Westinghouse A190E3-H01 no backlight / shutdown

[caphair]

Re: Westinghouse A190E3-H01 no backlight / shutdown

"Mosfet Ics I measure:
S1-D1(Two D1 pins) 570ohms
S2-D2(Two D2 pins) 530 ohms

S1-D1(Two D1 pins) 570 ohms
S2-D2(Two D2 pins) 529 ohms"

Those are tested off the board and probe in both directions? There is body Diode on Source and Drain pin, so in one direction it should show as open circuit.

In circuit and yes they show open in the opposite direction. When I had them out of circuit they tested the same, though I do not remember exact values.

[budm]

Re: Westinghouse A190E3-H01 no backlight / shutdown

That is fine then, we are looking for something <50 Ohms.

[caphair]

Re: Westinghouse A190E3-H01 no backlight / shutdown

When the backlights quickly flash, there's a very high pitched noise associated with them.

Also the high pitch noise is present with the monitor off, then it stops when turned on and then heard louder with backlight's attempting to illuminate.

So the transformers are fine? Am I wrong to have assumed there should be no reading between primary and secondary points?

[budm]

Re: Westinghouse A190E3-H01 no backlight / shutdown

The inverter transformer high voltage winding has on end connected to the sensing circuits to detect if the lamp are connected or not or if the lamp does not stay on, it is not isolated circuit.
"Also the high pitch noise is present with the monitor off, then it stops when turned on and then heard louder with backlight's attempting to illuminate." OK that is one of the important info. i thought it only squeals when you turn on the monitor.
I would re-cap the board at this point, also check the solder joints, rectifier diodes on the secondary side of the power transformer, etc.

[caphair]

Re: Westinghouse A190E3-H01 no backlight / shutdown

The inverter transformer high voltage winding has on end connected to the sensing circuits to detect if the lamp are connected or not or if the lamp does not stay on, it is not isolated circuit.
"Also the high pitch noise is present with the monitor off, then it stops when turned on and then heard louder with backlight's attempting to illuminate." OK that is one of the important info. i thought it only squeals when you turn on the monitor.
I would re-cap the board at this point, also check the solder joints, rectifier diodes on the secondary side of the power transformer, etc.

I tested the rectifier diodes and both tested short circuit on the outer two pins of the three. Is that normal? This is in circuit

[budm]

Re: Westinghouse A190E3-H01 no backlight / shutdown

They are Common Cathode dual rectifiers, Center pin is the common Cathode, the two outer pins are Anode, they are connected in parallel (the two Anodes are tied together if look at the traces on the board) to form as one Diode for half wave rectifier circuit.
You can also try heating up the board first with hair dryer for 2~3 minutes and then plug the monitor into the outlet and see if it will function.

[caphair]

Re: Westinghouse A190E3-H01 no backlight / shutdown

I tried heating all the secondary side capacitors with a heat gun for a minute and half, still same symptom.

[caphair]

Re: Westinghouse A190E3-H01 no backlight / shutdown

Recapped secondary side caps, still same hissing noise and symptoms

[budm]

Re: Westinghouse A190E3-H01 no backlight / shutdown

There is a small startup cap (CE107?) in the primary side close to the big power transformer, try that one too.

[budm]

Re: Westinghouse A190E3-H01 no backlight / shutdown

Oh I also forget to ask what DC Voltage you get at the two legs of the main filter cap (120uF 400V) laying on its side.

[caphair]

Re: Westinghouse A190E3-H01 no backlight / shutdown

Oh I also forget to ask what DC Voltage you get at the two legs of the main filter cap (120uF 400V) laying on its side.

I measure 170vdc in standby.

I'm trying to find spare capacitors to replace the little start up one.

Something to note, if I disconnect tcon the quick burst of backlights is way brighter but again same thing, quick flash doesn't stay on.

[caphair]

Re: Westinghouse A190E3-H01 no backlight / shutdown

Changed the start up cap, no change

[caphair]

Re: Westinghouse A190E3-H01 no backlight / shutdown

Ok I think there's an issue with one of the ccfls. I disconnected the pink/white cable one and plugged in the blue/white connector in its place and the screen flashed this. If I leave blue/white connector in place and just unplug pink/white I get no flash of backlights at all but you can see a "no signal" image

[caphair]

Re: Westinghouse A190E3-H01 no backlight / shutdown

Fixed. Turned out to be a bad connection at one of the CCFLs. Carefully soldered and it's up and running!

[budm]

Re: Westinghouse A190E3-H01 no backlight / shutdown

Thanks for the follow-up. So the arcing you were hearing then is from the lamp as I suspected in the beginning of the thread?

[caphair]

Re: Westinghouse A190E3-H01 no backlight / shutdown

Thanks for the follow-up. So the arcing you were hearing then is from the lamp as I suspected in the beginning of the thread?

It didn't sound like arcing just high frequency. I took panel apart and powered it on and the same noise was heard on the return lines from the ccfls so I figured I'd check the connections out and one of the wires just came apart when handling. Resoldered and all is good.

[budm]

Re: Westinghouse A190E3-H01 no backlight / shutdown

If you plan to do more monitors repair, I would suggest you to make at lest two test lamps, it will save so much times on finding out if you have board problems or lamps problems.
This one is really confusing too so make it hard to figure out where the problem is:
"Also the high pitch noise is present with the monitor off, then it stops when turned on and then heard louder with backlight's attempting to illuminate."

[caphair]

Re: Westinghouse A190E3-H01 no backlight / shutdown

If you plan to do more monitors repair, I would suggest you to make at lest two test lamps, it will save so much times on finding out if you have board problems or lamps problems.
This one is really confusing too so make it hard to figure out where the problem is:
"Also the high pitch noise is present with the monitor off, then it stops when turned on and then heard louder with backlight's attempting to illuminate."

Yes I'll have to find some spare lamps for future testing.

Also what's strange is even with it fixed I still can hear the high pitch noise when it's off and then you can hear frequency of lamps while on. So idk about that