On 6 Jul 2004 19:28:18 GMT, BigBadger put
finger to keyboard and composed:

Hi,
I've been given a friends PC Power supply to repair. It's a Enermax EG651
(550W) model. It was damaged when he plugged it into a 240V supply while
the voltage select switch was on 115V (Doh!!).

Anyway a quick visual shows that two large ceramic capacitors are blown.
The capacitors are mounted next to where the wire from the voltage select
switch joiuns the pcb. They are marked Z1 and Z2 on the pcb and TVR 10241
on the components themselves, they are about 10mm diameter.

Does anyone know what rating these are?

Also if anyone knows what further damege may have been done (hopefully none
)

These two disc shaped components are MOVs (metal oxide varistors) with
a breakdown voltage of 240V (?). I'm betting they are connected across
each of the two main filter capacitors. In normal operation each of
these caps charges to around 175VDC. If the SMPS is wired for 110V
when connected to a 240VAC supply, then these caps will attempt to
charge to 350VDC. The MOVs prevent this from happening ...
catastrophically and sacrificially. If you are lucky, only an
additional fuse and NTC resistor may need changing. It may be a good
idea to remove the voltage selector switch and its two wires if you
intend to operate the PSU solely from a 240VAC supply. This switch is
open in 240V mode. You can also leave out the MOVs in this case, or
replace them with two high value resistors, eg 220K 0.5W, if not
already present.


- Franc Zabkar
--
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