I have an MPU-200 board from a Big Game I purchased about a year ago.

When I first tested the board with the original battery still attached it booted on the workbench (once).

I then removed the crufty battery and did a mild restore for the minimal battery damage. Unfortunately, once that was done all I ever saw again was a solid LED when powering up the board.

Since then I've replaced a couple of the sockets that were a bit sloppy and decided to shotgun replace all the components in the reset circuit. Unfortunately, when I did that I failed to realize that C5 was supposed to be polarized and the cap I had installed popped like a firecracker upon power up. I then replaced that cap with a polarized one but the game still goes to solid red led and stays there.

I ran through the following tests as noted in the pinwiki topic (http://www.pinwiki.com/wiki/index.php?title=Bally/Stern#MPU_boot_issues):

>>> Short pins 40 and 39 momentarily on the cpu chip; after doing so, see if the LED goes off.
* Nothing happens (LED stays on).

>>> An easy quick test for the reset section is putting your DMM on pin 40 of the cpu. It should read 5v, and in most cases if it does the reset is good.
* Testing P40 on the cpu shows 0.39v when powered on.

>>> Ensure that there's not simply a problem with Q2 or the LED itself (i.e. the board isn't actually booting up anyway, just with the LED locked on). A logic probe on pin 18 of the U11 6821 PIA will tell you if the LED signal is changing.
* Nothing happening on p18.

>>> Attach a logic probe to the output of Q5 - on power on, you should see this circuit start low and then go high approximately 50 milliseconds later. If it goes high immediately, at a minimum replace Q5, then Q1.
* Logic probe (on pulse mode, is this correct?) reads low on all 3 legs of Q5 when powering up and afterwards.

So I'm at a loss as to what to check next. I'll attach some good pictures in case someone can spot something I've fouled up.
I'd really like to keep this board in the game since it's in pretty decent condition overall (if it worked).

All help is appreciated.

IMG_4325 (resized).JPG
IMG_4321 (resized).JPGIMG_4322 (resized).JPG

IMG_4323 (resized).JPGIMG_4324 (resized).JPG

>>> Next put the probe on U9 pin 3, 36, and 37 to see if you get pulsing - these are all clock signals and you should see pulsing on all 3 pins. If you have an oscilloscope you can visually see the signals, or even on a multimeter, the voltage will show between 2.5-2.9 volts. If you see zero volts or 5 volts, your clock signal is bad. The CPU could be dragging down the clock. Remove U9 and see if the clock signal is now good. When clock signal is bad suspect U15 or U16. Also check C15 and C14. U15 is failed most often.
* U9 p3, 36 and 37 are all in range and pulsing.

>>> Check U9 Pin 2. This is the HALT line. You should see 5v, if not replace U9
* 5.1v at p2.

>>> Check U9 Pin 5. This is the VMA line. It is a pulsing signal and reads about 2.8v with a DMM. If incorrect first try a new U9. Next check U14D, U15C, U19B. U15 is the most likely IC to have failed.
* No pulsing at p5. 1.2vdc on the MM.

So I replaced U15 and U9. No change. Still reading .36v at U9 p40 and no pulse on p5.

How can I test U19, U14 as it suggests?

Tested and CR5 upper leg reads 5.8v and lower 5.2v.

R113 looks fine but I did find an errant leg I missed clipping that was bent over and likely shorting between C80 and CR5. Fixed.

I also tested L1 and L2 and they both have appropriate voltages on both sides.

I realized I have a working Bally AS-2518-35 board handy so I hooked it up beside my borked MPU-200 board on the bench to compare readings. The only difference I've found on the lower half components thus far (though I haven't been perfectly systemic with these tests, could have missed some things) are on R107. On MPU-200 (with LED on) it reads 5v on one side and 4.06v on the other. On the working -35 board (with LED off, cause it boots) it reads 5v on one side and 0.083v on the other. I'm assuming this difference is because it must be in the circuit that lights the LED? So not really a problem.

I feel like I must be closing in on the solution! Other test ideas?

First I'd like to thank you for responding so quickly and the diagram is fantastic as well.

So I think the Q5 issue was caused by this issue, which is also the short you note on your picture: "...I did find an errant leg I missed clipping that was bent over and likely shorting between C80 and CR5."

So I corrected that and now:
- Q5 reads 5v on both the front 2 legs, and 4.55v on the rear leg.
- CR5 reads 5v on both ends

Also in that circuit are R138 and then R140 I believe:
- R138 reads 4.55v on one leg and 0.38v on the other
- R140 reads 0.38v on one leg and 5v on the other

However, Q1 reads 0v on the front two legs, and 0.66v on the rear leg.
And TP6 reads 0.122v.

Okay,

CR5 reads 5.72v and 5.17v

Q1 reads only 0.039v on upper leg (matches R140 leg, I was mistaken before on the reading), 0 on lower leg, and 0.673v on rear leg.

CPU p40 reads 5.11v

LED remains solid on with no flicker.

I retested the cpu with my probe and it remains the same:

>> Check U9 Pin 5. This is the VMA line. It is a pulsing signal and reads about 2.8v with a DMM. If incorrect first try a new U9. Next check U14D, U15C, U19B. U15 is the most likely IC to have failed.

* No pulsing at p5. 1.2vdc on the MM.

I already replaced the cpu and U15, I might have replacements for U14 and U19, should I try that?

Yep, those pins are pulsing (still).

P2 is high, correct.

Which pins are the CPU address lines?

Edit: looks like pins 9-24 on U9.

No pulsing on any of these pins.

Whoops my bad. In my haste I forgot to remove the roms.

With the roms removed I have:

5v at pin 8
P2 and P40 are both high
Pulsing on P3, P37
Pulsing on all P9-P24 except P21 is low/no pulse (p21 appears to be ground).

U6 socket checked out (pulsing). Pluggedin the U6 ROM only, now the LED will flashed on and off continuously (doesn't stop after even 7 flashes). Major progress! Would this be expected in this case with only one ROM installed?

When pulling the other roms the top socket came loose so I'll go ahead and replace all the remaining ROM sockets (I had already replaced U6).

I had U7 in still. Pulled it and the first boot led stayed locked on. 3 subsequent boots and it flickers and flashes once and goes out.

Yes. Using pc power supply on the bench.

K, replaced the rom sockets and loaded all the roms and ram back up.

Boots solid led. Quick short between p39 and p40 on U9 and it gives me two flashes.

So I have one original socket left to replace at U13 so will do that and check the 5101 sockets traces for continuity.

I also have a spare set of 5101 chips I can try.

Sound right?

Good news!

I replaced the socket and installed fresh 5101 chips and I’m getting 6 flashes on the bench!

Thanks a bunch for all your advice. Was very helpful in determining how to approach debugging the dreaded “solid LED” issue.

I already installed the stronger 2K resistors (1W now) as part of the replacement parts list from GPE's site.

I haven't actually replaced the VR1 zenier diode yet, the original is still installed. The new ones are so small compared to the original I was worried it might be the wrong part.

I will replace it though - excellent advice. My Star Gazer sometimes fails to boot when I use the wall switch to turn on the plug, but if I then turn the game off and on with the cabinet switch it boots fine. Possibly also has the original VR1 on its MPU as well. I'll take a look.

I messed up earlier, I was confusing VR1 with V1. So I did replace VR1 with the rest of the reset components.

It currently measures 11.83v on one side and only 3.77v on the other.

I believe the component I used is in-spec:

component (resized).jpg

Thoughts?

Right. So I should just install the board in the game and see if it boots correctly there. If it wasn't -8c (18F) outside I'd be more inclined to step into the unheated garage where the game is currently setup and do that.

Okay, the good news is that the board boots fine in the game and the game plays almost perfectly.

A couple of issues I'm experiencing:

1. The controlled lamps (incandescant) all flicker horribly, all of them (when lit) with the same pattern.

2. The game plays fine but whenever the ball drains and it goes to do the bonus countdown the MPU resets/reboots. It's not always at the same instant either, sometimes it reboots as soon as the drain/trough switch closes, other times it gets a few seconds into the bonus countdown. The trough switch tests fine in test mode. It's not the trough coil either I tested the diode and it usually reboots before the coil would fire. And of course the coil fire fine when you start the game. Also, I've noticed it will often reboot when attempting to use the test switch on the coin door. The entire game plays perfectly otherwise.

Possible poor ground connection somewhere?

This has me really stumped.

Will check these out.

Can you clarify which connectors to remove? "Does the lamp flickering go away if you disconnect J2 and J2 from the MPU board? You can disconnect these connectors with the power on."

Okay, I did a bunch of testing today:

As a reminder, the game will play perfectly until you drain your ball, then it will reset at some point during the bonus countdown. If you score points but no bonus it will not reboot, it will launch the next ball perfectly. The act of counting the bonus is causing the MPU to crash/reboot. The only other thing that causes the CPU to reboot is using the Test switch on the coin door. If you press it rapidly it will also reboot.

All switches register correctly in switch test mode.

GI lamps read 6.7vac
Controlled lamps (incandescent bulbs that pulse about 5 times per second): 3.8 - 4.0vdc (pulsing)
Lamp board TP2 and TP3 read 5.34vdc solid.

There is 11 ohm resistance between cab braid and the backbox tin, 33 ohm between the lamp board TP1 / grd and bb tin, and 22 ohm between TP1 and the cabinet braid. Cabinet braid to the ground plug on the power cord reads 2.3ohms.

MPU Board
Tp1: 5.1vdc
Tp2: 13.4vdc
TP3: 23vdc
Tp5: 5.1vdc

None of these voltage readings waver much at all during gameplay and not at all when the MPU crashes and reboots.

I tried unplugging each of these separately and testing the game: J1, then J2, then J3 - no change.
I unplugged the sound board ribbon cables - no change.

***

I then remembered that I now have a spare AllTek board so I put that in the game. Game plays perfectly with the Alltek and the pulsing controlled lamps issue is also resolved.

So, it almost seems like the MPU-200 board is incorrectly pulsing the controlled lamps, perhaps a short between two pins on one of the sockets or something? This is very mysterious but at least now I know it is definately the MPU-200 board causing the issue. Suggestions?

Okay, reviving this thread since I've needed to pull this board off my "spare" pile and put it back into action.

I've re-jumpered it for my Star Gazer ROMs and the board is booting fine now, but exhibiting the exact same issues in Star Gazer as it was originally in Big Game, namely:

1. All controlled lamps (incandescent bulbs, btw) flicker continuously when game is started.
2. MPU board will reboot whenever a ball ends.

Keeping in mind this game was working perfectly with another MPU 200 I had in it immediately prior to installing this one.

Based on this suggestion I've gone through the checklist of tests that you prescribed in this thread (https://pinside.com/pinball/forum/topic/bally-playboy-random-resets-flickering-insert-leds):

Check following pins:
U19 pin 8 (should be pulsing): -->Low (0.16vdc)<--
U19 pin 9 (should be high): High (5.26vdc)

U19 pin 10 (should be pulsing): -->Neither low nor high (1.28vdc)
<--
U14 pin 11 (should be pulsing): High (5.27vdc)

U14 pin 12 (should be pulsing): Low (0.02vdc)
This then goes to U15 pin 4: High

"So you're getting no activity on the VMA (Valid Memory Address) signal from the CPU at pin 8 of U19.": -->Low<--

"There is a resistor (R136) below the CPU (U9). What does your logic probe indicate on each leg (left and right) of this R136 resistor?": -->No R136 on MPU200??<--

"Also what's your logic probe indicating at pin 5 of the CPU (U9)?" : Pulsing

"What resistance do you measure between":
pin 8 of U19 and pin 14 of U19: 2.7M, 3.6M
pin 8 of U19 and pin 7 of U19: 2.7M, 3.6M

From the MPU-200 schematic I was able to prove continuity of the Ø2 line from U9-P37 to R8, to R6, to U15 P11, P14. The resistance on R8 and R6 also check out.

Note that I also tried swapping out U9 and U19 for known working versions and no improvement was made with either swap.

Any advice on where to look next for the problem is appreciated.

Bingo! It turned out to be a bad socket pin (#5) on U9, which broke continuity between U9 P5 and U19 P10. Replaced the socket and problem solved.

Thank you sir, you are a god in this world!