(Topic ID: 260312)

Need Help Diagnosing Power Supply


By Crash

6 months ago



Topic Stats

  • 6 posts
  • 3 Pinsiders participating
  • Latest reply 6 months ago by Crash
  • No one calls this topic a favorite

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Topic poll

“What should I look at next?”

  • Replacing the regulator IC 0 votes
  • Replacing the bridge rectifier 0 votes
  • Checking surrounding 5v circuit resistors and diodes 0 votes
  • It's fine 0 votes

(Multiple choice - 0 votes)

This poll has been closed.

#1 6 months ago

The power supply in my Police Force is putting out a weak 5v supply. Before it was putting out 4.95v and causing the game not to boot. The key thing is I removed all connectors from the board except the AC input connector and it was still showing only 4.95v at the test point. The caps were original so I replaced all of those. This brought the 5v up to 4.96v and the game boots reliably now. I also verified there are no bad solder joints and damage to the board. However, I'm trying to bring it up to at least 5.00v (for headroom). The 2N6057 power transistor was so old the markings had vaporized. After replacing this I saw no change.

I then looked at the MC1723CP regulator IC and pins 4 and 5 are showing 4.96v. This shows the circuit is balanced. I also verified the 9.8vAC coming to the board. What else could I check? Should I still replace the original 30 year old regulator IC? Or maybe replace the bridge rectifier in the event the voltage from it is slightly low?

I also considered the possibility there is a resistor that is off somewhere else is the circuit causing the MC1723CP to become miscalibrated against the 5.00v output it should be. I just want to bulletproof this board now before it goes out on location where it will run 24/7 365 at a laundromat.

#2 6 months ago

You are just dealing with the tolerances in the parts. Some will be above and some will be below. If a couple of the parts are both below tolerance then you get a slightly low output, but is still within spec's.

#3 6 months ago

You're probably right, the old caps were likely the only issue in terms of current carrying capacity.

#4 6 months ago

If you are certain that there is no issues with the power supply other than a slightly low voltage output then you can raise the output .05 volts by replacing R-8 with the next larger resistor (5.13K Ohm). This would give you a 5.01 volt output.

#5 6 months ago

I wouldn't think 4.96vdc would give you problems on a system 11, they're more tolerant than wpc. Have you replaced the male headers and replaced the idc connectors with molex on the power supply? How about the power connector on the mpu? Inconsistent booting can also be a bad c30 on the mpu (next to the batteries), has that been changed?

#6 6 months ago
Quoted from gutz:

I wouldn't think 4.96vdc would give you problems on a system 11, they're more tolerant than wpc. Have you replaced the male headers and replaced the idc connectors with molex on the power supply? How about the power connector on the mpu? Inconsistent booting can also be a bad c30 on the mpu (next to the batteries), has that been changed?

That would make sense as I've noticed WPC games seem to have more trouble with resets. Actually the 5v supply on my Elvira is so bad the LED displays are getting dim. Yet the game actually plays fine. I'll give Police Force some play and check the rest of the chain if I'm still having issues.

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