Monitor HP1502 - Power supply board 715L1034-1 Failure - NO POWER

[Axxel]

Hi everbybody!

I Have a VGA monitor HP1502 and the failure is NO POWER. No led, no Power, nothing. The power board is a 715L1034-1

So I tried to find some diagrams o Service manuals and I found those PDFs :

In the HP L1502 Service Manual.pdf attached document, I can see the power board doesn't match with the 715L1034-1. Very interesting for fixing the scaling board but in my case it's useless...

In the 715L1034-1 Diagram.pdf attached document, there is the complete diagram of the 715L1034-1 power suppply board, exactly at page #34-35.

So I started to make the following basic changes on the board:

Replaced Q903 - K2996 Mosfet Transistor
Replaced IC901 - SG6841 PWM Controller
Replaced IC902 - PC123 OptoCupler
Replaced Q901 - A733 PNP Transistor
Replaced Q902 - K945 NPN Transistor

Following with no power result

I'm living in Mexico so I have 120VAC @ 60 Hz.

All the results of these meditions are maked with the board disconected of the scaling board (This one do the gestion of the POWER switch)

The rectifier of the primary of the power supply board seems to be OK. At the output of the diode bridge I have 170VDC.

Now I'm checking around the PWM Controller SG6841. (PDF Attached).

Pin 1 - GND - Looks to be OK
Pin 2 - FeedBack - 0V (Nothing) - At oscilloscope 0V (Nothing)
Pin 3 - Vin - 0,75VDC
Pin 4 - Reference Settings - 0V (Nothing) - At oscilloscope 0V (Nothing)
Pin 5 - Temperature Protection - 0V (Nothing) - At oscilloscope 0V (Nothing)
Pin 6 - Current Sense - 0V (Nothing) - At oscilloscope 0V (Nothing)
Pin 7 - Power supply - 0.04VDC (The problen shoud be there? The IC is unpowered?)
Pin 8 - Drive Output - 0V (Nothing) - At oscilloscope 0V (Nothing) - I shoud have a square signal here I think...

Now I will check the outputs of the 715L1034-1 power supply board:

Pin 4 Shoud give 5V permanent - And I have 0V - Nothing

Where I can look to fix this board?

Regads, Axel.

[stj]

Re: Monitor HP1502 - Power supply board 715L1034-1 Failure - NO POWER

replace c907, check resistors r904-907

[Axxel]

Re: Monitor HP1502 - Power supply board 715L1034-1 Failure - NO POWER

Thanks for your answer.

The values of the resistors on the board are different as the values I have on the diagram.

R906 & R907 are marked 684 - So 680K? I tested with the multimeter and I measured the correct values (680K).
R905 & R904 are marked 105 - So 1Mohm? I Quited them and the multimter gives me 1Mohm for each one... So seems to be good

Those resistors R906 & R907 are marked 1Mohm on the diagram... They are 680Kohms on my board

I replaced C907 for a 10uf 50V Cap. Originally on my board C907 was 22uf 50V.

I don't noticed any change...

[kaboom]

Re: Monitor HP1502 - Power supply board 715L1034-1 Failure - NO POWER

Use what you had on your board. 22u/50v for C507. Check D902, D904, ZD901 for shorts- if suspect, replace.

[Axxel]

Re: Monitor HP1502 - Power supply board 715L1034-1 Failure - NO POWER

Hi.

Thanks for your answer.

I replaced C907 for a 22uf 50V.

D904 D905 D906 ZD905 CN902 are absent on my board. This part of the circuit don't exist.

I ckecked ZD901, multimeter in diode mode, 0.73V for one side, nothing for the other, so I think ZD901 is OK.

When I power the board, I have 1V at the pins of ZD901 and this tension goes down slowly slowly 0.9V ... 0.8V.... 0.7V...

IC901 is mounted on a base so I can quit it o replace it easily. When I quit it, I have a tension of 148V on pin 3 instead of 0.75V.

[momaka]

Re: Monitor HP1502 - Power supply board 715L1034-1 Failure - NO POWER

I don't know if it's the pictures or not, but what I see are several bulged capacitors on the output.

[Axxel]

Re: Monitor HP1502 - Power supply board 715L1034-1 Failure - NO POWER

This is the fault of the pictures, I changed all the capacitors.

[momaka]

Re: Monitor HP1502 - Power supply board 715L1034-1 Failure - NO POWER

I think the problem is that you have almost zero voltage on pin 3 of the SG6841 PWM controller. If you look under "Under-voltage Lockout Section" on page 5 of the SG6841 datasheet, it says that typical threshold voltage is 16V and minimum operating Vdd voltage is 10V. That said, you won't get a voltage on Vdd until there is at least 16V on pin 2 (Vin) -AND- if the primary auxiliary rail that feeds Vdd is good.

So you need to check why pin 2 (Vin) on the PWM controller is not getting any voltage.

If you have an 12-15VDC non-grounded, unregulated power adapter -OR- 20V regulated but non-grounded, you can use that to feed pin 2 (Vin) the necessary voltage to see if the controller will start. However, you will have to be really careful with this because the return/common pin of your power adapter needs to connect to the live-side common. If everything is right with the rest of the circuit, the monitor should power up.

[Ayo.Workshop]

Re: Monitor HP1502 - Power supply board 715L1034-1 Failure - NO POWER

hi have this same mainboard, the only thing is that the ic sg6841d explode at the moment that i plug in the current