FAN7547 not operating?

[Behemot]

I got 715G1643-1 board from Fujitsu Siemens P17-2. The owner changed some caps, there was blasted zener diode between +5 and +13,5 V (?). I replaced it and still have no backlight, image is present using lamp.

According to datasheet, if there is no voltage present (this pin is not connected here) on pin 4 (Dimming Mode Selection), it should operate in PWM range, but there is 2,76 V constant voltage without any ripple on pin coming from signal board, making 1,06 V on the Vds pin of the IC itself. I guess I can count that as 1 V 100% brightness?

However, there is definitelly no 200 Hz ripple on OSC pin, see attachement, there are some hundreds of kHz. The same is on COMP (Error Amplifier Output) pin.

I have aprox. 13,6 V on Vcc1 this one is directly connected with the appropriate voltage rail) but nothing on Vcc.

Lamps are not the problem, I have tested different 17'' lamps without any luck. Secondaries of both transformers seem to be OK, all transistors and foil cap in the inverter power section is OK. All ceramics on the output measure OK.

[bammbammfran]

Re: FAN7547 not operating?

I believe that the fan7547 won't turn on without vcc
Did you try tracing back the vcc line

any voltage on the softstart pin 10 ?

[budm]

Re: FAN7547 not operating?

This is the example application circuit, see if the VCC is switched through some kind of transistor.

[Behemot]

Re: FAN7547 not operating?

There is something, will check tomorrow, I have it in my shop. So there indeed should be aprox. 13,6 volts on both Vcc pins, right?

[budm]

Re: FAN7547 not operating?

"So there indeed should be aprox. 13,6 volts on both Vcc pins, right?" Yes. i have a feeling you are missing the drive signal to turn on the switch for the VCC.

[Behemot]

Re: FAN7547 not operating?

There is one more pin coming from signal board which is 0 V, that may be it…

[Behemot]

Re: FAN7547 not operating?

Man screw this, you would not think about that. The owner already opened it for initial recapping, probably bent the pin on signal board connector which was supposed to turn the IC on. I've bent it back, contact is OK and backlight is operating

This is second time, first time there was some Lenovo wide panel which had broken connector for button board. It had no earth so the signal could not go low. I think he has talent for breaking connectors

[bammbammfran]

Re: FAN7547 not operating?

A good clear picture of the bottom of the power supply board might help

[Behemot]

Re: FAN7547 not operating?

No need anymore, the pin which turns on the controller IC is in conductive state once again and it works, see the previous post

[budm]

Re: FAN7547 not operating?

That pin is probably the BL_ON (INVR_ON) pin.

[Behemot]

Re: FAN7547 not operating?

There is no marking on any of the boards but yeah usually something like that…