Samsung FPT5084X/XAA with the BN44-00175A power supply cycles before coming on

I am publishing here, with a customer's permission, a problem related to a Samsung FPT5084X/XAA that both customer and we originally thought was the power supply board BN44-00175A, but turned out something else.

We repair BN44-00175A, but in this case pretty much all the work was done by the customer, so no credit to us for other than posting it publicly in hope it may help someone save time.


QUESTION 1

"Hello,

I have a FPT5084X/XAA with the PS BN44-00175A power supply. 

I bought and installed the capacitors repair kit from Coppell TV Repair (you guys)  and the same symptoms persist.

Symptoms:

panel works but takes quite a few self power cycles to come on. When it does this self on and off the plasma display is primed up when it comes on then you here a click and off, then a click click on eventually you will hear the chime and BAM! the panel comes on.

After the panel has been on and playing and warmed up it will turn on and off fine no issues. BUT if I unplug it for any amount of time it will go back and do the on off on off deal again. Same issue if I leave it plugged in and try turning it on well after its been on and playing.

There is NO issues with the picture it is very clear/sharp and looks great when working.

Trouble Shooting:

I have checked both the VA/VS voltages they are with in spec when the unit is on and playing.

I have visually inspected the PS board for bad cold soldier joints, I couldn't see any (but that doesn't mean I didn't miss em too).

I have repaired several Panels, my soldering skills are pretty good, but this Power supply has me stumped!

The panel has VERY low hours on it, around 5000.

I am interested in your BN44-00175A repair service if you think that will fix the PS, I don't think its an issue with any other board but with Plasma Panels it hard to tell sometimes!

thanks

-jeremy"

ANSWER 1

"See if you can manually activate the board (PS_ON to GND and VS_ON to +5V) and if it does the same strange behavior.

We have another (different) board here, which was sent with practically identical description as yours, but when we test it manually (that’s how we test most of the power supply boards – with artificial and not actual load in an actual TV set) – it works just fine.

So I wonder if you can repeat the problem with the power supply board alone which would give us something to work with."

 

QUESTION 2

"Will do, just to make sure, I am using a jumper wire from PS_ON to GND  and another Jumper wire from VS_ON to +5V and then I plug in the power cord?

I have done something similar for CCFL's to kick on, on non Samsung LCD tvs. 

And if this works, what does this mean?

Thank you Bobby for the quick reply!"

ANSWER 2

 

"Well it means we don’t have an easy way to reproduce the problem.

It may still be in the power supply board, e.g. it may show under specific load conditions which we fail to reproduce properly here, but it may also be a main board or plasma display controller, both of which affect the power on cycle."

QUESTION 3 (PROBLEM FOUND)

"Hi Coppell TV Repair,

just wanted to follow up with you on this.

So after doing some major troubleshooting and swapping out and testing other power supplies and main boards from compatible Sammy Panels who shared the same plugs.

Forcing the power supply to stay on the voltages were spot on perfect for VA/VS and others.

I found out and tracked it down to the main board not sending back the 5v to the PS,  The cause was the CPU and from the looks of it someone tried to reflow it at one point. If Pressed on the CPU sink or used a hair dryer the panel would fire up fine.

So main board replacement, seems to be common problem with these when they heat up around the CPU They sag pretty bad.  Guess I will need to put a support under it.

Anyway thought I would share what I found in case it might be useful for you.

Thanks for taking the time to help me out."

There, hope it helps!

P.S. As I told the customer I do not think that supporting the board - or pushing a processor - is a long term solution to the problem. It probably just needs reflowing. But I'll get into that another time.