Repairing a PVR power supply
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From: Philip Pemberton on 9 Jun 2010 16:36 Hi guys, Here's a new one for me... switchmode power supply repair. I've got a "Nichimen" PVR sitting on my workbench; apparently it "jus' plain stopped workin'". It appears to have been made by some Chinese OEM or other, possibly "Cosmic Digital Technology Co. Ltd." The power supply board carries the markings "CO-DPA118 Ver2.0 2002-12-13", and appears to have been used in a DVD player as well. Schematics are on the second-to-last page of this PDF: <http://www.curto-circuito.com/esquemas/DVD/Sanyo/DVD%20Sanyo%20Hd60% 20Mtk1379%20Mtk%201369%20Service%20Manual.pdf> Here's what I've found out thus far: - The SMPSU I have is missing the components for the -12V rail, and the "1085" 3.6V regulator. This appears to be "by design" and an act of cost- cutting on the part of the manufacturer (why include power rails that aren't used by the product?) - Power filtering and rectification is fine. I've got 330V over C9 (47uF 400V). It also seems to be storing its charge over power-down.. I forgot to discharge said capacitor and got a nice electrical burn for my trouble. - Powered up on the bench, U1 (TEA1522P) appears to be totally inactive, and its Vcc (between pins 1 and 2) seems to be dead too. Given that it depends on the transformer running before it gets Vcc (it has a separate winding all to itself), that isn't surprising. - Drain (TEA1522 pin 8) is at 330V. Source is at 0V. The internal transistor is thus switched off (there's a resistor between Drain and Vss, there should be *some* voltage there). - A few of the resistors are reading differently in-circuit -- specifically, R1 (next to the TEA1522), R7 (next to the transformer), R12 (near the TL431) and R13 (same place). I think my meter's (Fluke 25 3digit) getting confused by surrounding circuitry... Question is, where do I go from here? Obviously I'm going to desolder one leg of each of the "suspicious" resistors, but I'm left with three other possible suspects: TL431 shunt regulator PC817 optocoupler TEA1522 SMPSU controller I've already shotgunned all the electrolytics (except the 47uF main filter) on the grounds that they were made by several known bad-cap manufacturers (Capxon, JP and one or two others). It's now loaded with Matsushita-Panasonic parts. So we can call the capacitors "known good" :) My plan (after checking the resistors) is to solder some wires across the 5V output, then bring it up to 5V with an external current-limited PSU. That should allow me to test the TL431 (by increasing and decreasing the PSU voltage). Testing the optocoupler should be possible too, though I think I might need a second PSU or a 9V battery for that. Can anyone suggest some other things I could check? I'm calling this a startup issue at the moment, seeing as that's what's happening -- the SMPSU is failing to start up. Thanks, -- Phil. usenet10(a)philpem.me.uk http://www.philpem.me.uk/ If mail bounces, replace "10" with the last two digits of the current year
From: PlainBill47 on 9 Jun 2010 17:20 On 09 Jun 2010 20:36:54 GMT, Philip Pemberton <usenet10(a)philpem.me.uk> wrote: >Hi guys, >Here's a new one for me... switchmode power supply repair. > >I've got a "Nichimen" PVR sitting on my workbench; apparently it "jus' >plain stopped workin'". It appears to have been made by some Chinese OEM >or other, possibly "Cosmic Digital Technology Co. Ltd." > >The power supply board carries the markings "CO-DPA118 Ver2.0 >2002-12-13", and appears to have been used in a DVD player as well. >Schematics are on the second-to-last page of this PDF: > <http://www.curto-circuito.com/esquemas/DVD/Sanyo/DVD%20Sanyo%20Hd60% >20Mtk1379%20Mtk%201369%20Service%20Manual.pdf> > >Here's what I've found out thus far: > - The SMPSU I have is missing the components for the -12V rail, and the >"1085" 3.6V regulator. This appears to be "by design" and an act of cost- >cutting on the part of the manufacturer (why include power rails that >aren't used by the product?) > > - Power filtering and rectification is fine. I've got 330V over C9 (47uF >400V). It also seems to be storing its charge over power-down.. I forgot >to discharge said capacitor and got a nice electrical burn for my trouble. > > - Powered up on the bench, U1 (TEA1522P) appears to be totally >inactive, and its Vcc (between pins 1 and 2) seems to be dead too. Given >that it depends on the transformer running before it gets Vcc (it has a >separate winding all to itself), that isn't surprising. > > - Drain (TEA1522 pin 8) is at 330V. Source is at 0V. The internal >transistor is thus switched off (there's a resistor between Drain and Vss, >there should be *some* voltage there). > > - A few of the resistors are reading differently in-circuit -- >specifically, R1 (next to the TEA1522), R7 (next to the transformer), R12 >(near the TL431) and R13 (same place). I think my meter's (Fluke 25 >3digit) getting confused by surrounding circuitry... > >Question is, where do I go from here? Obviously I'm going to desolder one >leg of each of the "suspicious" resistors, but I'm left with three other >possible suspects: > TL431 shunt regulator > PC817 optocoupler > TEA1522 SMPSU controller > >I've already shotgunned all the electrolytics (except the 47uF main >filter) on the grounds that they were made by several known bad-cap >manufacturers (Capxon, JP and one or two others). It's now loaded with >Matsushita-Panasonic parts. So we can call the capacitors "known good" :) > >My plan (after checking the resistors) is to solder some wires across the >5V output, then bring it up to 5V with an external current-limited PSU. >That should allow me to test the TL431 (by increasing and decreasing the >PSU voltage). Testing the optocoupler should be possible too, though I >think I might need a second PSU or a 9V battery for that. > >Can anyone suggest some other things I could check? I'm calling this a >startup issue at the moment, seeing as that's what's happening -- the >SMPSU is failing to start up. > >Thanks, The TEA1522P incorporates the power FET within the IC. It also derives startup power from the drain input. Given that it doesn't drain the mains filter cap, I'd verify no output diodes are shorted, then replace the TEA1522P before wasting time with the opto isolator, shunt regulator, or other unlikely candidate. If you MUST fiddle, use a pair of 9 volt batteries in series to provide startup current via pin 1. (Unless you have an isolation transformer, DON'T use a bench supply). Many SMPS controllers use a large value resistor to obtain startup power. Using an internal switching regulator to obtain startup power is common, and those ICs are prone to failure. This design has gone one step further, incorporating the switching FET in the package, this sacrificing reliability in the quest for high efficiency and low cost. PlainBill
From: Philip Pemberton on 10 Jun 2010 07:52 On Wed, 09 Jun 2010 14:20:22 -0700, PlainBill47 wrote: > The TEA1522P incorporates the power FET within the IC. It also derives > startup power from the drain input. Given that it doesn't drain the > mains filter cap, I'd verify no output diodes are shorted, Output diodes are all A-OK. All around 0.5V forward drop, according to my DMM. > then replace > the TEA1522P before wasting time with the opto isolator, shunt > regulator, or other unlikely candidate. Right, fair enough. I don't like blaming ICs for failures without some proof-of-failure, but in this case I think you're right -- if the FET has blown open, it's not going to be doing much... > If you MUST fiddle, use a pair > of 9 volt batteries in series to provide startup current via pin 1. > (Unless you have an isolation transformer, DON'T use a bench supply). Actually, my plan was to test it with the AC supply disconnected, which would allow me to push a small current into the 5V rail and check that the shunt reg and opto were working. > Using an internal switching regulator to obtain startup power is > common, and those ICs are prone to failure. This design has gone one > step further, incorporating the switching FET in the package, this > sacrificing reliability in the quest for high efficiency and low cost. One more note for the lab notebook! It looks like the chip gets pretty hot too -- there's a lot of discolouration of the PCB laminate around the pins; the diode pads show similar discolouration. In hindsight, that was probably a Big Red Flag... Thanks, -- Phil. usenet10(a)philpem.me.uk http://www.philpem.me.uk/ If mail bounces, replace "10" with the last two digits of the current year
From: Philip Pemberton on 11 Jun 2010 11:29 On Thu, 10 Jun 2010 11:52:17 +0000, Philip Pemberton wrote: >> then replace >> the TEA1522P before wasting time with the opto isolator, shunt >> regulator, or other unlikely candidate. Swapped the 1522. PSU still dead, no output or startup. Suspects are now the opto, the shunt regulator, and the resistors which measured high. -- Phil. usenet10(a)philpem.me.uk http://www.philpem.me.uk/ If mail bounces, replace "10" with the last two digits of the current year
From: Jim Yanik on 11 Jun 2010 12:06
Philip Pemberton <usenet10(a)philpem.me.uk> wrote in news:4c12566c$0$17407$c3e8da3(a)news.astraweb.com: > On Thu, 10 Jun 2010 11:52:17 +0000, Philip Pemberton wrote: > >>> then replace >>> the TEA1522P before wasting time with the opto isolator, shunt >>> regulator, or other unlikely candidate. > > Swapped the 1522. PSU still dead, no output or startup. > > Suspects are now the opto, the shunt regulator, and the resistors which > measured high. > did you check the ESR of the electrolytics,particularly those around your IC? I've seen where high-ESR caps kept switchers from starting. They loaded the IC supply enough that it would not start. I've also seen where carbon film resistors that charged the "housekeeping" IC power supply cap had increased in value to the point they were open. -- Jim Yanik jyanik at localnet dot com |