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From: b on 30 May 2010 20:50
On May 30, 12:45 pm, Jeroni Paul <JERONI.P...(a)terra.es> 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.

might be worth checking the current drawn, out of interest.
i've repaired dozens of these sort of boxes, many of which are the
same inside (MX Onda, AXIL, T Boston, Engel....) and using caps rated
at 25v in place of the 16v fitted usually keeps them working.
-B

From: Jamie on 30 May 2010 21:18
b wrote:
> On May 30, 12:45 pm, Jeroni Paul <JERONI.P...(a)terra.es> 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.
>
>
> might be worth checking the current drawn, out of interest.
> i've repaired dozens of these sort of boxes, many of which are the
> same inside (MX Onda, AXIL, T Boston, Engel....) and using caps rated
> at 25v in place of the 16v fitted usually keeps them working.
> -B
>
Also, you may want to check or replace the UF "ULTRA Fast" diode in that
circuit. I found some that developed a leak but not enough to short and
pass some AC through from the switcher.. This can not only heat the
diode but the Cap. A simple test is to perform a thermal test on the
diode.. It should only be warm at best..




From: stratus46 on 31 May 2010 11:22
On May 30, 4:45 am, Jeroni Paul <JERONI.P...(a)terra.es> 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.

Where I used to work they had Samsung DTV tuners that had a similar
issue. In that case we mounted the capacitor on its side to get it
farther away from the diode next to it that was the source of the
heat. You might look into the Nichicon HN series caps or possibly an
organic polymer cap. AFAIK the HN caps are the lowest (?) ESR of the
'lytics but the polymers are supposed to be even lower. Would a larger
value cap help here? What is the actual load current and what is the
frequency of the ripple?

G²
From: PlainBill47 on 31 May 2010 15:26
On Sun, 30 May 2010 17:45:24 -0500, "David" <someone(a)somewhere.com>
wrote:

>
>
><PlainBill47(a)yahoo.com> wrote in message
>news:gu95065uln9ebjd6ndmh5tge54a2mbu806(a)4ax.com...
>> On Sun, 30 May 2010 04:45:45 -0700 (PDT), Jeroni Paul
>> <JERONI.PAUL(a)terra.es> 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.
>
>David
>
I am always dubious about advice offered by someone who cannot
comprehend a simple text description. From the original post:

"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."

Looking up the datasheet for the TNY265 controller I see that it does
indeed suggest the circuit description described above.

Now the question is, are you a troll, or simply uneducated?

PlainBill
From: Franc Zabkar on 31 May 2010 21:35
On Mon, 31 May 2010 10:12:44 +1000, Grant <omg(a)grrr.id.au> put finger
to keyboard and composed:

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

I just tried a thought experiment, but it failed. :-(

Let's say we have four identical capacitors, each with capacitance C,
esr R, and voltage rating V.

If we connect them as follows, we would expect the equivalent
capacitor to have a capacitance C, esr R, and voltage rating 2V.

|| ||
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o---| |---o
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- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
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