Hp 2035 monitor Check the Signal Cable

[mikey5791]

I will agree with Steve on checking the ESR of the capacitors in the power supply. Recently I had come across my Acer monitor model AL1717 which suddenly just show black screen on and off intermittent even though I have been using it daily for the past 5 years.
The bad capacitors does not even show signs of bulging or leaking electrolyte but unsoldering it off circuit and test ESR by comparing it to a new cap will detect those bad ones.

 

[pharaon]

I would be checking the ESR of the capacitors in the power supply. I've taken a look at your photos and none of the capacitors look stereotypically faulty.

i already changed two bad capacitors in the power supply board but the problem still exist

 

[pharaon]

anything else i should try?

 

[(*steve*)]

Show me which capacitors you have changed.

 

[pharaon]

Show me which capacitors you have changed.

the other two caps were fine

 

[(*steve*)]

I probably would have changed the two on the right hand side if I was already changing the others.

And I agree with screwing that device to the heatsink. I assume there's nothing connected to the other side of that heatsink?

Have you measured the output voltages on the power supply? I would do so on both the DC and the AC range of your multimeter. Depending on your meter, you should read almost 0V on the AC range.

 

[pharaon]

I assume there's nothing connected to the other side of that heatsink?

no there's nothing.

Have you measured the output voltages on the power supply? I would do so on both the DC and the AC range of your multimeter. Depending on your meter, you should read almost 0V on the AC range.

where should i measure it? at the wires going to the monitor " input circuit" and what voltage should i be expecting

 

[Bluejets]

Looks like that varistor over on the right hand side has either been physically damaged or errupted under some fault.(3101)
Sure looks old......
Switcher IC can sometimes go open but it doesn't seem to have had much heat around it.
Wonder why the screw was missing..?? maybe the mosfet has popped, did you test it at all..?
A few caps in that area that could have gone belly-up.
Did you test any of those..?

 

[(*steve*)]

where should i measure it?

The ribbon cable leading away from the right side of the board contains the various voltage rails.

You're likely to find that one side of all the capacitors you changed ( and the other two I pointed out) have one side common. That will be your ground rail (measure voltages with respect to that).

The other side of most of the capacitors will be directly connected to the other pins on ribbon cable.

You should be expecting voltages like 3.3V, 5V, 12V. Tell us what you read and we can give you an idea if they sound right.

 

[pharaon]

Those are the measurements, the left one is negative and the one with black dash is negative

 

[(*steve*)]

I'm not sure which ones are negative (or do you mean that the three with the black pen markings are all connected to ground?). Can I assume that you made these measurements with the main circuit disconnected from the power supply?

It looks like a regulated 3.3v output with the other floating a little high due to the lack of a load.

The three reading 0V appear to be very low current connections (note the narrow traces) so these may be signal inputs (or outputs) to the power supply, possibly to indicate when to turn the back light on, or to indicate a power good status.

Can you measure these tails on your AC range? Also preferably with the load connected.

 

[pharaon]

Can I assume that you made these measurements with the main circuit disconnected from the power supply?

this is the power supply main circuit, the other circuit board is the input board.

Can you measure these tails on your AC range? Also preferably with the load connected.

will do so

 

[(*steve*)]

What I mean is, were the two boards disconnected from each other when you made the measurements?

 

[pharaon]

What I mean is, were the two boards disconnected from each other when you made the measurements?

Yes it was disconnected from each other

 

[(*steve*)]

Please repeat the measurements with the boards connected. Please remember to take measurements on the AC range as well as DC.