On Sun, 30 May 2010 17:45:24 -0500, "David" wrote:



wrote in message
.. .
On Sun, 30 May 2010 04:45:45 -0700 (PDT), Jeroni Paul
wrote:

I'm repairing a DTV decoder Saivod DT2012 (chip Cheertek
and tuner LG)
that had a swollen capacitor in the power supply. 6 months
ago I
already replaced this capacitor with a low ESR high
quality 105 deg
replacement but it just lasted 6 months and is swollen
again.

The capacitor is EC205 1000uF 16V and is the filter for 5V
output in a
switching power supply. Typical design, small transformer,
rectifier
diode, first capacitor, inductor and second capacitor with
TNY265 as
primary controller chip. The second capacitor remains cold
and checks
fine on the ESR meter.

Unless this is a flyback type supply, a typical forward
switching power supply design does not have a large
capacitor on the output of the rectifier. The rectifier
diodes go directly to an inductor with the main filter
capacitor connected to the output of the inductor. If it a
flyback design, you could try putting a 1 uf or so ceramic
capacitor across the larger capacitor. Using a high voltage
replacement is not a good idea since the higher the voltage
rating, the higher the ESR.

Since when? Quick check for 1000/25 and 1000/35 Panasonic caps
show ESR goes from .033 down to .025 for higher volt rating.

Grant.
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