Mag 780 LT1776s not working then works then not

[ubuntubill]

Black sreen when on w blinking power light. No functions from Menu.

So, I disassembled it & saw no visible defects. Reassembled & read voltages at inverter connection w vga connected & PC on:

Connector voltages:
Pin1: 0V DC
Pin2: 0V DC
Pin3: 2.68V DC
Pin4: 3.67V DC
Pin5: 12.0V DC
Pin6(red): 12.0V DC

Viola! The monitor works again. Upon reassembly, black sreen when on w blinking power light. No functions from Menu.

Connector voltages:
Pin1: 0V DC
Pin2: 0V DC
Pin3: 2.69V DC
Pin4: 0V DC
Pin5: 12.21V DC
Pin6(red): 12.21V DC

Any suggestions on where to start?

[ubuntubill]

Re: Mag 780 LT1776s not working then works then not

Can a schematic of the main board for the circuit to the lead for #4 pin be provided?

[Agent24]

Re: Mag 780 LT1776s not working then works then not

Is there any labelling on the board next to pin 4 to indicate what it may do?

A quick look online doesn't turn up any schematic. But sometimes the boards are re-used in multiple brands\models. If you post the board numbers we might get lucky.

You might also want to check for bad solder joints around the connecting cables and on the board in general. If it randomly works and doesn't work, a loose connection somewhere is a high possibility.

[budm]

Re: Mag 780 LT1776s not working then works then not

Pin 3 and pin 4: One of them is for backlights dimming control signal, another one is for the BL_ON signal which will be present when it detect the VIDEO signal from the PC.
You can verify pin 4 when the monitor is apart and see if it goes high when it is connected to the PC and goes low when the PC is disconnect (the monitor goes into standby so the backlights are turned off), you may have to wait a few minutes after the PC is disconnected.

[ubuntubill]

Re: Mag 780 LT1776s not working then works then not

inverter board #'s
MPT
M074
849-40M-0770

Main board #'s
HI4-04
022686

Pin 4 0v in all situtations.

[ubuntubill]

Re: Mag 780 LT1776s not working then works then not

Here's a photo fo the main board & it's numbers:

[selldoor]

Re: Mag 780 LT1776s not working then works then not

Please post pictures using manage attachments so they remain with the forum for future use - I have added these to this post

[Neelix]

Re: Mag 780 LT1776s not working then works then not

Number on main board is 200-100-SH770 rev 4. Attached is a service manual for the Proview 770 with circuit diagrams, etc. for the same main board. Don't know if the inverter board is also the same because I can't see the numbers on the inverter board in the photos

[ubuntubill]

Re: Mag 780 LT1776s not working then works then not

Is U2 pin 2 the 2nd pin clockwise from the two 45 degree angled corner?

[Agent24]

Re: Mag 780 LT1776s not working then works then not

If U2 the SyncMOS SM89516C25J, then no.

PLCC parts usually start with Pin 1 in the center of one side (indicated with a dot) - in this case just above the 'M' in SyncMOS. Pin 2 will be the next pin to the left, and Pin 44 will be the next pin to the right of Pin 1.

See the attached datasheet, page 2, for the pinout.