Panasonic DMP-BD79 power supply fault.

[soundman2]

HI ALL

I got this blu-ray very cheap from that certain auction site. Didn't pay a lot for it and this thing is less than a year old going by the maufacture date. Anyway, there is a fault causing the fuse to blow on the power board. I put in a Wickmann fuse of the same spec and when I hit the power the fuse lit up before it died (wow). I checked the varistor and its fine. Can anyone give me at least a clue where to start looking for the fault as I'm fresh out of ideas. Diodes seem to check OK. Oh dear, time to get the headache pills ready

[dr.ido]

You've most likely got a shorted switching fet. This may be a standalone fet, or the fet integrated in the power supply IC. If you probe across the pins of the main filter cap (probably a 400V at around 47uF) and find a short this is almost certainly the case.

If it's an IC with an integrated fet they usually don't take anything else with them when they short other than the fusible resistor. If it's a discrete FET with an IC controlling it they can take the IC with them. When they short there will be 300+ VDC on the gate in the brief period before the fuse blows. There are usually diodes/resistors bewteen the output of the IC and gate pin and often they go saving the IC.

Pictures of the board will help if you're still lost.

[soundman2]

I checked across the pins of the mains cap. Does not seem to be a short. I'll try to post pics of the board itself. There is an 8 pin IC. Wonder if that may be shorted? Hmm puzzling.

[soundman2]

Here are the pics of the power board. I changed the mains cap to eliminate it.

[dr.ido]

I wasn't suggesting the main cap itself was shorted, just that it served as a convenient point to test. Apologies for any confusion.

You'll most likely find the 8 pin IC is shorted. These ICs contain the power supply controller and an integrated switching FET. If you can find the datasheet (I can't read the type number in the picture) it will show which pins are which. As it is only an 8 pin DIP, easiest to just desolder it and check the board for the short. If the short is gone with the IC removed, the IC is to blame.

Before replacing the IC check the associated components - looks like there are a couple of small diodes on the top side of the board and a few smd resistors on the bottom - and replace as necessary.

If the short remains with the IC removed the other possibility is the bridge rectifier (circled in the picture).

If this player got hit with a surge it's possible both the rectifier and the IC will be bad.

[dr.ido]

Missed a post up there...

If there is no short across the pins of the main capacitor then look on the AC side of the bridge rectifier. If the rectifier itself isn't shorted that pretty much only leaves that between the AC input and the rectifier - the coil and capacitor that make up the line filter. Not common, but it can happen.

[soundman2]

Thanks for that. Sorry the pics were not clearer as my camera does not have macro facility. Checked the number on the IC and it should be available here in the UK. In the States, I think it's around $12.

[dr.ido]

If you have (or have access to) a pile of scrap DVD players, set top boxes or similar you may be able to scavenge the IC out of one. The same IC my also be used in the standby supply of LCD/Plasma power supply boards.

I find a lot of stuff is only worth repairing using scavenged parts as the cost, delivery cost or lead time for new ones simply isn't worth it. That said, hording a mountain of scrap to pull parts from also has its downside.

That IC would probably be $3-5 from utsource. They're cheap, have cheaper shipping than most, but delivery usually takes 3 weeks (from China to Australia, to the UK will probably be longer).

[soundman2]

The ironic thing about this is....three weeks ago I cleared out a whole load of old panels from my workshop shed. Then I get this item...oh boy. This is Sods Law and it's not a happy one.

Anyway, the silicone diode bridge rectifier is certainly a suspect in this case! I'd love to get this working again. BTW, manufacture date is June 2013.

[soundman2]

The number on the 8 pin IC is 3A153-SK323-G21BA (IC 1021 on the board). There is number on the silicone bridge diode rectifier. The numbers I can make out are A80 and 1532 (D1006 on the board) but that's all. C0DACYY00011 is the part reference in the service sheets.

[dr.ido]

The bridge rectifier is generic, pretty much anyone that will fit (or can be made to fit) will do. The IC is a STR3A153D. No one seems to stock these (at least that I found in a few minutes or googling).

There are several similar parts in the STR3A1xx series that differ only in rated output power and Rds. STR3A151D = 24W, STR3A152D = 30W, STR3A153D = 36W, STR3A154D = 40W, STR3A155D = 43W. The pinout/package is the same for all variants.

Obviously if you can find it order the correct one, but if I found any of the others in my junk pile I wouldn't hesitate to try them.

[soundman2]

Thank you very much for the information . That's given me something to think about regarding the bridge rectifier. I may just get this thing going after all....

[dr.ido]

Crack open a random power adapter. Anything even vaguely recent will be a switchmode type with a suitable rectifier in it. You may even get lucky and find the IC.

[soundman2]

Superb info, many thanks.