HP 1955 Monitor Repair Guide

[retiredcaps]

Re: HP 1955 Monitor Repair Guide

The logic board is the board with the the connectors on it? (DVI, VGA, USB etc.?)

Correct.

In addition, can you just restate what the latest activity of the power LED and screen is? With the number of components being removed and tested, I just want to see what the current state is. Please also connect a working computer to the LCD to view your desktop.

[krantz]

Re: HP 1955 Monitor Repair Guide

Restatement: I have a 1955 that I am trying to get working. I have changed all the caps except for the 150uF 450v. I cant see any blown FET's or anything else that might be shorted. What could it be?

Plus I found out that there are two more caps on the power board where the C5707's are and two more at the power-connector. The grayish ones.

I have desoldered the inverter fuse 5A 125V, measured it and it has very low resistance (0.4 ohms).

I have measured the 4431 FET's, the signaling transistors (no shorts, like you know), the four transformers near the C5707 transistors, the diods on the top surface with resistance and diod settings on the multimeter.

[retiredcaps]

Re: HP 1955 Monitor Repair Guide

In addition, can you just restate what the latest activity of the power LED and screen is? Please also connect a working computer to the LCD to view your desktop.

And what about the above? What are the current symptoms?

[krantz]

Re: HP 1955 Monitor Repair Guide

Ah, sorry.

I get a picture from the computer with working backlights for about a second, then the screen restarts in an continous loop. Also the power-on-board on the front of the LCD restarts with the green LED lighting on and off at the restarts.

[alexanna]

Re: HP 1955 Monitor Repair Guide

Ah, sorry.

I get a picture from the computer with working backlights for about a second, then the screen restarts in an continous loop. Also the power-on-board on the front of the LCD restarts with the green LED lighting on and off at the restarts.

If I am understanding things correctly, When you removed the fuse for the inverter you were able to get normal operation of the front power switch [you could turn it on and off], and you can see a power light that indicates you are receiving a signal?
You have used your ohmmeter on the 200 ohm scale,[The 200 ohm scale is important] and you are not seeing a very low ohm reading between any of the pins on the transistors or FETs?

[krantz]

Re: HP 1955 Monitor Repair Guide

If I am understanding things correctly, When you removed the fuse for the inverter you were able to get normal operation of the front power switch [you could turn it on and off], and you can see a power light that indicates you are receiving a signal?
You have used your ohmmeter on the 200 ohm scale,[The 200 ohm scale is important] and you are not seeing a very low ohm reading between any of the pins on the transistors or FETs?

That is correct. But when I removed the fuse I didnt get a picture or the backlight didnt power on. (?)

[alexanna]

Re: HP 1955 Monitor Repair Guide

It appears the power supply is shutting down under a load, reinstall the inverter fuse, and try replacing any start up caps. These are usually around 50v and below 47uf

[krantz]

Re: HP 1955 Monitor Repair Guide

You mean the two grayish rectangular components at the power connector and the two at the transistors?

Refer to attachment pictures.

[alexanna]

Re: HP 1955 Monitor Repair Guide

No the small aluminum caps just above the gray one in the first photo.

[krantz]

Re: HP 1955 Monitor Repair Guide

No the small aluminum caps just above the gray one in the first photo.

The caps (two battery shaped) at the ic?

Or the two blue ones at the power-connector?

Updated: Electrolytic capacitors, yeah. Like I said. I changed them all.
I guess I need to wait for my new multimeter (Fluke 179) so that I can check the capacitors with that. Maybe they're defective?

[PlainBill]

Re: HP 1955 Monitor Repair Guide

The caps (two battery shaped) at the ic?

Or the two blue ones at the power-connector?

The two circled in red. One of those is the start-up cap. If it fails completely you will not have any power at all. If it is marginal (capacitance is seriously reduced) the power supply will start and appear to work normally, but will fail under full load - such as when the inverter starts.

PlainBill

[jetadm123]

Re: HP 1955 Monitor Repair Guide

The caps (two battery shaped) at the ic?

Or the two blue ones at the power-connector?

Updated: Electrolytic capacitors, yeah. Like I said. I changed them all.
I guess I need to wait for my new multimeter (Fluke 179) so that I can check the capacitors with that. Maybe they're defective?

I think folks may have missed it when you initially said that you had already changed all the caps (post #56) except for the large 450V one. Perhaps the question that should be asked is: what brand/series caps did you replace the original caps with?

[krantz]

Re: HP 1955 Monitor Repair Guide

All the caps i replaced to are Rubycon.

[alexanna]

Re: HP 1955 Monitor Repair Guide

The startup cap is critical to have the correct series.
You look to have somewhat of a difficult monitor to repair.
Do you have a good CCFL that is not installed in a monitor panel?

[krantz]

Re: HP 1955 Monitor Repair Guide

No, I dont.

I have a lcd monitor that has a CCFL in it but can I get it out to test the board with it?

[jetadm123]

Re: HP 1955 Monitor Repair Guide

All the caps i replaced to are Rubycon.

What series are the Rubycon's? It will be a 2-3 letter designator stamped on the cap. Something like: YXG, ZL, ZLH, etc.

[alexanna]

Re: HP 1955 Monitor Repair Guide

I have had transistors that did not show a short,cause the power supply to shut down.
Without removing the test CCFL from your other monitor.
Unplug all of the CCFLs from the 19" you are working on.
Plug in your test ccfl into one connector on the inverter on the 19", power the monitor on.
Dose the back light and PLED still flash?
Repeat this with the other 3 CCFL connectors,Dose anything appear different?

[krantz]

Re: HP 1955 Monitor Repair Guide

I have had transistors that did not show a short,cause the power supply to shut down.
Without removing the test CCFL from your other monitor.
Unplug all of the CCFLs from the 19" you are working on.
Plug in your test ccfl into one connector on the inverter on the 19", power the monitor on.
Dose the back light and PLED still flash?
Repeat this with the other 3 CCFL connectors,Dose anything appear different?

I tried it. At first I used just one connector from the CCFL and it worked. Tried two, worked. Tried three, worked. Tried four, it started flashing on and off but the power switch LED did not flash (restart). Tried it again and now the test-CCFL's stay on and the power switch isnt restarting.

Tried it again after having the power cord unplugged - the CCFL's and power-switch LED is restarting again. Caps anyway?

[alexanna]

Re: HP 1955 Monitor Repair Guide

What were tge series of the start up caps?
Did you re-solder the gray box type caps by the 5707 transistors

[krantz]

Re: HP 1955 Monitor Repair Guide

You mean what uF and V-capacaty?

I never desoldered the gray box type caps but the 5707's. Only the one in the picture to know what it was.