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(Topic ID: 266143)

Stern MPU 200 woes


By pinheadpierre

6 months ago



Topic Stats

  • 19 posts
  • 7 Pinsiders participating
  • Latest reply 6 months ago by pinheadpierre
  • Topic is favorited by 3 Pinsiders

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#1 6 months ago

I have been taking advantage of being stuck at home to work on a Seawitch project. The game is a real roach in its present state. First, I am trying to get it working fully/reliably.

When I first put it up on legs and connected everything, it worked except that after about 10 minutes, the left flippers would die. Given that the wiring for the flippers was total crap (poor soldering, frayed wires, etc), I thought I would start by putting in all new flipper mechs with fresh wiring on molex plugs.

After changing out all four flippers, I tried playing again. It played fine for about fifteen minutes except that I noticed that the lower right pop and the right sling weren't working. I shut it down, lifted the playfield and found that the coil stop for the sling had cracked in half, allowing the coil to fall out and pull off one its wires.

I fixed the sling with a stop from one of the old flipper mechs and tried firing the game up again. This time it made a couple garbeled sounds and then...nothing. No sounds (never the normal "bong" boot sounds), no led on the MPU. I have some playfield lights on, but nothing else.

Any suggestions?

#2 6 months ago

Is there any acid damage on the mpu? Do you have an nvram installed and the battery pack removed?

#3 6 months ago

Did you check your fuses on the rectifier board under the playfield?

#4 6 months ago

Sounds like the coil wiring could have shorted to something when it fell out, definitely pull fuses and check them with your meter. If getting no led at your mpu, i think that means you're getting no 12v at the mpu. I would check with your meter at the test points on the mpu to make sure you're getting 5vdc and 12vdc.

#5 6 months ago

Thanks folks. I never looked closely at the bridge rectifier (or much else for that matter since I planned on replacing most everything eventually). I didn’t even bother testing the bridge rectifier since it looked so bad. I remembered that I bought one right after I bought the game a long time so but never put it in. Planning on replacing the connectors, too. I’ll be doing that now and then checking back in. Here’s a couple pictures of it:

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#6 6 months ago

It's almost impossible to tell if a rectifier has failed from a photo. Did you test the fuses? In particular, F3, F4 being out would cause the game not to boot.

#7 6 months ago

I did test the fuses. They were fine. I’ve got the new bridge rectifier soldered up. Tomorrow I will repin the connectors and put it back together.

Might not be the problem, but since I was planning on doing it anyway, I figured why not eliminate it as a possible source of or contributor to my issues.

#8 6 months ago

That's a great place to start. That power resistor has definitely seen better days!

#9 6 months ago

Okay. So I replaced the bridge rectifier, including repinning the connectors. Here’s a couple pictures of my work.

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#10 6 months ago

Now the game boots (hooray!), but when I start a game, there are multiple issues.

First, the flippers work but none of the other coils are firing.

Second, it’s acting like there’s a switch matrix error. I’ve never dealt with a classic stern before and don’t know how they work in this regard. I’m familiar with Williams system 9 wherein switch errors were usually a blown transistor on the mpu. Is Seawitch similar? What do you folks think is going on here?

#11 6 months ago
Quoted from pinheadpierre:

Okay. So I replaced the bridge rectifier, including repinning the connectors...

Good work, but quick point of order, it's not a 'bridge rectifier board." It's a rectifier board, which includes 3 bridge rectifiers on it

How many bongs are you getting now at start up?
Hiw isn't acting like a switch matrix error? Will it go into switch test mode?

#12 6 months ago
Quoted from TheLaw:

Good work, but quick point of order, it's not a 'bridge rectifier board." It's a rectifier board, which includes 3 bridge rectifiers on it
How many bongs are you getting now at start up?
Hiw isn't acting like a switch matrix error? Will it go into switch test mode?

Thanks for the terminology correction.

I get 7 bongs at startup. (Normal, right?)

The switch matrix type error is that it scores points and registers a drain upon activating a playfield switch.

I downloaded a pdf of the manual and skimmed it. I’ll read it more carefully later tonight.

I was able to go into the solenoid test. The only coil that fired was the knocker.

I also got into switch test mode and tested every switch on the playfield. All registered correctly (except the pop noted below), so now it doesn’t seem like a matrix issue.

When I tested the pops, the top and left pops register fine. The right pop does not register. I cleaned the switch for the right pop, wedged it shut and tested for continuity. The switch blades are making good contact but still not registering. That’s the only switch that failed the switch test.

In summary, no playfield coils except the flippers. All switches seem fine except the right pop.

#13 6 months ago

I also just checked voltage on all five test points on the new rectifier board. They were all good.

#14 6 months ago

I’m wondering if maybe one or more of my new trifurcon terminals is not making good contact? Not sure that would explain anything except the non-existent coil action, though. Wishing I had an actual printed schematic now. (Not that I’m good at reading them, but at least I’d stand a better chance than with my downloaded pdf version.)

#15 6 months ago

Am I reading correctly that the solenoids should get somewhere around 43v dc through a blue-white wire at pin 6 of J1 on the playfield harness connector to the rectifier board?

#16 6 months ago
Quoted from pinheadpierre:

Okay. So I replaced the bridge rectifier, including repinning the connectors. Here’s a couple pictures of my work.[quoted image][quoted image]

Good work on repinning connectors. The "E" holes in the rectifier board are meant for the wires to be soldered in the hole for a more ridged connection.

#17 6 months ago

Check the 1 amp slow-blow (i think that's the rating, it's usually labeled) fuse under the playfield, it probably blew. It's usually located near the flippers.

Can you put the game in switch test? There's a test button on the inside of the coin door that allows you to run through the tests for coils, lamps, displays, switches, etc. Make sure all drop targets are up and there's no ball in the outhole. Take note of which switch number (if any) is showing on the display. They're listed in the schematics.

#18 6 months ago

She has risen! (Pretty much) After replacing a couple suspect connectors and the 1amp slo blo under the playfield (which tested fine at the beginning of this process but must’ve blown at some point mid-stream - thank you frunch for getting me to recheck it), it is back up and running.

The right pop is intermittent, which is odd. I’m crossing my fingers that rebuilding it will solve that problem. We’ll see.

Also, the first time I drop a four bank, I get an extra ball. That seems too easy. Glitch or default setting? I’ll have to read the manual more thoroughly.

Thank you all for the help!

#19 6 months ago
Quoted from PinballManiac40:

Good work on repinning connectors. The "E" holes in the rectifier board are meant for the wires to be soldered in the hole for a more ridged connection.

Almost forgot to respond to this! I wondered if that’s how it is supposed to work. I’m guessing you’re supposed to lay them out like I did but tuck one and underneath through to the other side? I did it the way I did because in the heat of the newbie moment, I couldn’t see how feeding the wire through would allow the solder to fill that wide of a hole. Now it maybe makes more sense. If I have to do this again someday, I’ll try it.

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