Samsung 930B re-capped, no backlight

[alexanna]

Re: Samsung 930B re-capped, no backlight

I have a 939B that is not working.
All the 10mm and smaller caps have been replaced they were obviously swollen. And have been replaced this includes the two 4MM caps.
U202 and U203 had similar damage as the OP board. And have been replaced.
I have a power supply that is starting and shutting off repeatedly, the power LED is flashing on and off
I am currently looking at the DM0565R power switch
http://pdf1.alldatasheet.com/datashe...SDM0565RB.html
I have taken some voltage measurements
Pin 1 is fluctuating between 150 and 160V D.C.
Pin 2 dose have a ground
Pin 3 is fluctuating between 9 and 15V D.C.
Pin 4 which is the feed Back is Fluctuating between .5 And 8 V D.C.
Pin 5 not used
Pin 6 is fluctuating between 32V D.C. and 159 V D.C.

I guess i should have said anybody got any ideas on what to check

[retiredcaps]

Re: Samsung 930B re-capped, no backlight

Pin 1 is fluctuating between 150 and 160V D.C.

Is the DC voltage stable across the main filter capacitor?

[alexanna]

Re: Samsung 930B re-capped, no backlight

It stays at 160V to 161v the majority of the time, using the min max record it will go as low as 149v briefly at times

[alexanna]

Re: Samsung 930B re-capped, no backlight

The voltage is steady at 163v across the big cap with the logic board unpluged

[Scenic]

Re: Samsung 930B re-capped, no backlight

r316 looks pretty toast.. doubt it has something to do with this though..

[retiredcaps]

Re: Samsung 930B re-capped, no backlight

The voltage is steady at 163v across the big cap with the logic board unpluged

Sounds like something on the logic board is pulling down the power? I had something similar, but never managed to resolve due to a slip of the hand and shorted out some components on the power board.

I don't have any ideas. Maybe PlainBill does?

[jetadm123]

Re: Samsung 930B re-capped, no backlight

The voltage is steady at 163v across the big cap with the logic board unpluged

With the logic board unplugged, do you still have the fluctuating voltages at pins 3 and 6 of the DM0565R?

[alexanna]

Re: Samsung 930B re-capped, no backlight

logic board unpluged
Pin 3 steady 10.4v
Pin 4 steady .284v, and
Pin 6 steady 157.8v

[Mikeley]

Re: Samsung 930B re-capped, no backlight

What voltages can you measure on the CN2 connector now??
Have you got stable 5V and 13V?

[alexanna]

Re: Samsung 930B re-capped, no backlight

I am seeing stable 5.16,and 13.14v without the logic board conected

[retiredcaps]

Re: Samsung 930B re-capped, no backlight

Here is an idea which could be completely invalid. Others with more experience can comment on the validity of this idea. Do not try it unless someone else has done it.

Instead of using the supplied connector from the power board to the logic board, solder temp wires in place. The idea is to figure out which "rail" is causing the the power board to fluctuate.

So maybe start with just soldering in temp wires for ground. Retest for fluctuating voltage. If stable, then add 5V. Retest voltage. Etc, etc. Maybe this will help narrow down the problem?

[jetadm123]

Re: Samsung 930B re-capped, no backlight

I'd like to add on to retiredcaps idea by suggesting the following: If you have a spare 12V automotive tailight bulb, (with the logic board still disconnected) try connecting it across the 13V output of the power supply. It would be interesting to see if any load causes the power supply to shutdown.

[PlainBill]

Re: Samsung 930B re-capped, no backlight

These are good suggestions; I'm going to throw my thoughts in here.

Possibilities:

1. The power supply is unstable with any significant load - suspect the large cap.

2. The power supply is reacting to an excessive load generated on the logic card or LCD panel.

3. The power supply is reacting to an excessive load generated on the power supply board - the inverter.

PlainBill

[alexanna]

Re: Samsung 930B re-capped, no backlight

I didn't say this in my first post,I never see a on off siginal at the conector from logic to p/s.

Yes i have 12v lamp let me see what happens

[retiredcaps]

Re: Samsung 930B re-capped, no backlight

1. The power supply is unstable with any significant load - suspect the large cap.

Sounds like a good opportunity to raid one off a "junk" board for test purposes.

[alexanna]

Re: Samsung 930B re-capped, no backlight

I'd like to add on to retiredcaps idea by suggesting the following: If you have a spare 12V automotive tailight bulb, (with the logic board still disconnected) try connecting it across the 13V output of the power supply. It would be interesting to see if any load causes the power supply to shutdown.

With the logic board unplugged, the tail lamp of a 1157 bulb will light dimly I am guessing that will be close to 700MA.The turn signal filament will not light.
I have a test light that uses a much smaller bulb and it will light on the 5v and 12v circuits.

[Mikeley]

Re: Samsung 930B re-capped, no backlight

It is likely to be the 5V rail powering the logic PCB having an excessive load.
But the PSU may also still have a problem with it's feedback circut and the backlight Inverter could have trouble!

First, isolate and eliminate shorts from logic PCB causing the overload condition in the powersupply:
If you have another logic PCB, substitute it. Otherwise, check the 5V and ground wiring back through the connector to the logic board.

Check for shorts by measuring resistance across each of the voltage regulator pins... now I dont have a diagram, but I suspect they are the 3 leg terminal devices circled, one or more of these may be shorted. One produces 1.8V and the other 3.3V?? Measure resistance between each of the terminals.

Second
Looking again at the power board, have the inverter FET's been replaced, U203 looks like the solder has accumulated one one side shorting out one side of the dual FET, could you verify this? Were FET's replaced? And R316 is toast, likely to be open circuit. It appears to be connected to pin 8 of U201 but I can see it clearly from the picture. Anyone have the value of this? 10R or 1R maybe? There is more than one problem to solve. Start with these.

Mike

[alexanna]

Re: Samsung 930B re-capped, no backlight

I just measured this with the tail lamp filament the draw is 912MA on the 12v rail.

[alexanna]

Re: Samsung 930B re-capped, no backlight

It is likely to be the 5V rail powering the logic PCB having an excessive load.
But the PSU may also still have a problem with it's feedback circut and the backlight Inverter could have trouble!

First, isolate and eliminate shorts from logic PCB causing the overload condition in the powersupply:
If you have another logic PCB, substitute it. Otherwise, check the 5V and ground wiring back through the connector to the logic board.

Check for shorts by measuring resistance across each of the voltage regulator pins... now I dont have a diagram, but I suspect they are the 3 leg terminal devices circled, one or more of these may be shorted. One produces 1.8V and the other 3.3V?? Measure resistance between each of the terminals.

Second
Looking again at the power board, have the inverter FET's been replaced, U203 looks like the solder has accumulated one one side shorting out one side of the dual FET, could you verify this? Were FET's replaced? And R316 is toast, likely to be open circuit. It appears to be connected to pin 8 of U201 but I can see it clearly from the picture. Anyone have the value of this? 10R or 1R maybe? There is more than one problem to solve. Start with these.

Mike

There are no shorted v regulators
The fets have be replaced, the solder glob is on the drain pins and all of the pins are conected together on the PCB
The logic board is not even asking for backlights,there is no on off siginal

[jetadm123]

Re: Samsung 930B re-capped, no backlight

I just measured this with the tail lamp filament the draw is 912MA on the 12v rail.

Out of curiosity, with the tail lamp connected, are the voltages on pins 3,4 and 6 of the DM0565R still steady?