lexicon pcm-xx power supply repair

[Audioman]

@Khron
modification with battery holder and CR2032 done

 

[rob61]

I have a PCM-70 (original owner) and I'm getting a "battery low" error when I turn it on. Is the battery soldered in? Are replacements still available?

 

[transient]

Re the PCM70 battery it's yes on both counts. For example:

https://analogclassics.com/product/lexicon-pcm70-battery/

 

[Audioman]

Di solito è contrassegnato su un lato, ma considerando che non è una cosa ad alta potenza, qualcosa come uno da 10 ohm di diametro simile dovrebbe andare bene.

https://en.wikipedia.org/wiki/Thermistor#NTC
(Secondo punto elenco in quella lista)

@Khron I measured the thermistor with the transistor tester and it gave me the value of 12.7 ohms (attached photo), the one I bought is 5 ohms could it be a problem?

 

[Khron]

It's not that critical, and it's a pretty low-power device anyway.

 

[Audioman]

Non è così critico, ed è comunque un dispositivo piuttosto a basso consumo.

@Khron I found one with smaller body size but ohm value closer to stock one, can i use this?

 

[Khron]

I'd rather stick with the physically bigger one.

 

[hildy]

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 :-/

Hi. Was just dropping by and saw your post. We just repaired one of these at my shop. Why not save your solder and just drop in a new PSU:

https://www.mouser.com/ProductDetail/709-PT45C709-PT45C
Mfr. #:
PT-45C