Mag 780 LT776S Not working....cap question on inverterboard

[Welchs101]

Re: Mag 780 LT776S Not working....cap question on inverterboard

How do i test the inverter? I have an extra computer power supply.......

What exactly do i do?

[seanc]

Re: Mag 780 LT776S Not working....cap question on inverterboard

Yellow is 12v, Red is 5v. Chop and solder...

[Welchs101]

Re: Mag 780 LT776S Not working....cap question on inverterboard

ok....so yellow is 12V and red is 5V.

So i just hook up those wires to the inverter and then what? I assume i plug in the lamps and if the lamps light up then the inverter is ok.......is this right?

[Welchs101]

Re: Mag 780 LT776S Not working....cap question on inverterboard

Does anyone know if my previous post is sufficient to test the inverter?

[Welchs101]

Re: Mag 780 LT776S Not working....cap question on inverterboard

So, if i hook up the 5V and 12V from computer power supply to my inverter from the LCD..........will i hurt anything?

If there is a problem in the inverter..........will the power supply simply shut down or will it "catch fire"........ie...are there protection circuits in the power supply to turn it self off if the inverter is drawing a lot of current?

Does any one know?

[PlainBill]

Re: Mag 780 LT776S Not working....cap question on inverterboard

So, if i hook up the 5V and 12V from computer power supply to my inverter from the LCD..........will i hurt anything?

If there is a problem in the inverter..........will the power supply simply shut down or will it "catch fire"........ie...are there protection circuits in the power supply to turn it self off if the inverter is drawing a lot of current?

Does any one know?

More likely if there is a problem with the inverter, it will go up like a torch. They don't draw too much current - probably something like 1 amp. Whereas the computer power supply I just looked at puts out 18 amps at 12 Volts.

PlainBill

[sofTest]

Re: Mag 780 LT776S Not working....cap question on inverterboard

I'm not en EE, but according to all information on the subject I've seen, amps are drawn on, not "put out", to be correct. Anyway, if there is a problem with the inverter, PlainBill is correct. Some kind of current limiting might be wise.

[seanc]

Re: Mag 780 LT776S Not working....cap question on inverterboard

I think PlainBill was implying 'can put out'/'can be drawn'.

[PlainBill]

Re: Mag 780 LT776S Not working....cap question on inverterboard

I think PlainBill was implying 'can put out'/'can be drawn'.

Sorry, my mind was in the gutter; that's why I used 'put out'. A more appropriate term is 'has available'.

Welchs101, you can hook an inverter up to any 12 volt power supply, even one capable of putting out 400 amps - like a car battery. But if there is a problem, the safety features in that power supply will not protect the inverter.

Fortunately, unlike in the Seaview in 'Voyage to the Bottom of the Sea', there are devices available called 'fuses'.

PlainBill

[Welchs101]

Re: Mag 780 LT776S Not working....cap question on inverterboard

Would the fuse located on the inverter board itself be enough to protect it.

Just not sure what to do now.

The monitor will come one for about 2 seconds. I feel like i am so close to fixing it but just cant figure it out.

Any one have any ideas?

[PlainBill]

Re: Mag 780 LT776S Not working....cap question on inverterboard

Would the fuse located on the inverter board itself be enough to protect it.

Yes, provided it has one.

Just not sure what to do now.

The monitor will come one for about 2 seconds. I feel like i am so close to fixing it but just cant figure it out.

Any one have any ideas?

Yes, you have the 'two seconds to black' problem. I have REPEATEDLY discussed the causes of the problem, and the steps to troubleshoot it. Maybe someday before I burn out I will post a step by step analysis of a failure, but not in the next two months.

Search on my posts on the subject. If you can't figure out what points to measure, post good pictures (front and back) of the inverter.

PlainBill

[Welchs101]

Re: Mag 780 LT776S Not working....cap question on inverterboard

Bill,

I searched on your name and the words "seconds to black" and found several comments you made.

From what i can tell you want me to do the following:
1-Measure secondary resistances of transformer (on inverter board). I have enclosed a pic as reference. So i measure A-B and C-D.

2-Also you want me to hook up everything (including ccfl bulbs) and measure from Vgnd to Vreturn of the lamp (again see enclosed pic). Note: I have 4 lamps in this LCD. I have 4 "hot" wires but only "2" return wires. So, the bulbs are shorted together for the return.....thus why i have only 2 return wires.

Question: Measuring the "Vgnd to Vreturn voltages.......i read somewhere that this voltage would be very high and could harm my DMM........is this true? Or is this only if i measure from Vgnd to Vhot............



Also, i have included photos of the front and back of the inverter board.

[Welchs101]

Re: Mag 780 LT776S Not working....cap question on inverterboard

I measured the resistance
A-to-B: 0.2ohm

C-to-D: 0.2ohm


I will measure the Vgnd to Vreturn voltages once i get a response on my question from my previous post.

[PlainBill]

Re: Mag 780 LT776S Not working....cap question on inverterboard

I measured the resistance
A-to-B: 0.2ohm

C-to-D: 0.2ohm


I will measure the Vgnd to Vreturn voltages once i get a response on my question from my previous post.

Something isn't right about the resistance. I'd expect something around 1K ohms.

The return voltage should be less than 10 volts. The output voltage could be as high as 1000 volts.

PlainBill

[Welchs101]

Re: Mag 780 LT776S Not working....cap question on inverterboard

I am enclosing a pic of how i measured the 0.2ohms........am i measuring across the right terminals?

[PlainBill]

Re: Mag 780 LT776S Not working....cap question on inverterboard

I am enclosing a pic of how i measured the 0.2ohms........am i measuring across the right terminals?

You appear to be. How about a close up of the end of that area.

PlainBill

[Welchs101]

Re: Mag 780 LT776S Not working....cap question on inverterboard

Here is a close up of that end....let me know if i can provide more info.

[PlainBill]

Re: Mag 780 LT776S Not working....cap question on inverterboard

Here is a close up of that end....let me know if i can provide more info.

The black arrows point to the output terminal. The red circle MAY be the other end of the secondary. Or there are 7 terminals at the other end of the transformer. One of them may be the other end of the secondary.

I've identified the return test points.

PlainBill

[Welchs101]

Re: Mag 780 LT776S Not working....cap question on inverterboard

Bill,

When i measure the resistance between the black arrow terminals and the red circle i get an "open"....for both transformers. I am not even sure the "small" terminal is soldered to anything.

I tried to look up the transformer (see pic.....it has part number) but nothing really came up.

I will measure voltages and send in my next post.

[PlainBill]

Re: Mag 780 LT776S Not working....cap question on inverterboard

Bill,

When i measure the resistance between the black arrow terminals and the red circle i get an "open"....for both transformers. I am not even sure the "small" terminal is soldered to anything.

I tried to look up the transformer (see pic.....it has part number) but nothing really came up.

I will measure voltages and send in my next post.

Welchs, check the resistance from the output terminal to each of the 7 terminals on the other end of the transformer. One of them should be the other end of the transformer secondary.

PlainBill