I really enjoy working on pinball machines. With the help from people here I have a nice working Flight 2000. I’m now fixing up a Trident. I’ve rebuilt two rectifier boards. I’ve repaired a solenoid driver board (both the regulator side and the solenoid driver side.) I have even fixed a badly corroded lamp driver board.

But when it comes to the MPU reset section I can never get one to work. I’ve replaced sockets, IC’s, transistors, switching diodes, zener diodes, diodes, etc. Still no flicker and no flash.

Why is the reset section so mysterious? It seems to me it should be pretty cut and dried. If your reset don’t work check the voltage here, then check continuity here, if that checks out then check the voltage here, etc, etc. I admit there are a lot of components in the reset section but it shouldn’t be that complicated to diagnose.

I’ve looked at PinWiki, Flipperwinkel, and others but someone needs to write an article showing step by step how to diagnose a reset section.

Bob

You guys are very helpful. And I’ll check your suggestions tomorrow. It’s because of this kind of help that I got my first pinball machine running. And I really appreciate your input but you have missed the point of my rant.

I have been reading The Bally Pinball Repair Procedure Manual. It is helpful but it doesn’t go into reset circuit. What I’m saying is there could be a manual similar to this for just the reset. IE - check for 9 volts at U22 pin 42 – if yes, go to U13 pin 52 – if no, check trace from TP9 to Q7. Etc, etc.

I’m sure that you guys that repair these boards all the time must have a certain procedure that you use to check the circuit. I doubt you just shot gun a bunch of components and hope it works – (that’s my procedure, and it ain’t working)

Maybe if all you board gurus got together and made a step be step procedure for diagnosing a bad reset circuit it would really help us amateurs. Perhaps a PinWiki for just the reset circuit.

Don’t get me wrong, the help here on Pinside has been tremendous. I read every post concerning the MPU’s and I have a notebook full of notes that I use all the time. But sometimes I’m just not sure I’m going in the right direction.

Thanks

Bob

Thanks Andrew, That's exactly, what I'm looking for. It starts on the bottom of page 28. I didn't know it was in there. I haven't read the entire manual yet. Unfortunately my printer is not working so I'll have to make notes and run from my computer to the shop to do the testing.

Cody, I know how you feel. This is my second MPU - Andrew had to fix my first one. He does great work but I'd love to fix just one on my own.

Thanks guy, wish me luck.

Bob

Maniac, I'll try to answer some of your questions here but for more history and photos of this board here is another post I started a couple of months ago:

https://pinside.com/pinball/forum/topic/trident-mpu-100-still-not-booting

The board had some corrosion but I've seen worse. I cleaned it up and repaired the damage.

The LED stays lit until I short pin 40 - 39. Then I get 6 flashes on the bench test.

I did not replace the 555 - but it looks pretty good.

I did ohm out the traces anyplace I worked on the board. I'm new to this and not that confident in my work. I did have a short under the J4 header but I fixed that now.

Please, when you have time, check my other post above.

Thanks you and everyone for all your help.

Bob

Thanks Andrew, I'm sure you and all the others are correct that my power supply is holding me back. I'll try it tonight if I have time - got some yard work to do first.

For the future - could I use a computer power supply's 12 volt connected to a driver / regulator, then make a jumper cable to connect the MPU's J4 to that?

Thanks

Bob

I was concerned about the size of the power supply - just looking at the size of a pinball transformer compared to a power supply.

I been looking for a replacement transformer for my Trident - it's dicey on the high voltage side - held together with silicone glue. But it would make a good bench power supply.

Thanks cfh, I do have 5 volts at U9 pin 40. I'm hoping my bench power supply is the problem. As soon as I can I'll put the board in the machine and see if that works.

Thanks

Bob

This thing is getting to me now. I installed the board into the machine and got 6 flashes right off. (I didn’t see a flicker). Second try I got all seven flashes and heard some clicking under the play field. (I think it was from the drop targets) I was super stoked. I tried it a few more times then I got solid on. I checked the voltages - TP5 = 5 volts – TP2 = 14.5 volts and TP3 = 22.5 volts.

I unplugged it and was about to leave when I realized I didn’t screw the board down (don’t know if it would make a difference) I screwed it down and tried again – solid on. I shorted pins 40 – 39 and I got seven flashes. Tried it a few more times and sometimes it would boot and other times not.

This tells me A) I still have problems and B) my power supply ain’t cutting it. And it’s really difficult to work on it when it’s in the machine.

Any suggestions?

By the way I only connected J4. I haven’t installed the remaining headers yet.

Thanks

Bob

IMG_2481.JPG

I had a little time to work on my MPU tonight. Out of about 10 tries I got it to flash 6 times once. The rest I just got solid on.

I removed the board and the mounting brackets. The bracket looked close but didn't touch the 5 volt line. But to be sure I cut a notch in the bracket anyway. I also polished mounting tabs to insure a good ground.

Then I added a jumper wire to ground as suggested.

I really don't think this was the problem but I'll re-install it tomorrow and find out. At least I feel I made it more bulletproof.

Thanks

Bob

IMG_2487.JPG

IMG_2491.JPG

Today I re-installed the modified brackets and MPU. Flipped the switch and got 6 flashes - a long hesitation then the seventh flash. (even the coin door clicked). I tried it again and got solid on. 6 or 8 more tries and still only solid on.

I worked on another project for about 30 minutes then tried again. 6 flashes - again, 6 flashes. About 6 or 8 tries and I get 6 flashes.

Also I never see a flicker. As soon as I flip the switch I get solid on then it starts flashing. And the LED is new - from Radio Shack but it is new.

I hate when stuff like this happens - either be broke or be fixed! But broke one time and working the next is driving me crazy.

Anyone have any suggestions what to try next?

Thanks

Bob

Maniac, I do have a sight delay between first and second flash - but no flicker. I'll try to make a video but I'm not too good at making videos. And my video camera sucks.

Freeplay, I have already re-built all the connectors and pins on all the boards except the light driver board and sound board. I have replaced the capacitors on the driver / regulator board (as well as connectors) and I replaced the regulator transistor. I replaced the fuse holders, rectifiers, and diodes (as well as connectors) on the rectifier board. So I'm pretty sure all the power to the MPU is fine. I suspect my power supply is not providing the correct power because I never got any flashes until I put the board into the machine. I'm working on a different bench power supply.

Baraka, I'm pretty sure I have a problem with the zero crossing. I looked at R16 and R113 - they look OK. I have 22.5 volts at TP3. But I haven't checked U10 yet. I'll check it with a logic probe as soon as I can.

I tried booting it again today - first try I got 6 flashes (no flicker), then solid on, the 6 flashes, then solid on. I tried about 8 times and every other time I'd get solid on.

Today's questions - why don't I ever get a flicker? And why does it boot up only every other time?

This just drives me nuts!

Thanks

Bob

Thanks Freeplay,

I'm pretty sure I'm getting 6 flashes, the few times I got the 7th flash the coin door coil kicked in. I think that only happens on the last flash.

I have 22.5 volts at TP3 so I'm sure the 43 volts is there. U10 is new but the socket is not. It looked clean so I didn't change it. I did tone out all the pins from the chip to the solder pads. U14 and the socket are new.

Hopefully tonight I'll have time to check the zero crossing with a logic probe.

What's strange is it only seems to boot every other time. It's 6 flashes, solid on, then 6 flashes, then solid on. ?????

Thanks

Bob

Baraka, R113 and R16 look OK. TP3 is 22.5 V. But U10 P18 is showing 5.04 V and no pulsing. I also checked U14 P4 and got the same. I haven't checked anything else yet.

Freeplay, I hate changing 40 pin sockets - worse job ever. But if I continue to have problems, I'll have to change them. That's about the only thing left to change.

Thanks

Bob

You must like going to the Dentist too. Do you have a method for removing sockets? I have a decent de-soldering tool but it don't remove all the solder on the socket side and I end up cutting the pins off. Heating them one a time and pulling them out - just like pulling teeth.

Thanks

Bob

Baraka, From the schematic I made a list of voltages to check on U14

P-14 = 4.9
P15 = .25
P9 = .25
P10 = 4.5
P5 = 4.5
P4 = .25

Do these voltages look right? Anything else to check?

I hope to have time tomorrow to check them.

Thanks

Bob

zero cross.JPG

It's difficult for a fat old fart like me to work inside the back box but I managed to get these readings:

All from U14

pin 14 looking for 4.9 v - I got 5.18
pin 15 looking for .25 v - I got .32
pin 9 looking for .25 v - I got .39
pin 10 looking for 4.5 v - I got .72
pin 5 looking for 4.5 v - I got .70
pin 4 looking for .25 v - I got 5.04

Numbers look close until you get to pin 10. U14 is new. Could R18 have something to do with this problem?

Thanks

Bob

Thanks Ed,

I get 0.34 volts at pin 16.

I think I got another U14. I find the smaller IC's harder to insert into the socket. (actually I find all IC's hard to insert) But I may have messed it up when I put it in.

I was planning on changing it but I'll have to remove the board. That's why I wanted to get my new power supply test rig going. Also I'm going to get a transformer and bridge to test the zero crossing on the bench.

Thanks

Bob

I removed the MPU from the machine and hooked it up to my new test rig. I'm getting the same results from the test rig that I was getting in the machine. About half the time I get 6 flashes and other times I get solid on.

Also I never see any flicker. As soon as I flip the switch the LED goes on. I thought I was just not seeing the flicker in the machine but it doesn't flicker on the bench either.

Anyone know what's happening?

Thanks

Bob

I just replaced the U14 with another new one - Pin 1 is just over 5 volts - so is pin 2 but pin 3 is 0.0.

I'm going on memory here but I'll recheck again tomorrow.

Thanks

Bob

Faz, I’m glad you are enjoying this thread. Hopefully, you, me and others will learn something in the end. But right now it’s driving me up the wall.

I have my new bench tester working – even have a 25 volt transformer working for the zero crossing circuit. Seems to work as well as being in the game. Unfortunately the MPU still shows the same problems.

Last night I changed the U14. Tried it a few times and still don’t get the last flash. I gave up.

Today I went out to check some voltages. I turned it on and got 7 flashes. I thought I miss counted so I tried again – 7 flashes. About 3 –4 times I got 7 flashes, then back to 6 flashes. Then I checked the voltages on U14 (pretty much the same as when it was in the game.

pin 14 looking for 4.9 v - I got 5.8
pin 15 looking for .25 v - I got .42
pin 9 looking for .25 v - I got .42
pin 10 looking for 4.5 v - I got .64
pin 5 looking for 4.5 v - I got .53
pin 4 looking for .25 v - I got 5.79

I also checked pin 16 and got .43. And I checked pin 1 and got 5.92.

The new chip is failing at the same place as the other chip – at pin 10. Could both chips be bad?

I also noticed several times while checking voltages that it would sometimes re-boot on its own. This board is very flaky. I’ve changed all the sockets except at U9 and U10. Do you think those sockets could be causing this problem?

Thanks

Bob

I finished installing the remaining header pins last night. I hooked it up to my bench tester and I get flicker and 6 flashes every time. I checked the voltages at U14 and got pretty much the same results as before. I also looked every where I worked for a short but didn't find anything.

I pulled the U14 and checked resistance:

pin 1 - 2.55 k
pin 2 - 7.7 m
pin 3 - 0 to 5 ohms
pin 4 - OF
pin 5 - 277.3 ohms
pin 6 - OF
pin 7 - .570 m
pin 8 - .5 ohms
pin 9 - 6.33 m
pin 10 - 272.4 ohms
pin 11 - 1.00 m
pin 12 - 21.0 m
pin 13 - 5.5 m
pin 14 - 113.0 k
pin 15 - 6.32 m
pin 16 - 17.5 m

I have no idea what this means - hopefully someone will and can help.

Thanks

Bob

Also I noticed this thread is getting a bit long - should I start a new thread?