(Topic ID: 68023)

TECH: WPC-89 MPU Won't Boot - Bet You Have Never Heard Of This One!


By robgo777

5 years ago



Topic Stats

  • 13 posts
  • 5 Pinsiders participating
  • Latest reply 5 years ago by robgo777
  • Topic is favorited by 2 Pinsiders

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#1 5 years ago

So, one bazillion dollars to whoever figures out the cause...

There I was... Eating, Drinking, and being Merry while playing my TZ. Suddenly, out of nowhere, the machine gives me a switch error then dies. So after coughing up the Cheetos I started to choke on, I tried restarting the machine. No Joy... all I get are the LEDs D19 and D21, no blinking D20. When the machine it turned on, only those two LEDs are solid, no blinks or anything from D20. The nerve of some machines!

Tested all voltages, what I have found is that the board is getting the proper voltages with the exception of U21 pin 3. There is no 5vdc coming from that pin on that chip. I am however getting 5vdc going to the banded end of the diode at D25, however the non-banded end is not registering any voltage. Easy fix right? Just replace the diode you say? Well I did and no change! In fact, what I have found is that when the non-banded end of the diode is removed from the board, it registers 5vdc however as soon as I touch it to the board, bahhm! Voltage drops! When I remove C50 and R90 the diode at D25 will keep it's voltage after attaching back to the board. However as soon as I put C50 or R90 back in, the voltage drops again.

I did remove the board from the game BTW and am in the process of bench testing it with a switching power supply.

Replaced the following chips with working ones from my IJ:

U4
U6
U9

Replaced the following chips and components with brand new ones:

U1
U2
U3
U5
U7
U8
U10
U12
D25
C50

Still no joy. Tested voltage at U10 pin 1 and am getting 4.85vdc.

Any guesses?

#2 5 years ago

Well I don't want to send you down the wrong path but it sounds like you may have dove in too deep, this sounds like the classic WPC reset...4.85 may too low for your watch dog circuit. Are the driver board LEDs all showing that you have all the required voltage (5V, 12V, 18V etc..) If not go back and check the BR and Cap, not 100% sure but BR2 and C5 and start there...if you get anything around 8VDC at the BR, you're good. Then move to C5 now this one is critical you must get 5VDC or very close to out of the leg of that cap. If good then move to the Voltage Reg, you should get 4.9 or near that out of the output leg. Do these things first.

#3 5 years ago

Thanks kvan, but isolated the power supply already. It is a problem with the MPU. This MPU has been connected to 3 different power boards from 3 other working games, plus the bench power supply and still have the same issue. Watchdog resets below 4.7vdc at U10.

I would however be interested in finding out how to disable the watchdog feature just to rule that out. I see there is a section of the MPU for watchdog disable, but I have never had to do that before.

Rob

#4 5 years ago

I just fixed an MPU with a similar issue. One of the gates of U21 (pin 3) was affecting the reset signal. The board would sometimes boot, sometimes not. It definitely would not boot with J202 connected.

I see that U21 is not on your list...give it a go! It's a 4584.

It's helpful, with odd issues like this, to have the failed board side by side with a working board on the bench. Systematically probing around with a DMM in diode test finds a lot of problems.

Let us know what you find.

Oh ya...One Bazillion will be nice. First thing I'll do is eliminate the national debt...then I'll use my largess to prevent congress from wasting any more of our money. Would that work for you?
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

#5 5 years ago

Replaced U21, still same issue.

Thanks for the try Chris!

Rob

#6 5 years ago

This thread scares the he!! out of me.

You've replaced twelve ICs and two other components without having a clue what the problem is?????

And, since D25 is reading exactly as it should, it seems pretty obvious to me that you should put the soldering iron down and get professional help.

Or, heck you're close enough now, why not just replace all the rest of the ICs on the board. After you've finished, send this guy a pile of cash with your board...

www.coinopcauldrin.com

--
Rob Anthony
Pinball Classics
http://LockWhenLit.com
Quality Board Work - In Home Service
borygard at gmail dot com

#7 5 years ago

Funny Rob. I had the same reaction, but the OP is pretty far into it right now...why stop?
Besides...neither of us want to see that board, right?

I'd still counsel comparing various measurements between two identical boards.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

#8 5 years ago
Quoted from ChrisHibler:

...Besides...neither of us want to see that board, right?...

Absolutely not. Note the link.

Quoted from ChrisHibler:

...I'd still counsel comparing various measurements between two identical boards...

Absolutely. It's always a good idea to compare to a known working circuit before pulling out the soldering iron.

--
Rob Anthony
Pinball Classics
http://LockWhenLit.com
Quality Board Work - In Home Service
borygard at gmail dot com

#9 5 years ago

Actually Rob, several of the chips were replaced prior to the board coming to me. I don't have a logic probe, however I do have plenty of chips and sockets on hand.

I do appreaciate your input and help though, keep up the good work Rob Anthony, you have been a huge help.

#10 5 years ago

Hmm, well, Rob and Chris, you and I are on the same page.

I think there are still a few ICs that haven't been replaced on the board. Perhaps one of them will be it?

I've got a Y-adapter for my atx power supply that I use on the bench, so I can hook up 2 WPC MPUs side by side. I agree, invaluable. Stick a WPC test ROM in each board, and boot them both up!

I've found a real schematic is worth about 100x more than the PDFs floating around for this sort of thing. One of the later, legal sized booklets, that folds out.

#11 5 years ago
Quoted from robgo777:

Actually Rob, several of the chips were replaced prior to the board coming to me. I don't have a logic probe, however I do have plenty of chips and sockets on hand.
I do appreaciate your input and help though, keep up the good work Rob Anthony, you have been a huge help.

Go spend 20 bucks and get one. You can do so much with them!

I have this one, and use it all the time:

http://www.mcmelectronics.com/product/72-190&green=9D124A8C-6C62-557F-B6E1-406F47277293

#12 5 years ago
Quoted from robgo777:

Actually Rob, several of the chips were replaced prior to the board coming to me. I don't have a logic probe, however I do have plenty of chips and sockets on hand.
I do appreaciate your input and help though, keep up the good work Rob Anthony, you have been a huge help.

Ahhh. Well socketed ICs certainly change things since they can be swapped without risking damage to the board.

Logic probes are very inexpensive and an invaluable tool for troubleshooting pinball boards. I use mine far more than an oscilloscope.

--
Rob Anthony
Pinball Classics
http://LockWhenLit.com
Quality Board Work - In Home Service
borygard at gmail dot com

#13 5 years ago
Quoted from johnwartjr:

Go spend 20 bucks and get one. You can do so much with them!
I have this one, and use it all the time:
http://www.mcmelectronics.com/product/72-190&green=9D124A8C-6C62-557F-B6E1-406F47277293

Thanks for the link John, I will put an order in for one along with some more 74LS244s

Any recommendations on some documentation that covers what to look for with a logic probe? My experience is limited to replacing at the component level. I do have the ability to test two boards side by side on my bench.

BTW, removing chips is pretty quick and easy with the P808KIT!

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