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. The problem is in the first capacitor, I
replaced it again with a new 105 deg type and it works but I notice
the capacitor gets very hot in just 10 minutes. All the capacitors in
the supply check fine on the ESR meter. Tried different brands of
capacitors and the ones having the smallest ESR work better but also
get very hot.

It seems to me this receiver is too exigent on the quality and ESR of
this capacitor. Do you think this is normal and I should be looking
for a really good capacitor or should I look for another problem
elsewhere? Could I do something to reduce the stress it is put on?

The waveform on this capacitor looks like a sawtooth, rises really
fast and falls slowly until half cycle, then remains constant for the
remaining half cycle. Amplitude around 0,4Vpp to 1Vpp depending on the
capacitor used.
What brand and series of "low ESR high quality 105 deg replacement"
did you use? I would recommecd using a Panasonic FM series or
equivalent ultra-low ESR high quality ca fron Nochicon, UCC, or
Rubycon for something like this.

PlainBill