Help with Tatung TLM-1905 LCD no power at all

[jbshocks]

Re: Help with Tatung TLM-1905 LCD no power at all

Thanks Rtech, I will order one up from digikey and give it a shot.

[jbshocks]

Re: Help with Tatung TLM-1905 LCD no power at all

I changed out the chip and the little 22uf cap. Symptoms the same. Only difference now is that I get 3.3v between pin 5 and 7. Still no voltage on board connector.

[jbshocks]

Re: Help with Tatung TLM-1905 LCD no power at all

what about this little chip? It is P721F, call a switching power supply. How would I test it. Could it be the cause? I have power on the two legs with in the zone that power works.

[budm]

Re: Help with Tatung TLM-1905 LCD no power at all

That is an Optoisolator for the voltage regulation feedback circuits.
"I get 3.3v between pin 5 and 7 " Are these the pins of the long white connector that the wires go to the main board?

[jbshocks]

Re: Help with Tatung TLM-1905 LCD no power at all

The 3.5 I get on the little 8 pin chip sg3842gs that I replaced. I also get 3.5 across the small 22uf cap. I get nothing on any pin of the white connector going to the other board.

[budm]

Re: Help with Tatung TLM-1905 LCD no power at all

OK, lift up one leg of the white fuse and then check the voltage on those two pins as shown in red circle. You can run the board by itself just have the power cord attach to it.
Can you also take the straight shot of the bottom side of the board, the pictures you posted are tilted and it is hard for me to trace out the connections.

[jbshocks]

Re: Help with Tatung TLM-1905 LCD no power at all

OK, lift up one leg of the white fuse and then check the voltage on those two pins as shown in red circle. You can run the board by itself just have the power cord attach to it.
Can you also take the straight shot of the bottom side of the board, the pictures you posted are tilted and it is hard for me to trace out the connections.

So un solder the fuse and test for power? I ca do that after work but I don't think there will be anything. There is no sign of power on that side of the main yellow transformer.

[budm]

Re: Help with Tatung TLM-1905 LCD no power at all

I just want to make sure that it is not in the safety shutdown mode due to shorted circuit in the inverter circuits, that white fuse feeds the B+ to the inverter circuits.

[jbshocks]

Re: Help with Tatung TLM-1905 LCD no power at all

removed fuse. no voltage on either pin or across them. I will try to get another picture later.

[jbshocks]

Re: Help with Tatung TLM-1905 LCD no power at all

see if this picture is better

[budm]

Re: Help with Tatung TLM-1905 LCD no power at all

In the last picture, i can see clamping Zener Diode ZD102 (on the bottom side of the board), can you take the resistance reading?
By the way, did you also replace this small cap, it has bulging top. I do not see any soldering works on its two solder pads.

[jbshocks]

Re: Help with Tatung TLM-1905 LCD no power at all

diode check 470 one direction and 143 the other ohms 89.8 one direction and .46 on 20k scale other direction. By the looks of it I did not change that little cap. I will see if I have one. It doesn't look bulged in person