90/91/80/81
i bought a pcm-91 with a faulty power supply, needless to say for a small amount of money ;-)
thought this couldn't be so complicated to fix. i wasn't so easy in the end....
at first i noticed the hi voltage cap which has a bulge, it has a voltage about 270 V dc (main ac is 230 v here in germany, so it has to 310 or sth. like that).
so i changed it; wasn't so easy to get a replacement because the height of the 100µ/400V el-cap is only 2,5 cm. finally i found a replacement....
because of known problem with electrolytic caps and smps i changed all other el-caps to 105° low esr types with same or greater voltage (red dotted)
next change was the switching mos, a IRF830 which has a low resistance from one pin to another, don't ask me which one...
after that and some looking at the other components i thought the ps should be able to work now. unfortunately it doesn't....
there are 310 V dc at the bulk cap but it seems like the copper-circuit doesn't start :-(
i changed the 2 small driver transistors, no success
after few days break i checked the rectifier diodes at the output side which were ok
at last i measured every resistor and capacitor on the hi voltage / mains side.
i found the r2, a 750kOhm / 0,5W has no resistance.
after replacing this beast my lex awake to new life
i saved 50 bucks a new smps would cost from the german lex service ;-)
maybe this helps some of you guys with faulty lexicon device...
thanks a lot to svart for the tc wizard ps & general switch mode power supply thread!!!
now i have a tc power supply with a more complicated failure on the bench :-/
i bought a pcm-91 with a faulty power supply, needless to say for a small amount of money ;-)
thought this couldn't be so complicated to fix. i wasn't so easy in the end....
at first i noticed the hi voltage cap which has a bulge, it has a voltage about 270 V dc (main ac is 230 v here in germany, so it has to 310 or sth. like that).
so i changed it; wasn't so easy to get a replacement because the height of the 100µ/400V el-cap is only 2,5 cm. finally i found a replacement....
because of known problem with electrolytic caps and smps i changed all other el-caps to 105° low esr types with same or greater voltage (red dotted)
next change was the switching mos, a IRF830 which has a low resistance from one pin to another, don't ask me which one...
after that and some looking at the other components i thought the ps should be able to work now. unfortunately it doesn't....
there are 310 V dc at the bulk cap but it seems like the copper-circuit doesn't start :-(
i changed the 2 small driver transistors, no success
after few days break i checked the rectifier diodes at the output side which were ok
at last i measured every resistor and capacitor on the hi voltage / mains side.
i found the r2, a 750kOhm / 0,5W has no resistance.
after replacing this beast my lex awake to new life
i saved 50 bucks a new smps would cost from the german lex service ;-)
maybe this helps some of you guys with faulty lexicon device...
thanks a lot to svart for the tc wizard ps & general switch mode power supply thread!!!
now i have a tc power supply with a more complicated failure on the bench :-/