please help me with my Ms. Pac madness..

[vintagegamer]

Taken from the troubleshooting guide, part II, page 20:

"The 7VAC and 7VCT lines are converted to DC voltage by diodes D7 and D8 and filtered by capacitors C7 and C8 to end with +7.5VDC at pin E of the connector. This +7.5VDC is then fed to the collector pin of the D44VM4 pass transistor. A TIP31 transistor may be used as a substitute."

Is it a pretty safe bet to conclude this is the bottleneck that's preventing my board from getting the power it needs to boot, and resulting in the blue screen of death for Ms Pac machines?

And can I get one of these mo-bobs at Radio Shack?

 

[vintagegamer]

power supply diagram:

 

[channelmanic]

Check voltage on both sides of R52. If R52 is bad, you won't have any voltage going to the regulator. The output of the regulator feeds the base of the transistor which keeps the output voltage correct.

Also check R53 to see if it's bad. It's a current pass resistor.

Next check D9.

 

[vintagegamer]

Check voltage on both sides of R52. If R52 is bad, you won't have any voltage going to the regulator. The output of the regulator feeds the base of the transistor which keeps the output voltage correct.

Also check R53 to see if it's bad. It's a current pass resistor.

Next check D9.

OK I can do these tonight. For R52 and R53, do I just set my DMM to ohms and put the leads on each side of those components?

And how do I set the DMM to test D9? Sorry for the retarded questions, I really am trying to become more proficient here.

 

[channelmanic]

Should read high one direction and pretty high to medium high for the other but lower than the other way...

If it reads low both ways then it's either bad or you are reading something else in the circuit and would need to desolder one leg to get an accurate reading.

 

[Riptor]

Here's the little bugger that could be causing me my pain..

Those are obsolete and hard to find. Got a TIP31C?....replace with that.

 

[vintagegamer]

Check voltage on both sides of R52. If R52 is bad, you won't have any voltage going to the regulator. The output of the regulator feeds the base of the transistor which keeps the output voltage correct.

Also check R53 to see if it's bad. It's a current pass resistor.

Next check D9.

with dmm set to ohms, d9 reads .07, r52 reads .05, r53 reads .004

 

[channelmanic]

BUMP!

Replaced the CPU, CPU socket, 1 ROM socket, and the ribbon cable...

Also, there was a short between the regulator transistor and the heatsink. I just swapped the whole transistor/heatsink from another board.

She's running again and will be on the way back to you shortly.