Troubleshooting Mag LT865B

[PlainBill]

Re: Troubleshooting Mag LT865B

ok.

I measured voltages on the side of RP2 shown in the enclosed picture. I have labeled the 4 pins coming out of RP2 as 1,2,3,4 (see pic).

1: Is at 5.31V. When i press B2 it goes to 0V.
2: Is at 5.31V. When i press B3 it goes to 0V.
3: Is at 5.31V. When i press B5 it goes to 0V.
4: Is at 5.31V. When i press B4 it goes to 0V.

So does this mean voltages coming into the U7 device are ok and that the U7 device is the problem?

Well, first you have to repeat the test on pins 2-6 of U7. Earlier you had said there was no change on pin 2 when the Power button was pressed. See if every front panel button corresponds to a pin on the MCU. If the signals aren't getting through, it might be a bad solder joint, which could be difficult to fix. If they are getting through then we have to determine if all power supply voltages are present on both U7 and U10.

U7 contains programming. There are two chances of obtaining a properly programmed one - slim and none. As much of a problem that is, replacing U10 would be even worse.

PlainBill

[Welchs101]

Re: Troubleshooting Mag LT865B

Bill, you still there?

[Welchs101]

Re: Troubleshooting Mag LT865B

ok.....i guess thread went to 3rd page..........did not see that.

[Welchs101]

Re: Troubleshooting Mag LT865B

ok....

Button2 (B2) toggles Pin 2 of U7. Pin 2 is at 5.31V and when i press B2 it drops to 0V.

Button3 (B3) toggles Pin 3 of U7. Pin 3 is at 5.31V and when i press B3 it drops to 0V.

Button4 (B4) toggles Pin 5 of U7. Pin 5 is at 5.31V and when i press B4 it drops to 0V.

Button5 (B5) toggles Pin 4 of U7. Pin 4 is at 5.31V and when i press B5 it drops to 0V.

Button1 (B1) toggles Pin 6 of U7. Pin 6 is at 5.31V and when i press B1 it drops to 0V.


So I guess this is good ........right.

What next?

[PlainBill]

Re: Troubleshooting Mag LT865B

ok....

Button2 (B2) toggles Pin 2 of U7. Pin 2 is at 5.31V and when i press B2 it drops to 0V.

Button3 (B3) toggles Pin 3 of U7. Pin 3 is at 5.31V and when i press B3 it drops to 0V.

Button4 (B4) toggles Pin 5 of U7. Pin 5 is at 5.31V and when i press B4 it drops to 0V.

Button5 (B5) toggles Pin 4 of U7. Pin 4 is at 5.31V and when i press B5 it drops to 0V.

Button1 (B1) toggles Pin 6 of U7. Pin 6 is at 5.31V and when i press B1 it drops to 0V.


So I guess this is good ........right.

What next?

Next it gets nasty, ugly, and a PITA. The easy way would be to check the processors and see if there are signs of activity on either of them. If not, start trying to determine why. Possible causes are a dead processor, bad crystal, missing power supplies. Unfortunately, determining if the the crystal is working and if there is any sign of processor activity requires an oscilloscope. Assuming you don't have one on hand, the only thing to do is check the power supplies are all correct.

Here goes. All voltages are DC.

U13, pin 2 should be 3.3V

U1, Pins 2 and 4 should be 3.3V

Check both ends of L6, should be 3.3V

L11 check both ends, should be 5V

TU4, pin 3 should be 9V

L19 Check both ends, should be 3.3V

L22 check both ends , should be 3.3V

TD1, pin 3 should be 2.5V

PlainBill

[Welchs101]

Re: Troubleshooting Mag LT865B

ok. Measured U13.

Pin1: Measured 12.22V
Pin2: Measured 12.22V
Pin3: Measured 12.22V
Pin4: Measured 6.98V
Pin5: Measured 5.34V
Pin6: Measured 5.34V
Pin7: Measured 5.34V
Pin8: Measured 5.34V


I checked schematic on page 26.....U13.......Pins 1,2,3 should be at 12V.

I wonder if we are talking about the same device.

[Welchs101]

Re: Troubleshooting Mag LT865B

U1 measured:

Device: AIC1084(U1)
Pin1: 2.47V
Pin2: 3.73V
Pin3: 5.31V

[Welchs101]

Re: Troubleshooting Mag LT865B

Measured L6: Both sides measure ~ 3.73V

Measured L11: Both sides measure ~ 12.22V

Measured L22: One side measured 3.23V and the other is 3.3V

Measured L19: Both sides measured ~ 3.73V

Measured TD1: Pin3 measured 2.48V


Having trouble locating TU4.........but i will keep looking.

[Welchs101]

Re: Troubleshooting Mag LT865B

Cant seem to locate TU4..........any ideas where i can find it.

[PlainBill]

Re: Troubleshooting Mag LT865B

There is an error on the schematic. Instead of U13, measure the voltage at U12, pin 2. It's next to TC35, which is next to TU4

TU4 is the three legged component next to the power jack. Man, that is one ugly modification hanging off it.

PlainBill

[Welchs101]

Re: Troubleshooting Mag LT865B

U12 measured:
Pin 1: 0.002V
Pin 2: 3.3V
Pin 3: 5.31V



TU4: I have enclosed a pic. I have labeled what i think is TU4 based on what you said. I could not find any writing on the PCB board which said TU4. If this is the right device (TU4) then i measured the voltages as follows:

Pin1: 12.22V
Pin2: 0.01V
Pin3: 9.01V

[PlainBill]

Re: Troubleshooting Mag LT865B

U12 measured:
Pin 1: 0.002V
Pin 2: 3.3V
Pin 3: 5.31V



TU4: I have enclosed a pic. I have labeled what i think is TU4 based on what you said. I could not find any writing on the PCB board which said TU4. If this is the right device (TU4) then i measured the voltages as follows:

Pin1: 12.22V
Pin2: 0.01V
Pin3: 9.01V

Well, I can't think of anything else to try. There is no sign any of the power supplies on the board aren't working. The best conclusion is that either U7 or U10 is bad. Maybe someone else will have an idea.

PlainBill

[Welchs101]

Re: Troubleshooting Mag LT865B

Well, if you cant figure it out Bill then that monitor is probably not going to work again. I know i have tried all i can.

I do really appreciate your help on this......really. You have helped me out not only on this one but others which i am still working on and i really like what you have to say. So thanks.

If you get a moment check out another posting i put up here. I could use your inputs if you have time.

https://www.badcaps.net/forum/showth...3117#post93117


If by some chance someone else does have other inputs on this monitor fix. Please let me know other wise i am going to chuck it in the trash.


Bill, one more question on this monitor. If U10 was bad..........this would not stop the LED from coming on .........right? But U7 would..........right? So my guess is its U7 thats the problem...........what do you think?

[PlainBill]

Re: Troubleshooting Mag LT865B

Well, if you cant figure it out Bill then that monitor is probably not going to work again. I know i have tried all i can.

I do really appreciate your help on this......really. You have helped me out not only on this one but others which i am still working on and i really like what you have to say. So thanks.

If you get a moment check out another posting i put up here. I could use your inputs if you have time.

https://www.badcaps.net/forum/showth...3117#post93117


If by some chance someone else does have other inputs on this monitor fix. Please let me know other wise i am going to chuck it in the trash.


Bill, one more question on this monitor. If U10 was bad..........this would not stop the LED from coming on .........right? But U7 would..........right? So my guess is its U7 thats the problem...........what do you think?

No, you can't make that assumption. U7 accepts key inputs from the front panel and passes them to U10. U10 takes the VGA information from the computer, processes it and passes it to the LCD display panel. It also takes information from U7 and uses it to modify the information sent to the LCD panel. For example, if you hit the Menu button, U10 brings up the OSD. Information is also passed to from U10 to U7. For example, if the computer is shut down, U10 passes a command to U7 to turn the power LED from green to orange.

I wouldn't throw the monitor away, I'd suggest listing it on one of the free advertising services (Freecycle, Craigslist) so possibly someone else can use whatever arts of it they desire. For all we know, the is some guy with one of these sitting in a closet because he got mad and threw a mouse at the screen.

PlainBill

[Welchs101]

Re: Troubleshooting Mag LT865B

Will do.

[Welchs101]

Re: Troubleshooting Mag LT865B

Thanks for your help on this one bill. Looks like no one else has any ideas so i will end work on this monitor.

FYI: I like to tinker.....learning alot the last year since i am unemployed. Some how i fixed a few things for friends and neighbors and now i am getting a few items every month or so to fix. Keeps me busy. So this is why you probably see me on here a lot lately. Thanks again for your help.