Re: pin 40 u9 bally mpu -17 no voltage present

Q,

The reset line should just blip LO for a split second at power up, then go
high. Some components involved are VR1, Q1 and Q5. The collector of Q5
should read 4.8VDC. If it is nil, pull U9 and retest. If recovered, bad U9.
If still nil, your Valid Power Detect circuit is somewhat operationally
challenged.

--
-cody
CARGPB4


"qfrost" <qfrost@xxxxxxxxx> wrote in message
news:1180920677.935607.163950@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
HI All-
I've got a Bally 8Ball with a rebuilt mpu that is locked on. Checking
through the usual steps and the guides, I find that pin 40 of u9 never
goes high and has no meaningful voltage.

All the test points on the power supply are good and the mpu tp2
(12vdc) and tp5 (5vdc) are present and correct. The board was one I
bought rebuilt (and supposedly working) and did have work done on the
reset circuit corrosion, so there's that. I suspect something has to
be wrong in the reset circuit despite the repair. Any ideas what to
check specifically? I don't have my schematics unpacked anywhere
right now.

Thanks, Q



.

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