(Topic ID: 317488)

WPC95 failing 5v voltage regulator

By ndz

1 year ago


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  • 45 posts
  • 11 Pinsiders participating
  • Latest reply 1 year ago by Tuukka
  • Topic is favorited by 4 Pinsiders

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#1 1 year ago

WPC95 Scared Stiff wouldn't boot (no 5 volts at driver board or MPU) and was blowing fuse 105.

I assumed a failed bridge rectifier so I replaced the usual suspects.
D7, D8, D9, D10
Capacitor C9.

Still no 5v at driver board. Fuse 105 no longer blows.

I replaced Q1 (LM317k) voltage regulator. Checked all paths and througholes to the best of my ability.

Powered the game up and get one 'bong' then 5 volts goes out on the driver board.

I replaced Q1 voltage regulator again. Powered up with MPU disconnected. 5v is now present. Voltages at MPU connector are correct.

Connected the MPU at J101 and the ribbon cable. Powered up and again one 'bong' and then lost 5v at the driver board again.

Replaced Q1 (third time) and powered up and I have 5 volts again at the driver. I haven't hooked the MPU up again as I expect the same to happen.

What can I check to prevent another Q1 voltage regulator failure before hooking the MPU up again? The connectors and cables test fine. Could there be an issue or short at the MPU causing Q1 to fail on the driver board? Do I need to power up the MPU on the bench or what would be the next step? Thanks!

#3 1 year ago
Quoted from Tuukka:

The regulator should be short-circuit protected, so not burn out very easily. Have you bought the regulators from a reliable source, there are lots of counterfeit LM323's around and maybe also LM317K?
Powering up the MPU on the bench will enable you to measure current consumption, should be about 0.3 - 0.5 amps from the 5V line.

Thanks. The first LM317k replacement was from Marco. Next I bought at 10-pack from Amazon.... But it would be a coincidence if they were bad from both sources. I figured the next step was to either draw 5v from the driver board or put the MPU on the bench. I'll work on it. Any additional suggestions would be appreciated!

#5 1 year ago
Quoted from Tuukka:

Check that your CPU board or connector does not have a short between +5 and +12V, the regulator is usually quite robust but does not tolerate external higher voltages at output.

Yes, I checked the connector and MPU J210 pins and found no shorts. Maybe it's upstream on the MPU.

I'll try to get the MPU on the bench. Thank you!

1 month later
#7 1 year ago

I ruled out the MPU by swapping it with another game. (unless could there be an issue with the game rom or security chip? Seems unlikely)

Same story. MPU starts to boot, I hear one bong, then 5 volts is lost (voltage regulator LM317k on the driver board is toast). This will be the fourth time replacing the voltage regulator to restore 5 volts on the driver board.

Strange problem. It looks like I need to find a way to get the driver board powered up on the bench and draw 5 volts.

#9 1 year ago

Is there an LM317K replacement like the EZSBC? I've been unable to find one.

My regulators were from two sources (marco and an amazon seller). I suppose all could be fakes...

Agreed on the shotgunning. To test the usual suspect components, they had to be removed from the board anyway so I just replaced them first (diodes and cap).

#13 1 year ago

Thanks all for the suggestions. I ordered up a few NTE970's and will report back.

1 week later
#14 1 year ago

She's ALIVE!!!

NTE970 bought from ebay did the trick. Go figure, the LM317K's from marco and amazon were all rubbish.

Thank you all, especially Dumbass for the tip on the NTE970's!!!!

#17 1 year ago

It was a one-off 3 pack from a seller who doesn't appear to have any more. I bought the ones in the NTE bag.

I'll reach out to amz and marco. Thanks again.

#19 1 year ago

Sure. Sorry for the large pic.

BTW, Marco replied immedately, offered refund, and said they have had issues with these before and will alert their procurement dept.

The amazon seller "laptop-part" replied with "could have been damaged in transit" "we have sold lots w/o problem" and referred me to amazon corporate to ask for refund

bad-lm317k (resized).pngbad-lm317k (resized).png
#25 1 year ago

I checked a couple of them and was able to scrape the numbers off with my finger nail somewhat easily. I guess that confirms!

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