Merit Force

[Larry]

Motherboard is shutting down the power supply. I have changed all 1000uF and 470uF elec caps. I have changed the 3004 power contoller chip and the two MOSFETS. No change. Any ideas?

[lilshawn]

monitor or the computer???
(being the monitor section)

which setup is this? which motherboard?

i would have first changed the power supply.

[Larry]

Motherboard.  It's gold and green. P61WP-FE.  I already changed the power supply, it  was bad.  Swapped the processor too.

[lilshawn]

if it boots up, runs for about 1-1.5 seconds then shuts off, try resetting the BIOS. often if they overheat they will loop like that.

remove the battery and look for a jumper to reset the bios. not sure exactly where it is.

failing that try to manually jump the power supply to get it running. pull the power plug and Jump the green (should be green) poweron wire to the black wire next to it. this will cause the power supply to remain on. hit the power and see if the board boots. if it does leave it on until the board begins to boot. then shut it off and see it will start up normally.

sometimes a bad memory stick will cause the board to not boot properly too as well.

[Larry]

Thanks for trying to help.  I have 2 boards.  One works, one doesn't.  The PS is shutting down immediately.  Not even a twinge on the CPU fan.  I have swapped the BIOS, CPU and memory stick from the bad board to the good board and it still boots.  So it can't be any of those.  Grounding the power on doesn't help either.  Any other ideas?  Do you knoe what the green LED indicates?  It stays off on the bad board.

[lilshawn]

the led should show the status of the VSB+5v, it's the 5 volt standby voltage. ATX motherboards don't actually turn off, hence the voltage it uses to turn itself on and to keep memory stuff alive during standby.. if it's staying off i'd try measuring the vsb line with a voltmeter at the connector to see what it is. should be a purple wire. if it's low, you may still have a bad cap someplace on the vsb line (check the caps around the memory and the pci slots. if it's dead, make sure it's actually outputting. they only output a small number of amps (sometimes under 1) and are easily overloaded. (unplug the power and the motherboard header and let the supply settle. then power up the supply and measure the vsb (should be 5v) if so, while still measuring, plug it in and see if it dips (around 2 volts) then shuts off. if so, you might have a bad power mosfet or another shorted cap someplace.

[Larry]

It turned out to be the PS and the processor.

[Rickn]

When you get it fixed and if it is a Tatung Monitor, be sure to check the value of R991 on the neckboard. They originally used a 3.3ohm resistor and this caused the heater voltage to be way to high. it should be a 6.8 ohm resistor or your tube will lose all it's colors one by one.

Good luck Rick N