"dodger741" wrote in message
...

I would start by checking electrolytic capacitors on the lamp ballast,
and
in the power supply for the whole unit. If you reset the bulb timer and
it
still shuts down, then something is wrong with it.

Well I took it apart and found several things. First of all a lot of
tightly packed boards etc - what a nightmare to work on. The ballast
board is very compact with transformers and igniter module, and 2
daughter boards soldered in. I found the current sensing resisters on
the board (10ea 1.0ohm resisters in parallel) and will measure the
current shortly. I found a similiar manual online (EMP 7700) which had
block diagrams and some details about the power supply. They talked
about a 28 pin connector which carries the supply voltages to the main
board. I have a 28 pin connector and all my supply voltages matched
this manual except pin 14 which is listed as 12 volts and I measure 0
(not even a hint of voltage even looking with a scope). There is a
wire in the connector so it is for something. The other item was a
small fan (2.5") which blows on the low voltage board and also the HV
ballast board. The fan doesn't come on. It is a 12 volt fan which is
connected to the LV supply board. The voltage supplied at the
connector is 8 volts with no ripple. I plugged the fan into 12 volts
and it doesn't work. I thought this might be it so I rigged up
another fan to blow on the boards and plugged the unit in. The light
came on but went out in half the time it used to (25min). I am just
turning the unit on (blue screen) with no inputs). Maybe with the
case off etc the air flow is not working correctly which caused this
failure. Seems like I need to disassemble the whole thing to get to
the LV supply board to investigate the 8v fan drive for the 12v fan.
Any more thoughts??

The 8V to the fan may be by design, to run it at a slower quieter speed. If
the fan is bad, fix/replace it first. The circuit may detect the current
draw or RPM of the fan, is it a 3 wire type with a tach signal?