Gateway FPD1965, no power

[jsog]

This Gateway FPD1965 is totally dead, no power light, doesn't twitch when the power button is pressed. All fuses are good, or at least the ones I found. The power resistor R904 measures 0.7 ohms. There is power coming in, 173VDC at the big capacitor.

That 173VDC is fed to pin 3 of the LD7552B PWM controller (IC901) through 3 series resistors (R909, R910, R931). It drops to 112 after the first resistor, 56 after the second, and is only 0.2V at pin 3 of the chip.

The Q903 FET has a resistance of no less than 9.5K between all pins.

Voltages on the digital board connector are all zero. Interestingly, whoever designed this chose to use the exact same connector type for power and keyboard input on the digital board. (No, I didn't attach them the wrong way, although maybe whoever had it before did.)

All electrolytics replaced with Panasonic FR and FC. None of the originals were visibly bad, or had bad ESR.

Should I replace the LD7552B? What US sources are there for replacements?

[PlainBill]

Re: Gateway FPD1965, no power

This Gateway FPD1965 is totally dead, no power light, doesn't twitch when the power button is pressed. All fuses are good, or at least the ones I found. The power resistor R904 measures 0.7 ohms. There is power coming in, 173VDC at the big capacitor.

That 173VDC is fed to pin 3 of the LD7552B PWM controller (IC901) through 3 series resistors (R909, R910, R931). It drops to 112 after the first resistor, 56 after the second, and is only 0.2V at pin 3 of the chip.

The Q903 FET has a resistance of no less than 9.5K between all pins.

Voltages on the digital board connector are all zero. Interestingly, whoever designed this chose to use the exact same connector type for power and keyboard input on the digital board. (No, I didn't attach them the wrong way, although maybe whoever had it before did.)

All electrolytics replaced with Panasonic FR and FC. None of the originals were visibly bad, or had bad ESR.

Should I replace the LD7552B? What US sources are there for replacements?

Great pictures, great detail in your description, great job of troubleshooting. This is so far from the 'my monitor dont work what do i replace to fix it" posts I was motivated to go a few extra steps. Unfortunately I can't help much.

The symptoms point to a defective LD7552B. I have not found a US distributor of the part, however several sellers on eBay have them available as a LD7552BS (the SMD version). Most are based in China. The best is a gentleman with 99.9% positive feedback who will sell 10 for a total of $12, including shipping.

PlainBill

[jetadm123]

Re: Gateway FPD1965, no power

Pins 3 and 7 are the VCC for LD7552. MAX VCC for this chip is 36V. Try measuring VCC again using pin 1 on the LD7552 as your ground.

[jsog]

Re: Gateway FPD1965, no power

PlainBill: aw shucks, thanks. Just trying to anticipate what would might be useful. You've helped me before, too.

jetadm123: That 0.2V was between VCC (pin 3) and GND (pin 1) on the chip. It's a good point, the chip ground is totally isolated from frame ground.

[jetadm123]

Re: Gateway FPD1965, no power

I suggest you also measure the voltage at pin 7, since they're probably not using both Vcc pins.

[jsog]

Re: Gateway FPD1965, no power

Fair enough, remeasured today. Pins 3 and 7 are connected, now at 0.29V.

[PlainBill]

Re: Gateway FPD1965, no power

Fair enough, remeasured today. Pins 3 and 7 are connected, now at 0.29V.

That confirms it - the SMPS controller is dead.

PlainBill