(Topic ID: 261801)

Stars MPU won't boot with PF lamp connectors plugged in


By QuietEarp

5 days ago



Topic Stats

  • 12 posts
  • 2 Pinsiders participating
  • Latest reply 19 hours ago by Quench
  • Topic is favorited by 1 Pinsider

You

Linked Games

  • Stars Stern Electronics, 1978

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There have been 2 images uploaded to this topic. (View topic image gallery).

IMG_5702 (resized).jpg
IMG_5701 (resized).jpg

#1 5 days ago

Hi,

I was doing some work on my Stars. I had it playing well for a few weeks. Then it wasn't getting 12 volts DC on the rectifier board (TP3). I corrected that issue (Bridge Rectifier) and now the game will not boot up. It gave me 4 flashes. I found that if I unplugged J1 on the MPU the game would boot. J1 feeds the lamp driver board and displays.

I find that if I connect J1 on the MPU but unplug connectors J1 and J3 on the lamp driver which feed the insert lights on the playfield, the game boots up. If either of these are connected to the lamp driver board, I only get 4 flashes on the MPU.

Where should I be looking from here? What is causing this?

I have a Weebly MPU and the rest is vintage.

Thanks!

#2 5 days ago

An update. I swapped in the Lamp Driver Board from my Mata Hari and the game worked fine.

Stars LDB in Mata Hari works fine.

So I swap the boards back to their original games and everything in Stars works fine?!

What could this mean? Repin board and connectors J1 and J3? Seems weird that these connectors would cause booting problems as they only drive the controlled lamps?

I would still like to know why that happened because I didn't like that and it could happen again. Any ideas?

#3 5 days ago

The MPU board 6821 PIA chips can be determined as "faulty" during the power on self test if one of their port A pins are shorted to ground or something else.
U10 port A controls the switch matrix, lamp board and display numbers.
U11 port A controls the display digits.
All the lamp and display signals go through MPU J1.

If by chance when you were diagnosing your 12 volt issue did you disconnect J4 from the lamp driver board and accidentally reinstall it off by one pin or upside down?

The only way I can see J1 and/or J3 from the lamp driver board to cause this issue is if there's a shorted lamp socket to a switch on the playfield - but even that's a bit dubious.

Quoted from QuietEarp:

What could this mean? Repin board and connectors J1 and J3?

Don't reterminate your connectors for this issue. The error condition was a short circuit, not open circuit.

#4 5 days ago
Quoted from Quench:

If by chance when you were diagnosing your 12 volt issue did you disconnect J4 from the lamp driver board and accidentally reinstall it off by one pin or upside down?

I don't see how I could have as it has the key in the connector housing.

Thanks for the suggestion though!

#5 4 days ago

Update!

When I did the whole board swap thing between Mata Hari and Stars I did not fasten the board with the screw so the boards were floating.

Game works fine with lamp driver board floating. When I screw the lamp board in creating a solid grounding path with all lamp board connectors plugged in the game does not boot.

If the board is screwed in and the connectors to the PF lamps are unplugged (J1 and J3) the game does boot up.

Any thoughts with this new info?

#6 4 days ago
Quoted from QuietEarp:

If the board is screwed in and the connectors to the PF lamps are unplugged (J1 and J3)

Which one is it? J1 or J3?

Does disconnecting J2 and J3 (playfield and cabinet switch matrix harness respectively) from the MPU board make any difference?

Do you have the earth braid at the base of the head connected to the cabinet earth?

#7 4 days ago

If J1 or J3 is plugged in the game does not get past 4 flashes. Both must be unplugged for game to boot.

Disconnecting MPU connectors J2 and J3 does not make any difference. I also tried only disconnecting one of them at a time and there was no difference.

Earth Braid is connected to cabinet.

#8 3 days ago

What happens when:

(a) When the lamp driver board is not screwed down, are all feature lamps on the playfield working properly?

(b) Everything is connected but you don't screw the lamp board, how much voltage do you measure between the grounded metal shield in the head and the GND test point on the lamp driver board?

(c) At the lamp driver board with J1 and J3 connected and screwed down but disconnect J4 from the lamp board?

(d) All four connectors are connected to the lamp board and screwed down but you disconnect all other playfield connectors (i.e. MPU-J2, SDB-J1, SDB-J5, Rectifier board-J1)

(e) All 5 displays are disconnected

#9 3 days ago

Quench, thank you for your help! I have seen you in these types of threads diagnosing things and the help you provide is very much appreciated.

Now the game seems to not boot when the grounding screw is in the lamp board no matter if J1 or J3 is plugged in on the lamp board. This was definitely different yesterday.

a) yes, all feature lamps work properly when lamp board is not screwed down

b) 0 volts

c) Game boots

d) 4 flashes on MPU

e) 4 flashes on MPU

#10 3 days ago

Ok, two more if you don't mind. What happens when:

(f) Everything's connected and screwed down, but disconnect J2 from the lamp driver board (LDB)

(g) Everything's connected and screwed down, but disconnect J4 from the solenoid driver board (SDB)

Can you retry (b) from above but take measurement in both AC and DC voltage?

If possible please post a clear picture of the J1 connector at the MPU board clearly showing all wire colors and same with J4 at the lamp driver board.

#11 2 days ago

(F) 4 flashes only
(G) 4 flashes only
(B) 0 volts AC and 0 volts DC

IMG_5701 (resized).jpgIMG_5702 (resized).jpg
#12 19 hours ago

That second picture showing J4 on the lamp driver board, you can see nine red resistors on the board.
With the machine OFF, and your multi-meter set on resistance mode, black meter lead connected to ground, how much resistance do you measure with the red meter lead on the left side leg of each of those nine resistors?

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