CTX S762G - Some Questions...

[pantherts]

Re: CTX S762G - Some Questions...

Thank you for replying. Ah, well then. So PlainBill, do you think that this could be causing the issues I'm having? Following the traces it seems that that item is in direct contact with the plug that goes to the video board. This makes me think that it could be causing problems between the video board and the power board. (The OFF signal for the lamps when the power button is pressed and the on signal to power up the video board itself) You think this sounds feasible?

Also, I'm one step ahead of you on that. I already removed the transistor and I did measure resistance but I don't have the information here at work. I will write again when I get home with the info.

[pantherts]

Re: CTX S762G - Some Questions...

Okay, here are my results for testing the resistance for the transistor. P=Positive Lead, N=Negative Lead, E=Emitter, C=Collector, B=Base.

P---N

E to C - OL

E to B - OL

C to E - OL

C to B - OL

B to E - 1.645

B to C - 1.624

So looking at that, I'm guessing something is amiss?

[PlainBill]

Re: CTX S762G - Some Questions...

Okay, here are my results for testing the resistance for the transistor. P=Positive Lead, N=Negative Lead, E=Emitter, C=Collector, B=Base.

P---N

E to C - OL

E to B - OL

C to E - OL

C to B - OL

B to E - 1.645

B to C - 1.624

So looking at that, I'm guessing something is amiss?

Arghh!!! I'm getting old, this used to be second nature. IF the shattered remnants of my mind are still working AND those are the resistance readings (not voltage drop on a diode test scale), that looks like a perfectly good transistor.

PlainBill

[pantherts]

Re: CTX S762G - Some Questions...

Okay, assuming that transistor is fine. I'm going to start tracing back from that transistor I guess (since that is where the short occurred). Anything in particular I should be looking for?

[PlainBill]

Re: CTX S762G - Some Questions...

Okay, assuming that transistor is fine. I'm going to start tracing back from that transistor I guess (since that is where the short occurred). Anything in particular I should be looking for?

OK, I just reviewed the entire thread and am more confused than ever. Let's take a few steps back and attack this logically.

First, very close to the AC connector is a large capacitor mounted horizontally. With the AC power on, CAREFULLY measure the voltage across that cap. It should be in the 160-180 volt range, definitely enough voltage to sting.

Second, in the upper left corner of the picture labeled 'Top 1' a multicolored cable is shown. I believe it's connector is P2. Are there any labels on the board indicating what each lead carries? (Something like GND, 5V, 12V, etc?). If those marking are there, could you measure the voltages.

Third, would you mark up a copy of 'Top 1' indicating which capacitors were replaced.

PlainBill

[pantherts]

Re: CTX S762G - Some Questions...

PlainBill, I must thank you for helping me with this. I really appreciate it. I'm sorry that I'm a bit wet behind the ears with all of this but I'm treating this little project as a learning experience. I find working on electronics a lot of fun and it's starting to become a hobby of mine because of all of this.

Okay, I'm currently at work but I will update this thread with the requested information when I get home tonight. The multicolored cable (the one that goes to the video logic board) I'm pretty sure does not have any markings on it which is not very helpful. I will take the voltages though and put them all in my post. Thanks!

[PlainBill]

Re: CTX S762G - Some Questions...

PlainBill, I must thank you for helping me with this. I really appreciate it. I'm sorry that I'm a bit wet behind the ears with all of this but I'm treating this little project as a learning experience. I find working on electronics a lot of fun and it's starting to become a hobby of mine because of all of this.

Okay, I'm currently at work but I will update this thread with the requested information when I get home tonight. The multicolored cable (the one that goes to the video logic board) I'm pretty sure does not have any markings on it which is not very helpful. I will take the voltages though and put them all in my post. Thanks!

No problem. I've dealt with many different types; the 'has a lot to learn, but is eager to learn' is my second favorite type. (The 'has a lot to teach and is willing to teach me' is number 1!!)

PlainBill

[pantherts]

Re: CTX S762G - Some Questions...

PlainBill,

Okay, here we go:

1) Large capacitor is reading 164.4 volts
2)Connector P2 is as follows (no markings):
Black: 0v
Brown: Climbs slowly from 0 to ???
Red: 12.23v
Orange: 0v
Yellow: 0
Green: 3.319v
Blue: 3.319v
Purple: 4.88v
Gray: 4.88v
White: 0v
White: 0v

3) All capacitors have been replaced on the board except for the largest capacitor which you had me measure.

Okay, also. I plugged it all in and here's some more info. The backlight comes on immediately (without having to press the power button). When I press the power button the green LED comes on but nothing is on the screen. Backlight still is lit. I noticed that the logic board's processor(?) gets extremely hot very quickly. It is a Genesis gm5120 chip. Not sure if this is normal or not. When power button is pressed again, green LED goes off but backlight stays lit. At this point I have not plugged in a video source because I'm 99% sure that a "No video source detected" message should be popping up. I'm thinking that somehow the logic board is not turning on or something?

[pantherts]

Re: CTX S762G - Some Questions...

New Pictures of Bottom of board:

Bottom View 4

Bottom View 5

Bottom View 6

Hopefully these will help. They should be a bit clearer than the first ones I uploaded. Less artifacts anyways. And yes I know it looks a bit messy, darn flux gets everywhere. C17 kinda appears weird in the photo but pretty sure that cap is fine (it's one of the new Panasonics).

[PlainBill]

Re: CTX S762G - Some Questions...

PlainBill,

Okay, here we go:

1) Large capacitor is reading 164.4 volts
2)Connector P2 is as follows (no markings):
Black: 0v
Brown: Climbs slowly from 0 to ???
Red: 12.23v
Orange: 0v
Yellow: 0
Green: 3.319v
Blue: 3.319v
Purple: 4.88v
Gray: 4.88v
White: 0v
White: 0v

3) All capacitors have been replaced on the board except for the largest capacitor which you had me measure.

Okay, also. I plugged it all in and here's some more info. The backlight comes on immediately (without having to press the power button). When I press the power button the green LED comes on but nothing is on the screen. Backlight still is lit. I noticed that the logic board's processor(?) gets extremely hot very quickly. It is a Genesis gm5120 chip. Not sure if this is normal or not. When power button is pressed again, green LED goes off but backlight stays lit. At this point I have not plugged in a video source because I'm 99% sure that a "No video source detected" message should be popping up. I'm thinking that somehow the logic board is not turning on or something?

The logic board's processor may get warm, but I wouldn't expect it to get 'extremely' hot. That is not a good sign. About the only suggestions I have at this point is see if you can find an identical monitor which you can salvage for parts, or can find information on the logic board.

PlainBill

[pantherts]

Re: CTX S762G - Some Questions...

Well that's not good. I really wish I knew the values of that P2 connector. That may help me in my diagnosis of what's going on here. Unfortunately, we don't have another other monitors of this exact same model at my office. We do have other CTX monitors but all of them are of a different model number.

[pantherts]

Re: CTX S762G - Some Questions...

So I did some further testing. I unplugged the video logic board from the power board and plugged it in. The backlight did not come on so that tells me that something on the logic board is telling the lamps to come on before the power button has been pressed. Something must be wrong with the logic board, since the OSD is not coming up with the no signal message and the lamps are coming on before the power button has been pressed. Does this sound like a reasonable assumption?

[PlainBill]

Re: CTX S762G - Some Questions...

So I did some further testing. I unplugged the video logic board from the power board and plugged it in. The backlight did not come on so that tells me that something on the logic board is telling the lamps to come on before the power button has been pressed. Something must be wrong with the logic board, since the OSD is not coming up with the no signal message and the lamps are coming on before the power button has been pressed. Does this sound like a reasonable assumption?

Yes. In general when a LCD monitor is first powered up it comes up in the state it was when power was lost. (Pull the plug when the power LED is green and when you plug it in again it will come up with a green power LED. Pull the plug when the power LED is off and the power LED will stay off when it's plugged in again.)

Given that the power led is not responding to the power button, the is no OSD message when it is powered on, and the main chip gets very hot, it's very sick. It could have been killed when you shorted out the transistor, or it could have been when the caps failed.

PlainBill

[EGuevarae]

Re: CTX S762G - Some Questions...

So I did some further testing. I unplugged the video logic board from the power board and plugged it in. The backlight did not come on so that tells me that something on the logic board is telling the lamps to come on before the power button has been pressed. Something must be wrong with the logic board, since the OSD is not coming up with the no signal message and the lamps are coming on before the power button has been pressed. Does this sound like a reasonable assumption?

The reason for the backlight staying off is because the (normally) 5v signal (the BLON,BL_ON, or BackLight ON signal) is sent from the video board to the inverter to turn the lamps on either when the Logic board displays the "give me some input please" or the signal is coming in and the LCD must shine in all it's glory. If the main chip is getting hot it must be shorted and that will explain the always on condition for the lamps (now we know that it is not a short in the inverter section because without the logic board connected the lamps stay off. I can be wrong, but with the provided info, that's what came up to my mind...).

[severach]

Re: CTX S762G - Some Questions...

The gm5120 chip requires a 3.3v and a 2.5v power supply. 3.3v is provided by the power supply board but 2.5v is not so there must be a regulator that produces it which could be burned out. Post pictures if you want help finding it. Test some of the gm5120 voltage pins against the proper values on the data sheet.

[pantherts]

Re: CTX S762G - Some Questions...

Okay thank you very much Plain, eguevarae, and severach for jumping in and giving me some further info. I pulled up the datasheet for the gm5120 and will be doing some more testing tonight on it. I'll also take some pics of the logic board and put them up here. Also, PlainBill, just to clarify because I may not have been clear in my descriptions...the Power LED works as it should. It does turn on and off when pressed but the lamps do not.

[pantherts]

Re: CTX S762G - Some Questions...

And severach, it looks like you are correct. It says in the datasheet that 4 Pins on the GM5120 chip are to be connected to a 2.5v source. That power is for the "Core Power" of the chip. Now, since I measured all of the cables coming off the power board, my guess is something on the logic board is stepping down the power to 2.5v which you mentioned is a voltage regulator.

I must admit something that I did that may or may not shed some light on this issue. Without thinking the other night I plugged the board in and tested the voltages on that P2 cable that goes to the logic board. I then realized only after I had finished that I had forgot that the transistor that I tested in post #22 was not soldered to the board! So I then soldered it in and retook all the voltages. To my surprise the ONLY difference was that they were just slightly lower on the pins that carried current. By slightly I mean like -.10v. Everything else was exactly the same. Upon looking at the datasheet for that transistor I know that it said "Voltage Regulator" at the top of the sheet which originally led me to believe that it could be used as one or something. Does this confuse anyone else as much as it confuses me?

Here's the datasheet thanks to Scenic for linking it: KTC2804

[pantherts]

Re: CTX S762G - Some Questions...

Here's some pictures of the Video Logic board I'm working with:

Logic Board 1
Logic Board 2
Logic Board 3

Notice in Logic Board 3 there is a small SMD starting with the numbers 47 that looks a bit...odd. It looks kinda corroded around it but I'm not sure. Also, for reference the main plug from the Power Board plugs into the white 11-pin plug labeled P608.

P.S.: Sorry for the extremely large size of the photos...I take these at the highest quality I can for detail.

[pantherts]

Re: CTX S762G - Some Questions...

Could someone explain to me how to test one of these with a multimeter? I've already taken it off of the board and I would like to make sure it's not shorted.

AN1431T - Adjustable Output Shunt Regulator

[PlainBill]

Re: CTX S762G - Some Questions...

Could someone explain to me how to test one of these with a multimeter? I've already taken it off of the board and I would like to make sure it's not shorted.

AN1431T - Adjustable Output Shunt Regulator

Measure the resistance between the leads. If it is shorted you will get a very low resistance between two (or all three) of the pins.

This is not a very reliable test. It is better to either test it in circuit or breadboard up the application circuit and test it that way.

PlainBill