Tuesday, February 24, 2015

Repair dead Samsung HPS5053X/XAA, bad PSPF501A101A power supply

A customer brought in an old Samsung HPS5053X/XAA.

We've repaired and sold a lot of Y-Main boards for this TV in the past , but when we moved to our current location in the middle of 2014 we broke our own unit and haven't been able to repair and sell those boards anymore.

So naturally we assumed the problem was in the Y-Main, but it wasn't.

The TV was totally dead and that pointed towards the power supply, which is PSPF501A101A :

We tested the board in-place (in the TV) and it was lacking 5V standby.
All fuses tested out good and we had to take it out for further investigation.

All power components tested good and there were no visibly bad electrolytic capacitors.

We ended up finding the rectifier for the standby voltage output being shorted. 
This is the diode DB864 that sits on the secondary winding of the small transformer producing the standby voltage:

On the above picture the diode is already taken out of the board, sorry.

It was SB5H100, which  is a 100V / 5A rectifier.

It doesn't need 100V on the secondary side of the standby and frankly I am surprised it needs 5A, but if they used it then probably there was a good reason for it.

We didn't have a through-hole 5A/100V diode, so we used an SMD one that  we put on the other side of the board:

The board worked just fine afterwards and so did the TV.

Hope this helps someone save $100 or so for a replacement board.

Saturday, February 21, 2015

IC2 for MLT198L

It feels like we're getting somewhat of a "last hope" outlet for people with hopelessly old TVs :-)

An MLT198L power supply from ILO LCT42HA36 about my age was sent to us with request to repair it as parents or grandparents are attached to the TV.

After doing some digging on the board and digging online I found that people were stumbled trying to find replacement for the PWM driver IC for the standby circuit.

At least in few different online discussions the question has been asked and wasn't answered.

Oddly, there's a schematic for the board available (google for it, you'll find it) and there in place of the IC label there is just a question mark (?).

That tells me someone even more dedicated than us must have spent the time to not only reverse-engineer the schematics of the board, but also put it in a CAD and post it.

Either that or took an original and removed the label of the IC.

I choose the former.

Anyway, we have IC2 for MLT198L available at our online store if anyone still needs it.

Thursday, February 19, 2015

Repair LJ44-00143A / PS-426-PH power supply out of Philips 42PFP5332D/37

This board is from the fairly old Philips 42PFP5332D/37 plasma TV, but we received it from a customer with request to repair as they said they couldn't find it anywhere and nobody wanted to help them.

The board had a blown main fuse so the whole TV was totally dead (which correctly pointed the customer to the power supply), but all power components bench-tested fine.

So we replaced the fuse, took cover and plugged it in.

It took a second, but the board started crackling and sparkling.
I actually can not testify to the later as I was careful watching elsewhere (I always do when I test power boards), but I definitely heard it.

All the commotion has somehow gotten the tech working on the board by surprise since I could hear the crackling sound for long enough to start debating in my head if it is from a failing thermistor or what.

The failing thermistor was the best I could come up with.

Then AC was stopped and the board went quiet. Strangely, the main fuse was still good.

The brave tech said that the sparks have come from the sub-module between the second and third heat sink left to right. You can see his mark and arrow pointing to it at the above pictures.

However, when inspecting the sub-module I found nothing that would match the fairly loud cracking I've heard for 5 or so seconds. A small board like that should have been fairly well smoked.

Nothing was - nothing on the sub-module, noting else around.

So, after some meditation and recollection of past experiences I opted to take out the two large filter caps (which seemed fairly well and were holding well too).

I found this:

Considering this was my first try on the board I figured today must be my lucky day and called my wife probing my chances for the night. She said she's planning to have a headache again so for your luck I continued doing the board instead.

Now, the extensive burn looks pretty bad at a first glance, but after some cleaning we got this:

You can now see the track going left to right that was almost fully burned. The coat has been cracked and wiped away and you can see the copper there as well as the burned PCB layer underneath.

I bring this up because when the PCB layer burns it is important to cut or scratch it out until you get to a good material. This is because burned PCB tends to have very low resistance and is a great risk for repeat arcs that can do more damage.

The task is not unlike that of a good dentist - all bad material has to be removed until you hit solid one and only then the actual restoration can begin.

This is true for all PCB burns. I've seen it a few times in sustain boards and many times in plasma buffer boards.

So we scratch the burned PCB and take extra care around and under the edges of the damaged track.
If necessary - and it is necessary - we break the track to make sure we eliminate the bad material underneath it:

As you can see I've cut the copper track and made the hole bigger only so I can be sure there's no more burnouts.

Now, there were several possibilities for restoration.
I considered running a cable at the back side of the board. It would have been the safest and easiest approach, but the track going to the LEFT (under the heat sink) splits into three smaller ones, each of which gets a contact point I could run a wire to, but it would have given current to the other two at 1/3rd of the width of the original track.

Chances are it would have been all right, but I decided to run a jumper there, right under the capacitor.

That means it'll have to be lifted (will have to use silicone to prevent vibrations) and that I'll have to take extra care for separating the jumper from the capacitor.

Here is how it went:

 The last step was covering the two soldered ends of the jumper with coating. I did that, but forgot to take a picture and then left the shop.

Tomorrow I may cover the whole thing once more with some insulation and debate on whether to place something at the other side of the center of the capacitor to make the raising even.

Either way, the important thing was to show a problem on a board that can't be found and which is likely going to happen on others due to their aging plus bring attention to the proper way of addressing the burnout PCB issue.

While looking at the board I noticed a few smaller capacitors that did show signs of aging . Tomorrow I'll go through some if not all of them with an ESR meter, replace the ones that are off and try the board again.

I am pretty certain the board will work.

In case you haven't noticed I am good at doing boards.

And not so much my wife.

Thursday, February 12, 2015

Repairing 1AA4B10N2020A / PWB.CONTROL.N4SG button board for Sanyo DP42647 , Sanyo DP42848

I never thought I'd be blogging about such a thing, but two events not too far apart from each other made me.

First, about a month ago while ghosting around before leaving the Coppell TV Repair shop for the day I manager to somehow kick one of the Sanyo TVs we have sitting on the floor for testing repaired main boards and broke its buttons board.

Naturally, I cursed loud and set to fix it, checking first if it isn't just cheaper to buy one.

To my surprise there was none on eBay!

I mean yes, people don't keep their TVs open on the floor and kick them every now and then like I enjoy doing before dinner, but this is eBay where you can things like "Vintage Batman Anchor Hocking Milk Glass Cup, National Periodical Publications" and that's even before getting to erotic periodicals from the 40s that can only turn on (in my opinion) the camp fire and still with external help.

Anyway, I had to fix it and after some more cursing I got it to work and forgot about it.

Then a few days ago one of our customers asked if we can find that same board for him because he broke his.

And today his came and I fixed it again. It was broken in a very similar fashion.

Repairing is not a rocket science, but requires fine sold tips, solid hand and some patience.

On the above picture you can see how I've added one metal rod (what's the better word for that) for support on the top of the board and here's the bottom:

If you happen to break your board and can't fix it yourself feel free to drop us a line.

It'll be about $25-$30 in total (as it takes a good 20 - 30 minutes)  and the best way to start is through http://www.coppelltvrepair.com/newservice .