samsung plasmas & lightning

[heavymachines]

Re: samsung plasmas & lightning

They are simply a bridge rectifier made of pairs connected in a parallel.
Two big caps are connected down the line to the Y-Main connector.
Caps look good and the connector was unplugged. I also checked Y-Main board connector for short and it looks good.

ok, i been looking for them diodes seems like china is the source so far.

[zape]

Re: samsung plasmas & lightning

Hmm these diodes are difficult to replace.
I assume they are schottky and not general purpose and should have Insulated tab.
Cant find any available on digikey
Don't trust Chinese sellers

[heavymachines]

Re: samsung plasmas & lightning

Here is the data sheet. Fast Recovery Diodes

[zape]

Re: samsung plasmas & lightning

I think I will order these from digikey:
SDURF2030CT
A bit higher recovery time but still fast and has insulated tabs

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Re: samsung plasmas & lightning

Decided to change to 400v diodes and ordered SDURF2040CT

Calculated 300v is too low for this rectifier given output voltage of 202v and probably the cause of initial failure.
Theoretically the voltage should be 202 * Pi /2 = 317v so 300v is too low

[zape]

Re: samsung plasmas & lightning

Replaced the diodes but the Power supply still shuts down as in the beginning.
Probed the Vs test point and it looks like it is overvoltage protection.
I got almost 300v instead of 202v before it shut off.

Power supply P/N is BN44-00281A
Anyone familiar with this board? What should I check first?

[zape]

Re: samsung plasmas & lightning

Ok guys I figured out the Power supply is OK (and probably was before I burned it)
It just turns off automatically without load.
When I connected a load (two 40w bulbs in series) it turned on and worked just fine.
I guess it is Y-sustain board which is faulty then.
P/N: BN96-09768A (LJ92-01566A)
PCB Number: LJ41-05754A

[zape]

Re: samsung plasmas & lightning

Found suspected zener diode on the board but it is in a parallel with this resistor.
Can't figure out what should be the Ohm value.

[heavymachines]

Re: samsung plasmas & lightning

Found suspected zener diode on the board but it is in a parallel with this resistor.
Can't figure out what should be the Ohm value.

Resister most likely fine.

[heavymachines]

Re: samsung plasmas & lightning

Ok guys I figured out the Power supply is OK (and probably was before I burned it)
It just turns off automatically without load.
When I connected a load (two 40w bulbs in series) it turned on and worked just fine.
I guess it is Y-sustain board which is faulty then.
P/N: BN96-09768A (LJ92-01566A)
PCB Number: LJ41-05754A

When you had it stay on did voltages read correctly as the sticker on panel ?

[heavymachines]

Re: samsung plasmas & lightning

Y sustin , did you check transistors for shorts, did main input connect have high resistance to ground? if you have ceramic resistors do they read correctly value should be labeled on it. , did you check for dry joints?

[zape]

Re: samsung plasmas & lightning

Yes the Vs and Va voltages were correct.
When I connect Y-sustain instead of the bulbs the power supply behaves as there is no load - Vs voltage goes to the top and it shuts down (probably because of overvoltage)

So it is like Y-sustain does not load the power supply for some reason.

Yes I checked all big transistors for shorts, also checked for dry joints.
The main input behaves just like a capacitor
The board also produces correct Vscan voltage (-190v)

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Re: samsung plasmas & lightning

I got the TV working. Kind of.
In order to start the power supply I have to load it additionally with two 40w bulbs. After the TV is on I can disconnect the additional load and it continues to work fine. All panel voltages are OK.

So it seems that the power supply is faulty, probably feedback/protection path is not working correctly (at least in the very beginning). This power supply is quite complex though, it has TI MSP430 microprocessor doing something...

[zape]

Re: samsung plasmas & lightning

Finally fixed the power supply.
It was bad capacitor CS831 (47u 50v)
The cap looks good (see photo) but I figured out it was bad by soldering a new cap in a parallel.
There are four of these on the board close to the heatsinks so I will replace them all.