Help me troubleshoot this power supply. FSP043

[JonathanAnon]

Re: Help me troubleshoot this power supply. FSP043

I'm back on this problem again.. I've noticed that the backlight stays on for as long as I hold a resistor between the 12V rail pin and the BL_ON pin...But as soon as I remove the resistor it immediately shuts down...

Would it be safe to join the 12V rail pin to the BL_ON pin with a resistor on a temporary basis, so that I can then check the voltages through the circuit... Or would I risk blowing something? What I'm thinking is that if I can check the pins of the CCFL controller to see if it this chip that is causing the shutdown..

(I've checked the components on the inverter board and I cant find a fault)..

[budm]

Re: Help me troubleshoot this power supply. FSP043

It acts correctly, the BL_ON must be maintained at around 3~5V for the inverter to be on, 0V = off. If you can get the backlight to come on by using the pullup resistor, it means you Inverter board is OK. That means the main board is not sending the BL_ON signal to turn it on.
Since now you have backlights, do you see any pictures on the screen? If not, your main board is really bad.

[JonathanAnon]

Re: Help me troubleshoot this power supply. FSP043

It acts correctly, the BL_ON must be maintained at around 3~5V for the inverter to be on, 0V = off.

OHHHH, this is contrary to another post.... I was under the impression that just an initial >5V signal needed to be sent to the inverter starting transistor to switch on the circuit, but that THEN the voltage to this starting transistor went to zero.... You are saying that the voltage must ALWAYS be present for the circuit to be on....

I know that the VGA board is bad, as it would not work with a known good monitor.... I've noticed that when I attached the VGA board to the power board, the 12V rails go to 14.5V, so I assume there is a short somewhere on the VGA board..

But having confirmed that the inverter is working I will try and source a second hand VGA board..

[jeanbouc]

Re: Help me troubleshoot this power supply. FSP043

Any follow up on this repair....since I am experiencing the same problems with the one I have on my bench repair....thanks!

[JonathanAnon]

Re: Help me troubleshoot this power supply. FSP043

Any follow up on this repair....since I am experiencing the same problems with the one I have on my bench repair....thanks!

Hi Jean, I had two of these that were exactly the same... PSUs with bloated caps, and when I replaced the caps on both (and the voltages came back on line) the monitors still wouldnt work... Seems that the capacitor problems on the PSU led to the main board blowing in both cases.. and I havent been able to source replacement main boards as of yet.

[jeanbouc]

Re: Help me troubleshoot this power supply. FSP043

Hi Jonathan....I went ahead and replace the main board and..."voila"....the monitor is working fine....like a brand new....had also replace couples of buldge caps.....wondering what could have went wrong on the main board (video board)...BYE!.....and thanks for your reply...we will keep in touch...

p.s. I had my 5 and 12 volts from my psu....that is why i started to figure out that the main board was the proble....

[JonathanAnon]

Re: Help me troubleshoot this power supply. FSP043

Hi Jonathan....I went ahead and replace the main board and..."voila"....the monitor is working fine....like a brand new....had also replace couples of buldge caps.....wondering what could have went wrong on the main board (video board)...BYE!.....and thanks for your reply...we will keep in touch...

It's actually very useful for me to know that, Jean.. Helps to reassure me that I was right, and I love being right.. :-)