DTV decoder repair, capacitor gets too hot
in [Repair]
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From: Jeroni Paul on 30 May 2010 07:45 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.
From: PlainBill47 on 30 May 2010 14:06 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. 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
From: Grant on 30 May 2010 17:36 On Sun, 30 May 2010 11:06:28 -0700, PlainBill47(a)yahoo.com wrote: >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. 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. Up the cap's voltage rating too, if a bigger cap will fit in the box. Grant. -- http://bugs.id.au/
From: David on 30 May 2010 18:45 <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
From: Grant on 30 May 2010 20:12
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. 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. -- http://bugs.id.au/ |