Visio VO370m - 1 second backlight

[ahickman]

Just got a Visio VO370m that powers on (visio symbol goes from amber to white) and the backlights come on for 1-2 seconds. Set responds to the PWR button, turning off. All fuses check OK. Visually inspected capacitors, nothing apparent. Resoldered all the pins of the inverters and transformers. Getting ready to measure voltages on all regulators.

[drpj23]

Re: Visio VO370m - 1 second backlight

Is there an image on the screen although backlights are off?

[ahickman]

Re: Visio VO370m - 1 second backlight

Power supply cap (C4) = 394 VDC
U11 (7805 reg.) = 5.03 VDC
T-con had 11.97 VDC on both sides of the fuse

U8
0 VDC (adj)
1.25 VDC (out)
3.26 VDC (in)

U2
2.04
3.28
4.95

U5
1.37
2.61
4.95

U4
2.05
3.30
4.99

U9
1.25
2.50
4.95

[ahickman]

Re: Visio VO370m - 1 second backlight

Yes, there are images when i shine a light. Inverter board?

[Mt.Man]

Re: Visio VO370m - 1 second backlight

Shine a bright light on the screen after the back lights cut off. If you can see video then the problem is either the inverter side of the power board is shutting down, or a bad lamp in the panel is causing the inverter to shut down.

[budm]

Re: Visio VO370m - 1 second backlight

How are those small blue ballast caps on the output side of the inverter transformers/ Do they look like it has some brownish color to the body. Transformer resistance checking will be next.

[retiredcaps]

Re: Visio VO370m - 1 second backlight

Your photo is quite clear enough and I don't have selldoor's eyesight, but this may be your transformer that budm alluded to

http://www.lcdparts.net/TransformerD...ProductID=2796

Measure and report the resistance between S1-S2 and S3-S4 for all of them

[ahickman]

Re: Visio VO370m - 1 second backlight

The xformer you found does not match the pinouts for the transformer on the board. Below are more detailed pictures of the front/back. I searched for the replacement part, but was unable to find a pinout. Going to desolder one of them now.

[selldoor]

Re: Visio VO370m - 1 second backlight

Its always difficult when you cant find the exact part number and just have to go by something near - i couldnt find it either.
You need to do the long test ( which actually takes longer to type than to do.)
Draw a rough pic and number the pins 1 to 9 or whatever - Power OFF Meter on 2000 ohms test pin1>pin2 Pin1 > pin3 Pin 1>Pin4 and so on then Pin2>pin3 pin2 >pin3 Pin2>pin4 to pin 2 >pin9 then pin3 >pin4 pin 3 >pin5 etc etc At some point you will get something in the range 600 to 1200 ohms make a note of those pins and check the same pins on the other transformer. and report results
( Only the high numbers)

Looks like the secondaries are on the side nearest the edge of the board but you cant always tell.

[budm]

Re: Visio VO370m - 1 second backlight

When you remove the transformer an look at the bottom side then it will be easier to figure out.

[ahickman]

Re: Visio VO370m - 1 second backlight

Hope this diagram make sense. Looks like a single primary with 13 ohm resistance and two separate secondary turnings with ~1.8K ohms resistance.

[ahickman]

Re: Visio VO370m - 1 second backlight

Budm, what is the best way to test the blue caps. I have an ESR meter, but don't know if the mylar type respond.

[selldoor]

Re: Visio VO370m - 1 second backlight

That would do it! now check the other transformers - results should be within 3%

[tom66]

Re: Visio VO370m - 1 second backlight

ESR won't work for picofarad caps, unless you have an LCR meter.

[budm]

Re: Visio VO370m - 1 second backlight

Those ballast caps when they go bad it will have leakage resistance from 10K to 200K, good cap will show open circuit. Just set your meter to highest resistance scale and tak the reading, just do not touch the two probes with you fingers otherwise you will be reading your body resistance.
Your VO370M does not look anything like the one I worked on a few weeks ago.
http://s807.photobucket.com/albums/y...izio%20VO370M/

[ahickman]

Re: Visio VO370m - 1 second backlight

All primary windings are 12 ohms. All but one transformer have secondary windings close to 1760 ohms. One transformer has secondaries that read 1696 and 1820 ohms.

[tom66]

Re: Visio VO370m - 1 second backlight

The 1820 ohms is suspicious, but it is only 3.5% out. Although the rule is 3%, it is so close to be hard to tell.

[selldoor]

Re: Visio VO370m - 1 second backlight

ok the one off the board just passes the last one with 1696 is a fail. now to find a new one -as i say i could read the number but could not find one. You may have to try and find a whole board - even a faulty one should have at least one transformer that is good.

[ahickman]

Re: Visio VO370m - 1 second backlight

Thanks Selldoor. Looking for a replacement now.

[retiredcaps]

Re: Visio VO370m - 1 second backlight

http://www.ebay.com/itm/130757248772