Samsung SyncMaster 943BM - backlight only for half a second

[Behemot]

Re: Samsung SyncMaster 943BM - backlight only for half a second

It is fine, it's just a flash. It's PWM with integrated MOSFET - if it would be bad I would see lot of smoke and burning with 325 V DC in there, and no voltages on secondary side. But they are OK.

[selldoor]

Re: Samsung SyncMaster 943BM - backlight only for half a second

Tried jumpstarting power board with a resistor or 3v battery
to see if the lights come on without the main board?

[Behemot]

Re: Samsung SyncMaster 943BM - backlight only for half a second

Nope that was with the signal board in there. You mean resistoring the BL_ON? What resistor, couple kiloohms?

[addytzu123]

Re: Samsung SyncMaster 943BM - backlight only for half a second

I don't think it's necessary, according to the voltages posted, on pin 10 wich is Chip Enable there are 2,89 V, well above the 2V treshold.
Also the 5,13 V on the Vdd pin indicate a correct operating voltage...
Voltages on pins 3 and 12?

[Behemot]

Re: Samsung SyncMaster 943BM - backlight only for half a second

0 V both. It flashes to 0,6 V and 1 V for the short time when the lamps light. The No. 5 pin flashes up to 0,7 V briefly. I've tried different panel with 3rd set of lamps, same behaviour so definitelly not CCFL problem.

[Davi.p]

Re: Samsung SyncMaster 943BM - backlight only for half a second

"I've tried different panel with 3rd set of lamps" That panel had same size ? CCFL was known good? Different inverters can make some old lamps work when another not.

[Behemot]

Re: Samsung SyncMaster 943BM - backlight only for half a second

OFC all of them 19'', I have some standalone lamps but all of them bigger (from 22'' displays mostly).

[Davi.p]

Re: Samsung SyncMaster 943BM - backlight only for half a second

Transformer is surely good?

[Behemot]

Re: Samsung SyncMaster 943BM - backlight only for half a second

Secondary surely is, as for primary, no way to measure, the inductance is too low.

[stj]

Re: Samsung SyncMaster 943BM - backlight only for half a second

too bad nobody uses a "ringer" anymore!
lucky i still have mine fron lopt testing days.

[Behemot]

Re: Samsung SyncMaster 943BM - backlight only for half a second

?

[selldoor]

Re: Samsung SyncMaster 943BM - backlight only for half a second

Ring tester -- google it funnily enough i was reading a thread started by Plainbill as
he couldnt work out what was wrong with a monitor. Inverter transformer tested ok
but was still faulty - he used a ring tester.

[stj]

Re: Samsung SyncMaster 943BM - backlight only for half a second

http://members.ozemail.com.au/~bobpar/fbt.htm
http://preher-tv.blogspot.co.uk/2010...ng-tester.html
schematics downloadable to make your own!

[Behemot]

Re: Samsung SyncMaster 943BM - backlight only for half a second

I guess I could take it next time from Mikhail, he also has some versino of that…until than, could take the transformer itself and just try a blind swap :-) I have a TM-0917 on the way, do you think it would be posible to swap it for this TM-1017?

[selldoor]

Re: Samsung SyncMaster 943BM - backlight only for half a second

http://www.lcdparts.net/TransformerD...ProductID=3721
http://www.lcdparts.net/TransformerD...ProductID=3720

Only 8 ohms diff on the secondaries - if pin alignment is good should be ok

[budm]

Re: Samsung SyncMaster 943BM - backlight only for half a second

The DC resistance of the winding cannot be used alone, the inductance has to match the transformer and the turn ratio. You can have transformer with the same ratio, one may use smaller wire gauge so it will have higher DCR but the current will be less. or you can have the same resistance reading but the turn ratio is not the same because of the wire gauge use, one with less turn but smaller wire can have the same DCR as the one with bigger gauge wire with more turn.

[Behemot]

Re: Samsung SyncMaster 943BM - backlight only for half a second

I think that as the physical dimensions are 100% same and there is only 8 ohm difference, plus the CCFLs consume the same current, this will probably not be the case of more turns with thicker wire, yes?

[budm]

Re: Samsung SyncMaster 943BM - backlight only for half a second

Turn ratio will determine the output voltage, DCR is not the way to find out if the transformer is compatible or not, the switching DC is being applied to the winding so Inductance value is important numbers. Without know the deatils spec of the original, it will be difficult to know if the circuit can handle the sub transformer or not. They can use the same core for more than one model of the transformer.
Read the info on the link here:

look at page 13 and later.
I had done experiment with sub transformer that seems to be close to the original without know the details spec of the original, the inverter circuit failed after a couple weeks of operation, it took out the MOSFET's with it.

[selldoor]

Re: Samsung SyncMaster 943BM - backlight only for half a second

Is this a scenario where the one wire cfl trick might help?


https://www.badcaps.net/forum/showpo...27&postcount=1

[Behemot]

Re: Samsung SyncMaster 943BM - backlight only for half a second

Turn ratio will determine the output voltage, DCR is not the way to find out if the transformer is compatible or not, the switching DC is being applied to the winding so Inductance value is important numbers. Without know the deatils spec of the original, it will be difficult to know if the circuit can handle the sub transformer or not. They can use the same core for more than one model of the transformer.
Read the info on the link here:

look at page 13 and later.
I had done experiment with sub transformer that seems to be close to the original without know the details spec of the original, the inverter circuit failed after a couple weeks of operation, it took out the MOSFET's with it.

I'll measure the inductance, if it will be close enough, than keep it, if not, than order the original one. I don't even know right know if the problem indeed is in the transformer or not so for testing it is the best I will have.