Samsung 930B re-capped, no backlight

[alexanna]

Re: Samsung 930B re-capped, no backlight

Alexanna, I looked at your pic of the underside of the power supply board and I'm assuming U202 and U203 have been replaced because they have no obvious burns on them, U203 doesn't look like it's soldered correctly (or it could be the lighting.. )

carry on...

update: still waiting for my parts

The problem really looks to be in the inverter area.
I have removed the Fet with the questionable solder, those 4 pads are on the drain of the Fet and all 4 pads show continuity to each other. Any way I removed and reinstalled the FET so there are no globs.
Something is happening the problem is getting worse, now with the logic board disconnected, the Fet that I just installed got so hot it melted the solder of the board. I am not finding any of the pads shorted to ground.
I used some Fet's I Had in stock, They appear similar to me but the amperage is rated lower, I wonder if that could cause this problem?
http://search.digikey.com/scripts/Dk...=FDS8958ACT-ND

[leperinc]

Re: Samsung 930B re-capped, no backlight

Alexanna, I looked at your pic of the underside of the power supply board and I'm assuming U202 and U203 have been replaced because they have no obvious burns on them, U203 doesn't look like it's soldered correctly (or it could be the lighting.. )

carry on...

update: still waiting for my parts

[jetadm123]

Re: Samsung 930B re-capped, no backlight

I will need to check that just a little later dinner calls

Please disregard what I had asked for earlier. The bulb is drawing more current than the 13V output is capable of putting out, which accounts for the dim light.

[Mikeley]

Re: Samsung 930B re-capped, no backlight

What readings did you get for each regulator? Last questions for tonight, did you have boards back in the metal chassis frame with all screws back in when you had the logic board connected and powered with problem present?

Was the LCD and front panel also connected to the logic board at the time? Try with everything connected once more, if that was the case, remove the LCD panel connector, check 5V and 13V.

Reconnect and remove front panel, remeasure voltage in order to eliminate each of these.

[alexanna]

Re: Samsung 930B re-capped, no backlight

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

I will need to check that just a little later dinner calls

[alexanna]

Re: Samsung 930B re-capped, no backlight

I am beginning to wonder if something may be wrong in the inverter section.
With the logic board unplugged providing 3.3 volts to the on off pin causes the back lamps to come on but they resemble a Florissant light with a defective ballast flickering rapidly.

[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?

[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

[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.

[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'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.

[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 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

[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

[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.

[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?

[alexanna]

Re: Samsung 930B re-capped, no backlight

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

[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

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

[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?