Need help with my 900G

[retiredcaps]

Re: Need help with my 900G

I decided to hook the monitor up to my computer since it was acting more like it used to with the power light.
When I connect it to my PC and turn it on the light stays blue, sorry not green, and when I put a flashlight next to the screen I can see a rectangular screen saver running with some test on it that I can't read.

In post #9, I thought you had a source (aka computer) hooked up to the LCD.

Try this. Boot a computer with a good working monitor running windows or linux. Bring up a web browser and goto www.badcaps.net. Now move the video cable from the working monitor to the 900G. If you shine the flashlight on the 900G, do you see the web browser?

If yes, then this suggests that your mosfets are possibly shorted. To test them, look at the mosfet part number. They should be labeled right on the chip.

Search for the mosfet datasheet. Once you find the datasheet, it will tell you which pins are source, gate, and drain.

You want to test the resistance (ohms) between source and gate (S-G), source and drain (S-D), and finally drain and gate (D-G).

Any ohms reading less than 20 ohms suggests a short. However, since these mosfets are tested "in circuit", you will need to desolder them and test them "out of circuit" IF the "in circuit" tests suggest they are shorted.

[oldmanjohnson]

Re: Need help with my 900G

Okay I checked the red circle on the right, which is a fuse, but the red circle on the left is a resistor.
I also checked all the fuses on that board and they check good.

[oldmanjohnson]

Re: Need help with my 900G

I'm sorry I thought I could just plug in the monitor turn it on and if it was working I would at least get the missing video message. So all this time that was what I was looking for as I worked on it on the bench. I did try hooking it up a couple of times but it was always the same as on the bench.
Also I did hit the reset button on the computer while it was attached and I didn't even get the DOS screen. The whole time it was showing that rectangle moving around like a screen saver.
Should I still test the mosfets?

[Wrog]

Re: Need help with my 900G

Definitely check the mosfets.

[oldmanjohnson]

Re: Need help with my 900G

Okay I checked the mosfets on board and I had to set the meter to 20m to get a reading. So I took one of them off the board and got the same results. I decided to just go ahead and order the mosfets and the ccfl chip. Figured for what they cost I might as well change them and see if that solves the problem.

[oldmanjohnson]

Re: Need help with my 900G

Here's the latest info with my 900G headache.
I replaced the mosfets and the ccfl chip and I'm still not getting the lamps to fire. With it hooked up to my laptop I can see the screen with a flashlight which it was doing before I changed the chips. I have checked all fuses on each of the circuit boards and all check good with my volt ohm meter set to diode test with sound.
How should I proceed from here?

[oldmanjohnson]

Re: Need help with my 900G

Here's the latest info with my 900G headache.
I replaced the mosfets and the ccfl chip and I'm still not getting the lamps to fire. With it hooked up to my laptop I can see the screen with a flashlight which it was doing before I changed the chips. I have checked all fuses on each of the circuit boards and all check good with my volt ohm meter set to diode test with sound.
How should I proceed from here?

[PlainBill]

Re: Need help with my 900G

Here's the latest info with my 900G headache.
I replaced the mosfets and the ccfl chip and I'm still not getting the lamps to fire. With it hooked up to my laptop I can see the screen with a flashlight which it was doing before I changed the chips. I have checked all fuses on each of the circuit boards and all check good with my volt ohm meter set to diode test with sound.
How should I proceed from here?

Two pieces of information for you:

1. We have to make sure the inverter is getting power.
2. We have to make sure the control signals are getting to the inverter controller.

Two pieces of information I need from you:

1. A GOOD picture of the back side of the inverter. Note the links in my signature. This should be as close to 2000 x 2000 as practical. I have to be able to trace circuits and identify components on the board.
2. The part number of the inverter controller.

PlainBill

[alexanna]

Re: Need help with my 900G

I'm sorry I thought I could just plug in the monitor turn it on and if it was working I would at least get the missing video message. So all this time that was what I was looking for as I worked on it on the bench. I did try hooking it up a couple of times but it was always the same as on the bench.
Also I did hit the reset button on the computer while it was attached and I didn't even get the DOS screen. The whole time it was showing that rectangle moving around like a screen saver.
Should I still test the mosfets?

I am reading a little bit between the lines, Could the rectangle box that's floating around be saying no signal?
Al.

[oldmanjohnson]

Re: Need help with my 900G

I wondered about that myself but kept watching it until I saw the word windows in the box. Also when I turn it on, and it's connected to my laptop, the power light turns on blue for 10 seconds and then turns yellow. Then when I press the keys to shift the video to the external monitor, the monitor immediately turns the power light blue and stays that way until I exit external monitor mode.

[alexanna]

Re: Need help with my 900G

I wondered about that myself but kept watching it until I saw the word windows in the box. Also when I turn it on, and it's connected to my laptop, the power light turns on blue for 10 seconds and then turns yellow. Then when I press the keys to shift the video to the external monitor, the monitor immediately turns the power light blue and stays that way until I exit external monitor mode.

Just checking.
Please follow PlainBill's reguests.
Al.

[oldmanjohnson]

Re: Need help with my 900G

Plain Bill
okay this is the best image I could get out of my camera with my 50 yr old nerves.
When you say, "the inverter controller", are you referring to the ccfl chip? If so that number is BIT3193G.

[PlainBill]

Re: Need help with my 900G

Plain Bill
okay this is the best image I could get out of my camera with my 50 yr old nerves.
When you say, "the inverter controller", are you referring to the ccfl chip? If so that number is BIT3193G.

When you say "ccfl chip" do you mean the inverter controller?

I've marked up the picture you uploaded. It turns out I already had one from another thread. Yours is much better. Some points to check

Red circle - check for short across that gap.

Check the following points with power on and signal applied, power LED on

Blue circle (voltage for inverter) - what is the voltage across that cap?
Yellow circles A and B (On / off and brightness). What are the voltages at these points with power LED on? With Power LED off?

Inverter controller - What is the voltage on pin 6 (inverter on/off) and pin 10 (Vdd).

PlainBill

[oldmanjohnson]

Re: Need help with my 900G

Plain Bill
I checked all that you requested and marked the board.
You will notice that I accidentally put a yellow dot on pin 9 but please note I dropped the dot early and my eyesight deceived me. My voltage checks were in fact on pin 6 and pin 10 as requested.
The cap in the blue circle isn't showing any voltage on the one side on or off. Is replacing that as simple as finding one of the same color on another circuit board? I have no idea what the rating is and I don't have a schematic. I ordered one from schematics dot me and it wasn't the correct component boards. So they refunded my money.

[PlainBill]

Re: Need help with my 900G

Plain Bill
I checked all that you requested and marked the board.
You will notice that I accidentally put a yellow dot on pin 9 but please note I dropped the dot early and my eyesight deceived me. My voltage checks were in fact on pin 6 and pin 10 as requested.
The cap in the blue circle isn't showing any voltage on the one side on or off. Is replacing that as simple as finding one of the same color on another circuit board? I have no idea what the rating is and I don't have a schematic. I ordered one from schematics dot me and it wasn't the correct component boards. So they refunded my money.

We're making progress. Sorry, I didn't give you a good explanation of what I was looking for. The cap circled in blue is a decoupling cap. I expected to see about 12 Volts across it. The voltages you got indicate power is getting to the inverter circuitry.

The suspected solder short of course is non-existent. That's good.

The two points I circled in yellow are significant. A is On/off, B is brightness, the voltages are reasonable.

The other significant readings are pins 6 and 10. They should be at about 5V when the inverter is on.

I've attached a schematic that is SIMILAR to the circuit we are dealing with. Note the signal that comes in on J1, pin 4. It goes through Q2, Q3, and Q1. Also note D1, the zener diode, which limits the voltage to the inverter controller.

I use an 'arm waving' approach to analyzing these circuits. If pin 4 is high Q2 is turned on, so it's output is low, and Q3 is turned on. This pulls the output of Q3 high until D1 begins to conduct. The lower pin of Q1 should be about .7 volts below the voltage at the anode (top) of the zener diode.

On your board the cylindrical banded component above and slightly to the right of the BIT3193 is the zener. If that is shorted, it would cause the problem you are seeing. You should be able to trace from point A to pin 10 of the BIT3193.

PlainBill

[oldmanjohnson]

Re: Need help with my 900G

PlainBill
Thank you for all the great info especially the schematic.
I checked the zener diode off board and with my volt meter set to diode test, with sound, I get continuous noise in both directions. Does that mean it's bad? Also how do I decipher the color bands on the diode? Green, green, brown.

[PlainBill]

Re: Need help with my 900G

PlainBill
Thank you for all the great info especially the schematic.
I checked the zener diode off board and with my volt meter set to diode test, with sound, I get continuous noise in both directions. Does that mean it's bad? Also how do I decipher the color bands on the diode? Green, green, brown.

You will have to remove it from the circuit to be sure it is bad. If it reads shorted (less than 1 ohm) I would replace it. I'm not sure how to read the marking bands. Try googling smd diode color bands

PlainBill

[PlainBill]

Re: Need help with my 900G

OK, I got it. According to one reference, that is actually brown green, green, and corresponds to a 7.5V zener, which agrees with the value shown in the schematic I attached earlier.

PlainBill

[oldmanjohnson]

Re: Need help with my 900G

PlainBill
well I replaced the defective zener, brown green green, with the only one I could find, red red green, attached to one of my used circuit boards.
I am typing this post using the monitor that has been down for weeks.
THANK YOU, THANK YOU, THANK YOU and to all the others that worked patiently with me through this.
Now I just need to figure out why I have a horizontal line across the middle of the screen. Go figure. LOL
Do you have any ideas what could be causing this? Is it because I used a different zener?

[oldmanjohnson]

Re: Need help with my 900G

Hey the line went away.
I got up this morning and played a little free cell. Went online to see if there was a reply to the previous post and while I was looking for some info the horizontal line just disappeared.
Any reason for me to be concerned? Does anyone know what caused it?