CTX S762G - Some Questions...

[severach]

Re: CTX S762G - Some Questions...

ATX power supplies are packed with at least 5 various 1431 and 431 chips. One junk power supply is a lot of spares. The example circuits look pretty easy too.

I don't see any obvious regulators on the video board. Perhaps the power supply is expected to produce 2.5v. No matter since it should be easy to find. With the power off check for continuity between known 2.5v power pins and other parts of the board or the interface connectors.

[pantherts]

Re: CTX S762G - Some Questions...

Excellent information, severach! The yellow and orange cables on connector P2 are not putting out any voltage and I'm not sure if they are supposed to or not. The 2 white cables are also not putting out any voltage. Currently there is nothing whatsoever coming out of them. Here's what I have found out after some research:

There is a 5 Amp Low Dropout Positive Voltage Regulator (PJ1084CZ-3.3) that has it's Adj. (Pin 1) output connected to the yellow and orange pins. I'm currently showing 5v at it's IN (Pin 3), 3.3v at it's OUT (Pin 2), and 0v at its Adj. (Pin 1). I have taken a picture and attached it to this post to clarify the setup and surrounding area of this regulator. I have also shown the voltage readings on the photo of the surrounding areas and the types of components that are there. Anyone see anything wrong in this area?

P2 Blowup 1
P2 Blowup 2
P2 Blowup 3
P2 Blowup 4

[severach]

Re: CTX S762G - Some Questions...

The fixed voltage regulators do not expose an adjust pin. The adjust is fixed internally. Follow the trace around and you'll see that it hits a screw eye which means Pin 1 and those crazy wire colors are definitely ground.

The top two pins go into the backlight PWM so they are probably BLON and DIM. All that's left unexplained is the two white wires.

The circuit surrounding U602 seems quite elaborate and it supplies the two white wires, P6, P7, and P9. It has a heat sink unlike the other chips so it could be a multi output voltage regulator which supplies the 2.5v through the white wires and some other stuff. I was hoping you'd find continuity between the 2.5v pins on the gm5120 and the power interface, possibly on the white wires. You might find different voltages on P6, P7, and P9.

[pantherts]

Re: CTX S762G - Some Questions...

Alright, for starters...I've now identified the orange,yellow,blue and green wires on the P2 connector. They are for the right and left audio channels coming from the logic board's 3.5mm audio jack. I did a continuity test to find this out. Now that leaves us with only the two white wires which also seem to go into the area on the power board that is handling the right and left audio channels (U602). I'm guessing the area around U602 is an audio amplifier circuit.

Second, as for the 2.5v pins coming out of the gm5120 I can't find any continuity between them and the white wires. I have no idea whatsoever what those two white wires are for!

Another thing, not sure if this is supposed to happen or not but I got a nice electric shock when I touched the large heatsink that is beside the power transformer circuit. I measured it and got 70v AC! Could something be amiss in that area? There's a 3 pin transistor fastened to it, labeled Q1 on the bottom of the board. The heatsink is traced on the bottom of the board in white and is the largest "L" shaped one on the board.

[pantherts]

Re: CTX S762G - Some Questions...

Ah ha, okay so I plugged in the logic board and fed power into the setup. I then tested one of the 2.5v pins on the GM5120. Sure enough it is getting 2.5v and I figured out where it's getting it from. On the P2 connector it is getting it from the second to the last pin (or pin10 from the top down) which is one of the white wires! Now the other white wire is only reading about 300mv..shouldn't it be reading the same as the other one?

I'm just very surprised that I couldn't find continuity between the 2.5v pin on the logic board and either of the white wires, but when plugged in sure enough it's getting its voltage at least through one of the wires! I'll work on tracing the other white wire to see if it connects to a 2.5v pin on the GM5120.

[pantherts]

Re: CTX S762G - Some Questions...

I've also tested for continuity between all 2.5v pins off of the GM5120 and the one testing place that I used on the logic board when it was plugged in and was reading 2.5v. So that should mean that each of those pins is receiving 2.5v when powered on.

[pantherts]

Re: CTX S762G - Some Questions...

So now the question is...what is causing the lamps to come on when the logic board is plugged in and what is stopping the OSD from coming up? There's gotta be a short somewhere that is effecting the BL_ON signal right? Should I try to identify where that signal is coming from and trace that through the components? The logic board is multi-layered and is going to be hard to trace but using a continuity test I should be able to make some progress.

[EGuevarae]

Re: CTX S762G - Some Questions...

I have a question.
1.- Do you receive any change in the LCD status (LED) when you apply or remove video signal (Amber with VGA cable not attached, green when attached and good signal, as an example)?
I just want to be sure (let's forget about the stuck BLON signal for now )

[Wizard]

Re: CTX S762G - Some Questions...

GM5120 is grabage. I had one fail in a generic and few brands (like samsung that happen to be unlucky to have one) as well, and performance is so so.

Cheers, Wizard

[pantherts]

Re: CTX S762G - Some Questions...

eguevarae, I tried plugging a VGA cable with a source into the setup and it doesn't effect the LED on the front at all. When I press the button on the front, after the monitor has been plugged in, the LED turns green and stays green regardless if a video source has been plugged in or not. It doesn't seem like it knows the difference whether a video source is being fed into it or not. I have not see the LED turn amber at all.

Wizard,
I was sure hoping this wouldn't be a major thing like the video logic chip burning out but it certainly isn't out of the question.

[EGuevarae]

Re: CTX S762G - Some Questions...

eguevarae, I tried plugging a VGA cable with a source into the setup and it doesn't effect the LED on the front at all. When I press the button on the front, after the monitor has been plugged in, the LED turns green and stays green regardless if a video source has been plugged in or not. It doesn't seem like it knows the difference whether a video source is being fed into it or not. I have not see the LED turn amber at all.

Wizard,
I was sure hoping this wouldn't be a major thing like the video logic chip burning out but it certainly isn't out of the question.

I was hoping to hear a different story. I have two dead monitors with that IC with the same symptoms : green LED, no input detection whatsoever. One is a Pixio 17" and the other is an eMachines 15". I hope you have better luck than me.

[pantherts]

Re: CTX S762G - Some Questions...

Eguevarae, not good. Okay, well I suppose the next step to diagnose it is to literally go pin-by-pin on the gm5120 and verify that it is indeed shorted somewhere inside. That's the only thing I can think of at this point. Tell me, when you plug one of those monitors in, does the gm5120 get extremely hot to the touch within the first 5-10 seconds of being plugged in? If you haven't done that, give it a shot if you have time and let me know. Also, on those monitors of yours, do your backlights come on? How about the OSD or no signal message?

[EGuevarae]

Re: CTX S762G - Some Questions...

Eguevarae, not good. Okay, well I suppose the next step to diagnose it is to literally go pin-by-pin on the gm5120 and verify that it is indeed shorted somewhere inside. That's the only thing I can think of at this point. Tell me, when you plug one of those monitors in, does the gm5120 get extremely hot to the touch within the first 5-10 seconds of being plugged in? If you haven't done that, give it a shot if you have time and let me know. Also, on those monitors of yours, do your backlights come on? How about the OSD or no signal message?

Pixio has a dead inverter section, but the BLON signal is always on, so if the inverter wasn't dead, it would have lamps always on. No OSD, and hot chip. Does not respond to signal input. The eMachines is fried because of the "troubleshooting", and It does not turn on anymore, but I don't remember if the chip gets hot or not.

[Positron]

Re: CTX S762G - Some Questions...

I had to smile reading through all of Pantherts thread. I'm looking down at the same monitor with case apart and the trash can a few feet further. I think I know what to do with mine! Thanks so much for the help!! If it's any consolation... I didn't make it past getting the case of without cracking the plastic at the bottom around the on switch! So kudos to you! On the strange side, My nonstop blinking turned into blink for 3 minutes then stay on. All I did is tighten the ground wire one half turn... Heh , hang in the wall until death maybe!

[EGuevarae]

Re: CTX S762G - Some Questions...

My nonstop blinking turned into blink for 3 minutes then stay on. All I did is tighten the ground wire one half turn...

I've seen that in three monitors from the same model : Planar PL150.
All they had bad was a weak/loose ground connection on the DC input.

[pantherts]

Re: CTX S762G - Some Questions...

Eguevarae, thanks for the information on your monitors. Sounds like the one with the hot chip is exactly what I'm experiencing here. I'm thinking of going to town on that GM5120 and doing tests pin-by-pin comparing it to the datasheet and finding conclusive evidence that the thing is indeed shorted somewhere inside. I know it seems pointless but I just want some closure.

Positron, welcome to the forum! I'm sorry you had to go through a similar experience as me with this trash monitor. The one thing that I hope this thread will do is at least get some information on this monitor out there on the web. Like I stated earlier, doing a search on this monitor only yielded a Russian thread where they said they fixed it by replacing the capacitors. I feel like putting Panasonic caps in this thing was like putting a Ferrari engine in a Geo Metro.

I would give up but I'd like to figure out the WHY of the whole thing. I'd like to be able to conclusively say, ah, it must be the GM5120 that is shorted somewhere inside, or something to that effect.

[PlainBill]

Re: CTX S762G - Some Questions...

Eguevarae, thanks for the information on your monitors. Sounds like the one with the hot chip is exactly what I'm experiencing here. I'm thinking of going to town on that GM5120 and doing tests pin-by-pin comparing it to the datasheet and finding conclusive evidence that the thing is indeed shorted somewhere inside. I know it seems pointless but I just want some closure.

Positron, welcome to the forum! I'm sorry you had to go through a similar experience as me with this trash monitor. The one thing that I hope this thread will do is at least get some information on this monitor out there on the web. Like I stated earlier, doing a search on this monitor only yielded a Russian thread where they said they fixed it by replacing the capacitors. I feel like putting Panasonic caps in this thing was like putting a Ferrari engine in a Geo Metro.

I would give up but I'd like to figure out the WHY of the whole thing. I'd like to be able to conclusively say, ah, it must be the GM5120 that is shorted somewhere inside, or something to that effect.

One easy way to do that would be to replace the chip. It's only got 208 pins. OK, it might not be that easy.

PlainBill

[pantherts]

Re: CTX S762G - Some Questions...

Plain, no I don't think I would be going that far. If testing the chip doesn't pan out I guess I'll just be gutting the thing for parts. Is the LCD even worth keeping? I don't know enough about LCDs to know whether LCDs are interchangeable with other monitors that use a similar setup. Anyone know?

[EGuevarae]

Re: CTX S762G - Some Questions...

Plain, no I don't think I would be going that far. If testing the chip doesn't pan out I guess I'll just be gutting the thing for parts. Is the LCD even worth keeping? I don't know enough about LCDs to know whether LCDs are interchangeable with other monitors that use a similar setup. Anyone know?

They are. I've seen Samsung & dell monitors that use the same Samsung LCD panel. I've used panels from Proview monitors on other brands and then I've changed HP 1703 panels into other units. Several LCD Monitors use the same panel, so keep it safe. It may come in handy later. Even the lamps to test inverters can be used later. Just don't trash the panel. And the PSU can be used too, for parts or on other units.

[pantherts]

Re: CTX S762G - Some Questions...

Eguevarae, you've saved many a part from the local landfill. Consider yourself a savior of electronics at this point. Thank you for all your help with this monitor. I have gained utmost respect for this form and the electronic know how of this forum. I'm planning on remaining an active member and want it to be known that anyone can contact me on AIM for testing purposes or information purposes if they need. Thank you to everyone for participating in this thread. YOU ROCK BADCAPS.NET!