HP ZR2740W - Flickered once and then wouldn't turn on

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Transistors can be dead and not look fried.

Possibly you had the board shorting against some metal when you powered it up?

That was my first thought. The transistor that fried is also coincidentally right next to the grounding screw.

However, I did have everything mounted to the chassis as it would be normally assembled so it should have been okay. But there's always the chance of something going wrong when it's being open bench tested like I was.

I will test the transistors on the other board that look good, then. Thanks for the idea.

[Agent24]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Transistors can be dead and not look fried.

Possibly you had the board shorting against some metal when you powered it up?

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Well I cant really say if you understand I would read back through both threads and
on washs thread make notes on how to do the jump - you need to disconnect the wire
to the pson from the main (either de solder it or cut it in a place where you can re -join it
without too much difficulty.) As you say it isnt going to work if you have no 5vstby.
One problem to think about is we have no idea what blew the small transistor on the board
- presumably it could happen again ( any part no marking left on the small transistor?)

Haha I just meant I wanted to make sure that what I was describing, shorting the PS_ON with a resistor, is what you're considering jumping the power supply.

As I suspected without 5V it won't do anything.

Yes, what is odd is that the transistor blew on my GOOD board (Monitor #2) that came from a completely different zr2740w which was working when I took it apart. So, either I somehow messed up when assembling, or my issue with the ORIGINAL (Monitor #1) actually lies in the LCD, TCon, or power switch.

After frying the transistor on the #2 board, I checked the original #1 board thinking maybe I had overlooked this same transistor frying and being the original issue to start with. However, it is fine on board #1 - which is good because I can now read the number printed on it and get a replacement.

[selldoor]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Well I cant really say if you understand I would read back through both threads and
on washs thread make notes on how to do the jump - you need to disconnect the wire
to the pson from the main (either de solder it or cut it in a place where you can re -join it
without too much difficulty.) As you say it isnt going to work if you have no 5vstby.
One problem to think about is we have no idea what blew the small transistor on the board
- presumably it could happen again ( any part no marking left on the small transistor?)

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

The "beige" board in your set is the "power supply" or "power" board In your case the back of it is green. It is a PWB-1421. The black line across the board nominally separates high voltage "Hot" and low voltage "Cold"
Its purpose it to convert a single mains AC voltage into the various low DC voltages 3v 5v 12v and so on required for the main board to function.
In your case it also provides the voltage to drive the led back lights.


The green board is usually called the " main board" but has other names.
e.g "input board" as it has the input sockets. It carries the main processors and its basic purpose is to control and monitor the power supply and to process the signals from the input sockets and on off switch

You also have another small green board shown in washs thread
https://www.badcaps.net/forum/showthread.php?t=42498 that control the picture signals passed from the "main" board to the panel this can be called a Tcon or sometimes a panel board.

As regards PFC it is a circuit included ( in this case) on the power supply board. Budm shows the relevant section in this diagram on washs thread
https://www.badcaps.net/forum/attach...9&d=1418251967 - Most of the components are of course on the top of the board.
Hope that helps a bit

That was extremely helpful. Thank you.

I do recall Budm outlining the power board with the different sections, but I didn't even recall it because I wasn't sure what exactly I was looking at.

Now I can better understand your suggestion to go back to trying to jump start the power supply... And I assume that would be connecting PS_ON with the 5V Standby via a 100-1k Ohm resistor?
I can do that, but on the broken board I do not have any voltage what so ever to the 5V Standby so I don't think that will be jump starting it.

Can you confirm I am understanding correctly?

[selldoor]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Can you help, what is the purpose/name of the green board and the beige board? Which is the PFC?

The "beige" board in your set is the "power supply" or "power" board In your case the back of it is green. It is a PWB-1421. The black line across the board nominally separates high voltage "Hot" and low voltage "Cold"
Its purpose it to convert a single mains AC voltage into the various low DC voltages 3v 5v 12v and so on required for the main board to function.
In your case it also provides the voltage to drive the led back lights.


The green board is usually called the " main board" but has other names.
e.g "input board" as it has the input sockets. It carries the main processors and its basic purpose is to control and monitor the power supply and to process the signals from the input sockets and on off switch

You also have another small green board shown in washs thread
https://www.badcaps.net/forum/showthread.php?t=42498 that control the picture signals passed from the "main" board to the panel this can be called a Tcon or sometimes a panel board.

As regards PFC it is a circuit included ( in this case) on the power supply board. Budm shows the relevant section in this diagram on washs thread
https://www.badcaps.net/forum/attach...9&d=1418251967 - Most of the components are of course on the top of the board.
Hope that helps a bit

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Hi If you still have a set of boards that are supposed to work I think you should go back to trying to jump start the power supply to see if the PFC is working.
You may have been misled or misled yourself here;
AC fuse F801 has .01-.02 Ohm's, if that.

+C802 to -C807 yields 173.5 VDC
C802 yields 85.8 VDC
C807 yields 87.5 VDC

It appears I'm not receiving the voltage I should be at these main filter caps.

No one commented on that but looking back it did need a comment. What you may have missed is that Wash is in Europe so on plug in he had 240VAC which on the big caps would be around 340vDC

As your AC is 120 on plug in vDC IS around 170v


EDIT when/if the PFC kicks in, then the voltage on the caps is lifted to 360vdc-400vdc
whether you are in the US or Europe.

Great info, that makes much more sense.

Can you help, what is the purpose/name of the green board and the beige board? Which is the PFC?

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Did you see the power led lit up? If the power LED lit up and displayed amber color, then the monitor is probably working fine, but it needs to be plugged in to the computer.

One thing I noticed when I tried to troubleshoot power issue on my ZR2740W for not turning on was this:The monitor wouldn't turn on without plugging video cable to the PC, and the power LED was amber.

There are no lights what so ever from the LED next to the button, Amber or Blue.

[selldoor]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Hi If you still have a set of boards that are supposed to work I think you should go back to trying to jump start the power supply to see if the PFC is working.
You may have been misled or misled yourself here;
AC fuse F801 has .01-.02 Ohm's, if that.

+C802 to -C807 yields 173.5 VDC
C802 yields 85.8 VDC
C807 yields 87.5 VDC

It appears I'm not receiving the voltage I should be at these main filter caps.

No one commented on that but looking back it did need a comment. What you may have missed is that Wash is in Europe so on plug in he had 240VAC which on the big caps would be around 340vDC

As your AC is 120 on plug in vDC IS around 170v


EDIT when/if the PFC kicks in, then the voltage on the caps is lifted to 360vdc-400vdc
whether you are in the US or Europe.

[Teeva]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Did you see the power led lit up? If the power LED lit up and displayed amber color, then the monitor is probably working fine, but it needs to be plugged in to the computer.

One thing I noticed when I tried to troubleshoot power issue on my ZR2740W for not turning on was this:The monitor wouldn't turn on without plugging video cable to the PC, and the power LED was amber.

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

I checked this same chip on Monitor #1 thinking maybe this was the original issue, but it was fine.

I wonder if I accidentally did something wrong, or if the LCD panel on Monitor #1 is the issue and this was just the weak point on Monitor #2s pcbs.

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Interesting.

I combined Monitor #2's beige and green PCB, with Monitor #1's LCD panel and power switch and began to get the same results until I smelt burning. Everything was hooked up the exact same to my knowledge, and grounded the exact same.

Here's a picture of what I believe to have burnt, based off location of smoke and appearance after investigating. Unfortunately it's the best picture I can furnish at this time.

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

So I am re-orientating myself with where I left off, and re-performing some tests.

I am giving the name "Monitor #1" to the problematic one, and "Monitor #2" to the previously working one from my office.



With Monitor #1 hooked back up, both the beige and green PCB connected, with the LCD also connected, power switch connected, and even DP cable sending an image:

Voltage over (With power button both idle and pressed):
C802-C807: 171 VDC
P803 PS_ON: 0.00 VDC
P803 +12V: 0.00 VDC
P803 +5V: 0.00 VDC

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

So you do not not PS_ON signal? PS_ON must be present for the PFC Voltage booster to work, you can easily verify that on the working unit.

It does not appear that I have PS_ON signal, as there is 0.0 VDC reading across all pins of P804 and P803, while the working unit does appear to have the correct 5 VDC readings (but no 12v).

I did not follow along with your suggestion to Wash on shorting the PS_ON with a resistor as he actually had some power to this area, and I have none.

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Well that is a laugh - you havent had much time to fix your own machine yet seem to think others have time to help??? Believe it or not we all have lives.
You are lucky in that you have lots of tests in washs thread and have a spare working machine to tests alongside so shouldnt need hands held.

Budm seemed to be working towards finding out if the PFC kicks n when you press the on button, but whilst you seem to have got so far you dont actually
say you did that. So with it all connected and meter on vDC600 connected
+C802 to -C807 what reading do you get when a) plugged in and b)
ON button pressed - you MUST monitor the voltage continuously so may need a helper.

Below I describe my results when checking the voltages across C802 and C807, and although I don't mention it, I get no change when power button is pressed.

I also tested this on my working display, and got the same voltage of ~170 VDC and again no change when button was pressed. This is odd because Wash seemed to get double this.

Thank you, budm

AC fuse F801 has .01-.02 Ohm's, if that.

+C802 to -C807 yields 173.5 VDC
C802 yields 85.8 VDC
C807 yields 87.5 VDC

It appears I'm not receiving the voltage I should be at these main filter caps.

Sorry, the pictures are like that so that the ceiling lights don't reflect and create a glare spot. I'll try and retake them.

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Try putting insulation between the power board and LCD using thin plastic. This will prevent the power board from touching lcd and shorts the circuit.

I found this out after I bought one zr2740w that wouldn't turn on.

I currently am using a ~ 1.5'x2.5' mousepad to insulate between the power boards and metal casing of the LCD. However this is just a temporary setup while I diagnose, are you implying a permanent solution?

[budm]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

So you do not not PS_ON signal? PS_ON must be present for the PFC Voltage booster to work, you can easily verify that on the working unit.

[selldoor]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

I haven't had much time to tinker the past week, but has everyone already given up on me I need help with troubleshooting to isolate the issue in hopes of being able to replace a part

Well that is a laugh - you havent had much time to fix your own machine yet seem to think others have time to help??? Believe it or not we all have lives.
You are lucky in that you have lots of tests in washs thread and have a spare working machine to tests alongside so shouldnt need hands held.

Budm seemed to be working towards finding out if the PFC kicks n when you press the on button, but whilst you seem to have got so far you dont actually
say you did that. So with it all connected and meter on vDC600 connected
+C802 to -C807 what reading do you get when a) plugged in and b)
ON button pressed - you MUST monitor the voltage continuously so may need a helper.

[Teeva]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Try putting insulation between the power board and LCD using thin plastic. This will prevent the power board from touching lcd and shorts the circuit.

I found this out after I bought one zr2740w that wouldn't turn on.

[fl0w3n]

Re: HP ZR2740W - Flickered once and then wouldn't turn on

Well I brought my second zr2740w home from the office so that I could see if I can figure out the issue.

C802 and C807 read the same on the good board, but I do get 5V readings across the 5V pins on the P803 and P804.

With that being said, it seems that my issue is somewhere between the two large black caps and the P804/3

I haven't had much time to tinker the past week, but has everyone already given up on me I need help with troubleshooting to isolate the issue in hopes of being able to replace a part