EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Selleli on December 25, 2019, 05:31:45 am
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Hi. I need help repairing a Philips DVD Player.
The symptom is, that the player is not turning on. And the control panel on the front remains completely dark (no lights). Apparently, there is a fault in the power supply (PSU). The output wires in the connector CN502 (12V ones as well as 5V ones) only show around 0.1V instead of their designated nominal voltage. And the voltage is heavily unstable, so that it's hard to get a good voltage reading with the DMM.
I have tested many components already. Including the full bridge rectifier and of course the mains fuse. But so far, I can't pinpoint the fault yet. All tested components appear to be fine.
Note: The voltage selector jumper is currently open, which is the correct setting for 230V. It would need to be closed for 110V.
Front of the PCB:
[attach=1]
Backside of the PCB:
[attach=3]
I am keeping track of which components I have analyzed already. See my results in the Excel file:
[attachurl=2]
Any good hint how I should proceed next to pinpoint the fault?
Thanks!
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Pull up the datasheets for the switch control ICs and start checking for the correct voltages and waveforms at each pin of the ICs. The datasheets typically contain a lot of valuable information including start-up sequence and what conditions need to be met for the IC to operate and produce switching waveforms.
WARNING: an isolation transformer or an isolated scope probe is a MUST when using an oscilloscope on the primary side of a SMPS.
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The switching IC looks like the drain pin has blown open and if you look closely unless I'm mistaken another pin blackened. So check that closely and all those diodes around that area, then optocouplers and those two capacitors next to the IC for capacity and ESR, it's common for them to fail in that area.
Edit:
This board looks like it has been reworked as well, there is a bad solder joint on a diode below the IC on the back side, just a reminder in case that was you. Also check all fuses and resistors transistors etc. It's in need of a good clean with some IPA and a close inspection or continuity check to ensure no traces are damaged otherwise it may go bang again if the cause is not found.
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The switching IC looks like the drain pin has blown open and if you look closely unless I'm mistaken another pin blackened. So check that closely and all those diodes around that area, then optocouplers and those two capacitors next to the IC for capacity and ESR, it's common for them to fail in that area.
(..)
Yes the pin looks missing... toasted?
That is the DRAIN of mains switching on direct forward single switch
aka primary side switcher..
Take care on that
Paul
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D506 has a bad joint and also JMP17 and D505 look a bit rubbish to be honest, unrelated to the original problem.
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I'd say CE515 needs to be re-soldered as well. Probably more components, when taking a closer look.
Awful soldering on this board :--
Btw. the diodes on my Philips Ambilight PSU were blown too, this seems to be a very common problem (pre-planned point of failure), so certainly check those.
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Thanks so much for all your contributions!! :-+ I am really amazed how much help I am getting here!
Indeed: The drain pin of the switching IC is indeed toasted! I am stunned! :scared: I have never seen a pin completely toasted like that. And I am embarrassed that I haven't noticed that myself. I have already ordered some new spare units. And in the meantime, I will take care of the other tips given (bad solder joints). And I will check whether any other bad component connected to the switching IC could have caused the IC to fail.
So, for the moment, I know what I need to work on. Thanks!
PS: Thanks for the warning about using the oscilloscope on the primary side of a PSU. Unfortunately I am still missing an isolation transformer. It feels very hard to find here (currently staying in the Philippines)... So I won't risk using my oscilloscope on that PCB at all. To remain safe.
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I somehow completely missed the missing pin and burn marks when looking at the photos! Yeah, that's definitely toasted.
It's not that unusual for SMPS to fail in that manner. When the switching FET fails short, the fuse doesn't always blow, as the energy stored in the primary filter capacitor can be sufficient to blow the bond wire in the FET, which either splits the case of the FET/IC apart or initiates an electrical arc that vaporizes the pin away.
Sometimes the failure can be very spectacular especially in larger high power PSUs, sending sparks and transistor case shrapnel flying across the room (if the cover's off anyways).
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Do inspect all diodes as mentioned, for example ZD503 looks visually cracked?
There also appears to have formed an electric arc not only between pins 6 & 7 on the TinySwitch controller:
But also between those pins and JMP19, which seems crazy, lightning strike perhaps?
When testing this power supply use a dim bulb tester (incandescent lamp of 60w to 100w replacing the fuse or in series with the incoming mains)
That way you will not blow up another TNY chip if you have not found the root cause of the failure...
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I suspect the problem started out as faulty electrolytic capacitors and that caused something else to blow up. Last year I had to fix my mom's TV, the power supply for the light engine (LED DLP) blew up so I replaced the bad parts, tested it on the bench and it worked so I put it back in the TV, hit the power and BANG. Pulled it out again and did further testing, turned out the main bulk filter capacitor was completely open circuit. Replaced that and again replaced the other parts that blew up and that fixed it. With no load it would run on the bench without the bulk filter but under load in the TV that wreaked havoc and it would blow up instantly.