Tuesday, April 22, 2014

Philips 42PFP5332D/37 dead, power clicking on and off

Today I've seen something that I do not think I've seen once in the past 3-4 years so I decided to show it.

A power supply board SAMSUNG PS-426-PH / LJ44-00143A came in today, from a PHILIPS 42PFP5332D/37 plasma TV.

The customer had actually sent it by mistake because we do have a listing for another power supply board used in a different chassis version of the same TV model:


Well the board in the above listing is NOT PS-426-PH / LJ44-00143A , but the customer went by the model number and we ended up with a board we have not worked on before.

Here is your Samsung  PS-426-PH / LJ44-00143A for Philips 42PFP5332D/37:
 (the picture is of the actual customer's board; they had their contact info written on it so I had to smudge it a little with Gimp; I am sure there are better ways to do it, but I just smudged it).

It had a blown 4A fuse (F8005 located between the two large capacitors in the middle of the board) and a quick test showed barely a few ohms resistance from the inside part of the fuse to ground - a pretty darn good reason for blowing if you ask me.

Nothing unusual so far, right?

Well, I tested the power FETs and they were good.

I tested the power driver ICs for the Va/Vs transformers (they are separate on that board) and they were also good - nothing remotely close to short.

There aren't many other power components on the other side of that fuse, honest.

After 15 minutes of finding nothing I started desoldering the primary windings connections on the transformers....still nothing.

The only really LARGE and powerful component I have not checked was the filter capacitor
C8054 (220uF/450V) , one of the two large capacitors around F8005 on the picture.

I did not check it for two reasons:

First, it didn't look bulged, worn out or anything unusual, at least from the top; it's a little tight there so it was hard to see it all, but again nothing significant.

Second, I do not remember having ever seen a large capacitor like that short out; I've seen many dry and get infinite ESR, but I haven't seen a shorted one.

Well lo and behold:

A steady low resistance on a capacitor this size and voltage was something I saw for first time in long enough to feel like first time ever.

That turned out to be what killed the fuse.

Just for the record, C8023 was visually swollen and had to be replaced and the Vs output filter capacitor was also bad although still functional. I have not taken its number, sorry, but it was 820 uF/250V and when I pulled it out it was doing the same rattling sound when I was shaking it that the bad one on the picture was doing..only it wasn't shorted.

Hope this helps someone!


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