Stern magic boots and plays, everything scores as it should. Sound board is disconnected, pretty sure I have an issue with sound, but that's the next problem. Current problem is no feature lights. Rectifier voltage is good, and (obviously) F1 on the rectifier is good. I've rebuilt the connectors to the lamp driver with no change in performance. Switched lamp drivers with another classic Stern. Known working board does not drive feature lamps, and the board out of the Magic performs fine in the other game. So, I think I'm down to tracing wires, but I'm not sure what to trace. Suggestions greatly appreciated!!
Cheers!
Bob

With just J2 plugged in, picking up ground from the Rottendog rectifier, I get 6.2 on both pins. And TP1 on the known good driver board is 5.06.

I got some truly bizarre readings from the bare wire, so I changed the battery in my DMM and tried again, after getting a 1.6 reading from a AAA battery. Picking up ground from the rectifier board, I put the red lead on the bare wire next to the 'G' lamp at the top of the playfield, which is where I believe the blue 6V power wire connects. Reading is solid 6.25, just like TP1 on the rectifier.

Switched out the MPU and everything is working, other than a few lamps being out. Pretty sure that's just bad bulbs. So, the next step (after a played a couple of really cool games on Magic) is...What am I looking for on the MPU?

THANKS!!!

My working board is an Alltek ver L, so I'll have to check compatibility. In the meantime, I swapped U10 and U11 on the Magic MPU board with the same result.

Thanks!!

No joy on lamp test...I'll go get the logic probe.

My inexpensive logic probe appears to have given up the ghost, showing no readings on any pin, anywhere.

I found a couple of clean PIAs (they were still in original, static free packaging) and switched them out. I also switched my Alltek 6800 with the Magic 6800. The game using the Magic 6800 boots and plays perfectly (a 77 Stern Pinball) while the Magic boots and plays just fine, except there are still no feature lights. I'm thinking we are down to wiring/connector issues...but I yield to people WAY smarter than me...

Borrowed a logic probe. Picked up power at TP1 on the MPU. With the game in attract mode, MPU J1 pins 11, 13-19 are all pulsing.

Thanks barakandl, all connectors have been rebuilt, and the chips are all socketed with machine strips. I certainly believe it could be related to connectors and/or sockets, but could you narrow it down for me a little more? As in which pins I should be focused on?

Thanks!!

I'd previously switched out a known good LDB, with no change in performance on the Magic. The game I put the Magic LDB into worked fine, feature lamps and all. All test voltages on the LDB are good. I've ordered the schematic, but don't have it yet, so don't know exactly where to test...

In the meantime, I tested connectivity from the leg of U10 and U11 PIAs to the solder pads on the backside of the board. I found a couple of cold joints and reflowed the solder on both. No change.

OK, with the game in attract mode, pin 1 on all 4 decoders is low, but not pulsing.

I went back and double checked everything on the MPU. Pin 11 must be the stern strobe, as pin 8 does not have a wire attached. I miscounted positions earlier. J1 Pin 11 is low, not pulsing. 12 - 19 are all pulsing. Just a side note, I rebuilt the connectors one wire at a time to assure no crosswiring. From the condition of the pins, all dark gray, I'd say the game had never been repinned, so I'm reasonably confident the wiring is correct. What is the next step?

WTF?
U10 pin 19 is high and pulsing, so are both sides of R78, AND J1 pin 11 (which was low and not pulsing previously, maybe reflowing the solder did something after all) All with the logic probe getting power from MPU TP1, which tested at 5v.

LDB decoder pins all still low and not pulsing, logic probe drawing power from LDB TP1, which also tested at 5.

I really appreciate your help!!...and once again have no idea what the next step is.

OK, either the game or the logic probe is haunted...TP1 on the MPU tests at 5.02, TP1 on the LDB is 5.05. With the logic probe drawing power from the LDB, the decoder pin 1s all show low and no pulse. If I draw power from the MPU, they are all pulsing. And here's an interesting twist: Just for giggles, I probed U10 pin 19 again. Pulsing AND momentarily, many of the feature lights came on, with the bonus multiplier lights remaining lit.

Alligator clip from braid to GRD test point did not work...More to come.

Thanks again for all the help and tech tips/theory!! I've done a dozen or so classic Bally/Stern resurrections, but never, ever had any lighting problems beyond a stubborn lamp here and there.

OK, picked up a couple of 8x32 screws and made sure of good contact between the LDB and the mounting brackets. Still get different readings on the logic probe depending on how I am getting power/ground between MPU and LDB. Through switching boards in and out, I don't see any issues with the backbox plate or connections between it and the ground braid or board mounting brackets.

Key readings:
MPU J1 pins 11, 13-19, pin 1 on LDB decoders, and LDB J1 pin 5 all probe low/pulse and MPU U10 pin 19 probes high/pulse when powered from the MPU TP1, and all are low/no pulse when powered from LDB TP1. In all cases I'm getting ground by clipping to the board's mounting bracket.

The bare ground wire to the feature lamps
shows 6.2 on the DMM, and I can get the feature lamps to flash when they are grounded with a jumper. (I forgot to answer that question earlier. Grounding the bulbs has always worked.)

Just for giggles, I put the alltek board in again. Game boots up and goes into attract mode. Most of the feature lamps are working. I put the game in lamp test and several non-working bulbs came on with a slight touch, so I'm assuming any remaining lights not working are bulb/socket issues. I reprobed the decoder pins on the LDB. Using the board ground TP, they show low, but the pulse light is also locked on. Getting ground from the ground braid, they show low/pulse.

And, by the way, USPS says the schematic is in transit to the destination, so hopefully this year...

Schematic has arrived, though without an MPU schematic. I've at least verified that the LDB pinouts for J1 are correct. But then, the plot thickens. I fired it up again and watched the attract mode for a minute or so. It's seems OK, but some of the patterns seem more random than they should. I double checked that I had the dip switch settings right to play Magic. They are correct, so I started a game. Hmmm....interesting that I start with 5X bonus, and when I roll over a bonus advance, the multiplier drops, then starts adding value to the inlane, and eventually repeats the pattern. WHAT is going on here?

I checked connectivity, and so far, everything going to the playfield from the LDB is correct based on the schematic and has good connectivity, including the Multiplier, Bonus, and inlane lamps lamps. For now, I'm going with the 'haunted' theory.

Yes, with the alltek board, but not all lamps light. I haven't catalogued what's working vs not working to try and establish a pattern yet. That's Likely the next step...

OK, again, just for giggles, I switched in a known working lamp driver. So an Alltek board and known working LDB produce the same result, in that some lights work, but among those that do work, they are not correct based on game play. That is, just as described above, I start each ball with 5X bonus, and hitting a bonus advance takes me to 4X, then 3x, 2x, then the inlane values go from 8000 to 6000 to 4000. The last three bonus advances up to 10K do not light any lights. Once I get to what should be 11K bonus, the cycle repeats once, up to what would be a max 19K bonus. Scoring is correct on all of the features. To further complicate matters, all drop targets down advances the bonus multiplier as it should.

The backbox lamps that are associated with the J2 connector all work correctly - tilt, high score to date, player up, etc. The problems are all on LDB connectors J1 and J3.

I've now traced and checked connectivity based on the schematic, and it's all good. However, I know that schematics are notoriously incorrect on wire color and location, and I'm starting to wonder if incorrect wire location isn't at least part of the problem. Some of the wires have been 'unbundled' as evidenced by the kinks where there used to be zip ties, and maybe a previous owner moved some things around based on the schematic. However, the fact that all drop targets down lights the multipliers in the correct order would tend to refute that theory. The weirdness continues...

Here's where I'm at:
The following feature lamps do not work in lamp test or during game play:
M and G at top of playfield
M, G, I, C at standup targets on the side of the playfield
1K-10K bonus lights
Spinner 400 lights on both sides
Lower left special
Shoot again

Switching LDBs does not change performance, and the LDB that was originally in Magic will run properly in another classic Stern. In my view, this rules out anything on the board itself. I'm currently running the game off of an Alltek MPU, and I have triple checked the dip switch setting to make sure they are correct. In game play, where I would expect a game to start with 1000 bonus lit, 5X is lit, and bonus mutilplier counts DOWN as bonus advance targets are lit. See above for more detail on the..um...unusual light behavior.

With the lamps in test, all of the non-working lamps will work when grounded. But as I was testing this, I made an interesting discovery. I was working with a relatively short jumper, so I tested all of the non-working lamps I could reach while clipped to the left rail. They all worked when grounded. I then moved over to the right hand rail to test the lamps I could reach form there. None of them worked. WTF? Picked up a longer jumper, and they work fine when grounded to the left hand rail but not when grounded to the right. I thought I'd found the problem, loose nut on the right hand rail to ground, but tightening that up did not change the result of the grounding test. So, I at least appear to have some kind of grounding issue, possibly among other things. And once again, I'm stuck on how to proceed, other than tracing ground wiring and looking for anomalies...

Corrected the rail grounding problem, which was caused by a corroded bolt, and this did not change performance. The mystery continues.

Any other thoughts appreciated, I'm completely stumped.

Yes, I have the schematic from Marco, though MPU schematic was not included.

Already done. The wire locations match the schematic. There are a few wires not noted on the schematic, but everything that is on the schematic matches the game, and connectivity from pin to lamp is good. Agree about the ROM, but everything else works fine. The MPU is an alltek, and the dip switch settings are correct. Odd indeed.

Hmmm...tried to respond earlier, but don't see that post. Maybe it's just me.
I am traveling, and will check again when I get back home, but these pins were all pulsing when I last checked them.

MPU J1 pins 11-19 are all pulsing There is no wire coming off of pin 8, but the pin is pulsing.
LDB J4 pins are all pulsing.
LDB U1-4, all pins are pulsing, pin 22 on each chip is pulsing much slower.

With the game in score display test, all of the non-functioning lights that have a known good working bulb and socket work when I ground the corresponding SCR gate.

As I learn more about this, I begin to wonder if there's not a wire (or wires) out of place that is causing some kind of signal confusion. That is, some binary combinations are repeated, and some are never created....grasping at straws...

Thanks Barakandl...but, um, I'm clueless about what that actually means.

Cody - I realized I failed to answer another question you'd posed. Some of the non-working lamps are driven by each of the chips on the board. For example, none of the bonus lamps work. 1, 5, and 9K are driven by U1, 2, 6, and 10K by U2, 3 and 7K by U3, etc.

I've been reading posts, Clay's guide, schematics, and staring at the game all afternoon. If I've tried multiple combinations of MPUs and LDBs with the same result, and both LDBs work fine in another game, doesn't that point to wiring or connectors?

Done for the lamp driver, but the MPU schematic was not included in the paperwork from Marco.

And no worries at all, John. This game has a mysterious lighting issue. Other than that, it's a really beautiful game with classic Stern play, and a keeper!

And, just to add a little more to the mystery, while the backbox controlled lamps all work, they are scrambled, too. Player 4 remains lit, even if you only start a 1 player game, and the # of players lights change with each ball. I remain stumped.

Unplugging the connectors on the right side of the mpu has no impact.

The MPU is an Alltek, and it runs another classic stern just fine. Given the finnicky nature of the PIA, I'm reluctant to handle them unless absolutely necessary.

Before switching to the alltek, I'd exchanged the PIAs on the original MPU with no change in performance, then switched in two new ones, still in their original anti-static packages. Again, with no change in performance.

At this point, everything I've tested says this should be working correctly, and I've matched wire locations with another working game. Known working boards in the game. Still not working correctly. Still stumped...

It's a miracle! I cooked up a crazy idea. Thought I'd pull one of the wires on J1 and see what that did to the lights, and see if I could create a variation in the problem and see some kind of pattern. So I pulled the wire to pin 17. None of the feature lights worked, even after I hit the bonus advance a couple of times. So I plugged that wire back in with the power on and noted that I had some bonus lights on. WTF?

Powered down and back up, started a game, and all of the feature lamps are now working. So, my conclusion is that through all of my poking, prodding and wiggling of connectors, J1 17 on the LDB never got seated right until just now, thus the game was getting no binary codes for the bonus lamps, and duplicates of the codes for other lights.

Connectors, connectors, connectors.

And very special thanks to Cody Chunn, Barakandl, and L_Satan, who offered tons of help and patience!