Viewsonic VT3745 powering up issues

[Midnightalaskan]

Re: Viewsonic VT3745 powering up issues

Yep! 24v on both side of F1 and 2

This is why I'm so dang confused! Everything I have poked at says it should be on.

[budm]

Re: Viewsonic VT3745 powering up issues

I just updated my previous, please read it again.

[Midnightalaskan]

Re: Viewsonic VT3745 powering up issues

Just caught that. Nothing on that grey wire I_PWM

Yah it's like I have to keep trying until it decides we are worthy enough to watch a movie.

It works... Kind of... But not to spec.

[budm]

Re: Viewsonic VT3745 powering up issues

Try removing that I_PWM line or cut the wire long enough so you can splice it back together later on and see if the backlights will come on.

[Midnightalaskan]

Re: Viewsonic VT3745 powering up issues

Cut the wire and nothing changed. No backlight.
Standby light still does it's off on off thing too. All voltage at the PSB (5,12 and 24v) look fine when trying to power on.

[Midnightalaskan]

Re: Viewsonic VT3745 powering up issues

Just got home and did a little probing (to the tv not the wife ) after cutting the I_pwm it seems I have lost my ground through the metal frame of the LCD display. When I ground to the frame and volt tick everything on the PSB, inverter board and main board I get around 1.5v on my meter on everything. If I ground it to the ground stud on the PSB, everything shows correct voltage. Just as a recap with the unit "on" I get the following out of the PSB

Going to the main board:
Acd 3.4v. P_on 2.8v
3-5v posts 4.99v. 3-GDN post grounded
3-12v post 11.99v. BL grounded
GND grounded. BRI grounded
PWM 0.005v

Now the plug going to the inverter board

BL grounded. BRI grounded
4-GND grounded. N.C. Nothing
4- 24v. 24.60v.

Those readings are from the PSB and when I ground it on the PSB

Like I stated... Most all the plugs register 1.5v when trying to ground through the LCD metal frame.

Now here's something odd... I slipped while probing the main board and accidentally put my probe between the BL and 12+ post and the backlight turned on.... I removed it as quickly as I had set it there... But it definitely turned on the ccfl. I did it once more for a nano second to confirm I wasn't seeing things... Since the LCD screen is on the floor face down, it's hard to tell if the unit is actually on(the ccfl is on but I don't know if the tv is functioning). I don't want to hold the probe there too long just in case it's bad that I "jumped" the connection. All this is while the tv has stalled on the blue light (on) not while on standby.

Now I'm confused...

[budm]

Re: Viewsonic VT3745 powering up issues

OK, on post 15 you did have DC voltage at BL pin, and now you do not.
But the main key right now is that you are able to force on the backlights buy applying 12V to BL line. When we test the inverter board we use 1K resistor between BL (or BL_ON) and the 5VSTBY pin to force on the backlights.
So it is telling me that your main board is not sending the BL signal to turn on the backlights. So I would use the 1K as I mention, once you can see the backlights, if the main board other functions are OK, you should then be able to see the images on the screen, if not, then your main board is more likely to be the problem.

[Midnightalaskan]

Re: Viewsonic VT3745 powering up issues

Should I repair the PWM grey wire I cut first?

[budm]

Re: Viewsonic VT3745 powering up issues

Yes, reconnect that wire. I have a feeling that the backlights will not come now even when you apply the voltage to the BL pin.

[Midnightalaskan]

Re: Viewsonic VT3745 powering up issues

Wire reconnected, used a 1k resistor between 5v and BL on the main board... After successfully shocking myself, I was not able to get the backlight to come on unless I put the probe between the 12v and BL as explained above.

I just did the 12v to BL for a second and I do not see the tv working when the ccfl is on. In fact it is only on when the the standby light is blue but shuts off when it goes back to orange. Something keeps kicking it back to standby (orange light).

Ok after 100 tries of the power button I got it to kick on and run... Now volt ticking I show at the PSB going to the main board:
ACD 3.37v. P_on. 2.798v
3-5v posts 4.96v 3-GDN posts. Grounded
3-12 posts 12.08v. BL. 4.86v
GND grounded. BRI 2.38v
PWM 0.05v
I get the same V at the main board plug as well

From the PSB to the inverter board
BL 4.86v. BRI 2.888
PWM. 0.43v. 4-GND posts grounded
4-24v posts 24.28v
I get the same V on the inverter board plug as well.

I can now get a ground through the LCD panel frame as well (where it wasn't reading last time)
The ground is also working through corresponding grounds on the PSB inverter and main board.

If I shut it off, it's back to square one with the not turning on.

[Midnightalaskan]

Re: Viewsonic VT3745 powering up issues

After some extensive searching.... I only found one main board online for $100... Used and off ebay. I'm hoping it's not the MB but if it is, can the MB be repaired to a point?

[Midnightalaskan]

Re: Viewsonic VT3745 powering up issues

Any suggestions about what to try next?

[budm]

Re: Viewsonic VT3745 powering up issues

Main board repair is not easy, sometime it can be simple bad voltage regulator. $100 for main board is really expensive for 37" screen, $50 for the most I would spend on main board for 37" TV. At this point we know that the backlights and the power supply are OK, but the main board is not functioning properly.

[Midnightalaskan]

Re: Viewsonic VT3745 powering up issues

Damn! So just volt tick stuff untill I find a problem or find a new mb? Well at least it kinda works... I better get it back together before the wife kills me!

[Midnightalaskan]

Re: Viewsonic VT3745 powering up issues

Are there places that I could send the MB off to to get fixed? After a bunch of searching, I cant find a MB anywhere!

Also Thank you very much for all the help Budm you rock!

[doggs]

Re: Viewsonic VT3745 powering up issues

Hi guys, thank you for all the info.