On 02 Aug 2005 08:59:36 -0400, Sam Goldwasser
put finger to keyboard and composed:

me writes:

I cannot find anywhere replacement capacitor (680 uF, 200V). Can I use
any other value for capacitance? I need two of them replaced
(identical), they are inside switching power supply, the biggest ones.

If you are running on 240VAC you could use a single 330uF 400V cap.


- Franc Zabkar

bad idea.

No necessarily. If running a dual voltage (120/240 VAC) power supply
on 240 VAC, the input circuit forms a bridge rectifier with its output
across the two main filter caps (in series). The quesiton is what happens
with the centertap. If it's not used for anything else, then this approach
can work, but you'd have to trace the input circuit completely to be
sure it won't simply release smoke.

In most PSUs that I've seen one could simply replace one of the two
caps with a single 400V type, link out the remaining one, and then
remove the two redundant wires going to the 240/120 selector switch.
Some designs may have MOVs in parallel with the caps, in which case
these should be removed.

By coincidence, yesterday I dismantled a Sony TV set which had a PSU
which was configurable for single or dual capacitors. The Australian
version of this set had a single 560uF 400V cap, and the other cap was
linked out. The PCB real estate allotted to the 400V cap was slightly
larger than for the 200V one.


- Franc Zabkar
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