HP 1955 Monitor Repair Guide

[holoprox]

Re: HP 1955 Monitor Repair Guide

MOSFETS found and changed, ALL OK!

Everything is working fine... for now

[holoprox]

Re: HP 1955 Monitor Repair Guide

1-st post here

48.L1A02.A31 board

changed all capacitors 1000 mF 16->25V
,22 160V (gray ones) with ,22 400~

resoldered most of the board
checked ZD601

is it safe to switch on?

hoq to check Q805 and Q812? between S and D? @200ohm?

[sermulis]

Re: HP 1955 Monitor Repair Guide

Alright. Finally dealt with this monitor. After re soldering bad joints, and fixing cable to logic board, monitor came to life.

[budm]

Re: HP 1955 Monitor Repair Guide

Please post the pictures of the Logic board, both sides, so I can look for the SCH of your board version.

[sermulis]

Re: HP 1955 Monitor Repair Guide

After all came to conclusion that my Power supply board IS OK.
Cut and repaired old sleeve from logic board to control buttons.
Connected all cables back. Now i am not able to see any diode indicator lights on control menu (diodes are OK). Pressing power on button seems doesn't work (silent dead monitor state).

May be someone can provide Logic board chema for this HP 1955 ?

[sermulis]

Re: HP 1955 Monitor Repair Guide

Can you tell me what voltage are you getting at those 4 locations?
Notes: number 4 location are 3 pins, report reading at those 3 pin with the monitor connected to running PC. One of those 3 pin is for BL_ON (Backlights ON), another pin is for Backlights Dimming control, the 3rd pin I do not know what that one is for.

if i understood you right.. than

V1 - 3.3V
V2 - 4.97V (pin to GND)
V3 - 5.07V (pin to GND)
V4 - from left to right - 3.13V, 0.02V, 0.02V (each pin to GND)

[Behemot]

Re: HP 1955 Monitor Repair Guide

Yeah, may be all-in-one regulator, who knows…the thing is, if it works and gives +13something V, it should also give +3,3 to feed the logic board.

[budm]

Re: HP 1955 Monitor Repair Guide

Can you tell me what voltage are you getting at those 4 locations?
Notes: number 4 location are 3 pins, report reading at those 3 pin with the monitor connected to running PC. One of those 3 pin is for BL_ON (Backlights ON), another pin is for Backlights Dimming control, the 3rd pin I do not know what that one is for.

[Behemot]

Re: HP 1955 Monitor Repair Guide

The inverter should be getting 13-13,5 volts, at least that's what inverter in my piece was fed with and worked OK.

Than there is transistor step-down for +3,3 V, probably to directly feed ICs on logic board.

[budm]

Re: HP 1955 Monitor Repair Guide

OK, the power supply is not dead after all since you are getting the 5V, so next step will be hooking up logic board back but leave the flat cable from the logic board that go to the panel and see if those voltage readings change or disappear, especially the 5VDC. one thing does bug me is that you are getting only 13V for the inverter, but then the sch does not match your board 100%.

I will need you to post good closed up pictures of your board, both sides so I can trace out the connections and compare it to the sch.

[sermulis]

Re: HP 1955 Monitor Repair Guide

hmm. maybe i am doing smth absolutely wrong or problem is behind the power board? pinout differs on actual board versus schema. measurements was taken without logic board and lcd panel connected.

[Behemot]

Re: HP 1955 Monitor Repair Guide

If there is NCP1200AP40, those are 40kHz version, hard to get. I just managed to buy 10 pcs so if anybody wants some…

[budm]

Re: HP 1955 Monitor Repair Guide

About 10VDC is correct voltage for NCP1200 SMPS IC to run. Check R615 Source resistor 0.22 Ohm for MOSFET Q601 to see if it is open. Check the DC voltage at the Drain pin of Q601 using C605 Negative leg as the ground ref point for this primary circuit section.
OK, just to sure, you are not getting any DC voltages on these caps?

[sermulis]

Re: HP 1955 Monitor Repair Guide

on D602 i've got 10.9V

Sorry for measleading info. I measured standard diodes not zener ones.

Find proper ones

ZD601 - 10.2 V
ZD602 - 10.6 V

[sermulis]

Re: HP 1955 Monitor Repair Guide

I see.. is it wise idea replacing zener diode without going any further? may be mosfets Q602, Q603 are shortd too, as well as zener diode ZD602.

p.s. sorry for spamming into forum. I am totally new in electric diagrams and repairs greater than simple cap replacing

[budm]

Re: HP 1955 Monitor Repair Guide

Sorry to say, that cannot be, unless the Zener is open. As you can see in the circuit, that 15V Zener is for regulating the VCC for the SMPS IC to be at 15V max.

[sermulis]

Re: HP 1955 Monitor Repair Guide

replaced battery. same results!

[budm]

Re: HP 1955 Monitor Repair Guide

You need to change the battery.

[sermulis]

Re: HP 1955 Monitor Repair Guide

hmm. sometimes multimeter shows low battery indicator. measured one more time. same results. in 20 v range its out of range. will try to find another multimeter meanwhile.

[budm]

Re: HP 1955 Monitor Repair Guide

Right at the two legs? It cannot be that high!, The IC will not take that, your meter's battery is good? It is 15V zener diode.