Power supply in HP Deskjet 890C

[Guest]

Archived from groups: comp.periphs.printers (More info?)

Hi

the power supply in 890 C is base on UC3842, then i measure on Vcc
(pin 7) the voltage is rising slowly, is take minutes to rise 16 V,
where the PSU start the output of the power is 19 V and the 2 LED
lights up in few seconds, after that the power supply turn off and the
Voltage on UC3842 pin 7 starts to increase slowly again.

What can be wrong?

 

[James]

Archived from groups: comp.periphs.printers (More info?)

look for a small leaky capacitor
something like 1µF

"arne" <bravnborg@mobilixnet.dk> schreef in bericht
news:4e988155.0410250152.221bd26c@posting.google.com...
> Hi
>
> the power supply in 890 C is base on UC3842, then i measure on Vcc
> (pin 7) the voltage is rising slowly, is take minutes to rise 16 V,
> where the PSU start the output of the power is 19 V and the 2 LED
> lights up in few seconds, after that the power supply turn off and the
> Voltage on UC3842 pin 7 starts to increase slowly again.
>
> What can be wrong?

 

[luchenbe]

A 470 k resistor in the power supply developped an open circuit. It's likely used to pre-power the unit so that it can accept commands from the 2 buttons ...