hp 1940. injecting 12/5V from the pc psu.

[senndogg]

it is a bad idea. but how bad is this?

i failed several times in repairing the primary circuit of a lightning-strucked HP 1940 monitor. i decided i should replace the whole PSU but the customer did not want to put that money on the old monitor. so i followed plan B.

will it work?

[senndogg]

Re: hp 1940. injecting 12/5V from the pc psu.

oops. sorry for the first pic.

[senndogg]

Re: hp 1940. injecting 12/5V from the pc psu.

it was a Delta 350W genuine psu.
voltage with the monitor disconnected 11,823V
it was an old Pentium 4 s478 with onboard video.

[retiredcaps]

Re: hp 1940. injecting 12/5V from the pc psu.

it is a bad idea. but how bad is this?

One retiredcaps point for showing a picture of your multimeter.

I thought about doing the same modification for a Sony 17 inch LCD that I picked up for free. It is missing the AC adapter and I don't want to buy a new one for a monitor that I don't know if it works or not.

So I thought about using an ATX power supply to apply power to the lcd. I haven't done it yet since I have other projects ahead of it.

[amazinguk]

Re: hp 1940. injecting 12/5V from the pc psu.

if you change the Bridge Rectifier and the next 2 resistors in high voltage area, (in second picture) maybe u gona have fix the best idea, MAYBE never done that before, wish you luck.

[senndogg]

Re: hp 1940. injecting 12/5V from the pc psu.

@retiredcaps: if i get good feedback for the next 3 months, i'll consider this test passed and i'll apply it more often wherever the customer will not afford a new psu.
@amazinguk: thank you mate, but i replaced for 2 or more times: the rectifier, the low-ohms resistors near the fet, the fet, all the diodes, the startup caps etc, and in all cases i got a tremendous explosion near the fet area. as i understood later, the IC was faulty and instead a sinewave it brought dc voltage in the fet gate.

[Scenic]

Re: hp 1940. injecting 12/5V from the pc psu.

I've done something similar a couple times before.
Once on a Belinea 19" 1280x1024 LCD, which had a messed up PSU and once on a noname (Yuraku !?) 19" widescreen 1440x900 LCD with a completely FUBAR'd PSU.
Primary side on the Yuraku was completely blown to pieces and I couldn't read any part numbers. To make matters worse, the PCB had absolutely no model markings to search for..

The Belinea just needed 12V, the Yuraku needed 12V (inverter) and 5V (logicboard)

For the Belinea, I just put a regular DC barrel socket in the monitor case and removed the 230V socket, and for the Yuraku I hardwired a computer power cord into the monitor (ground, 5V and 12V), and the other end just has a regular 5.25" molex socket (like you'd find on a HDD or computer fan) so I can plug it directly into the computers PSU.

If current draw on 5V isn't too high, you might get away with using a 7805 linear voltage regulator for 5V, so all you need as a power input would be 12V (for the inverter and feeding the 7805 for the logic board)

PS: I'd never use the standard power socket on a modification like this. That's just an accident waiting to happen (someone plugging 230V straight into these now 5V/12V inputs..)

[senndogg]

Re: hp 1940. injecting 12/5V from the pc psu.

PS: I'd never use the standard power socket on a modification like this. That's just an accident waiting to happen (someone plugging 230V straight into these now 5V/12V inputs..)

i wanted it to look as factory as possible. people get scared with the extra wiring hassle and stuff. anyway the old couple (who use this pc just to get in contact with skype) will never adventure playing with the cables in any other case i am not using this socket again.
ps.: thank you for the 5V regulator idea.