Pinball Nirvana Home Page

Go Back   Pinball Nirvana Forums > Real Pinball > Maintenance & Repair

Maintenance & Repair Discuss and offer tips on real life machines.

Thread Tools Search this Thread
Old 12-07-2011, 12:56 PM
pb1592 pb1592 is offline
Inserted Coin

Join Date: Oct 2011
Posts: 10
Credits: 11,290.95
Thanks: 4
Thanked 0 Times in 0 Posts
Rep Power: 0
pb1592 is on a distinguished road
Default Strange display problem on Williams System 11b (Taxi)…


I’m having a very strange problem with my displays on a System 11b Taxi machine. Here is the situation:

1) Purchased the machine used and noticed that the upper main display was beginning to outgas and flicker, most likely due to its age. Still functioned adequately and got better as the machine warmed up.

2) I performed the mod on the high voltage section of power supply, swapping in new 39k resistors at R1 and R4 and 91V zener diodes at ZR2 and ZR4. (Note: I’ve done this mod to four other machines and it has worked flawlessly.)

3) After swapping R1 and R4 there was no change and everything still worked as it did before. After swapping ZR2 and ZR4 however, the upper main display would not work at all. I figured the lower voltage (91V vs the original 100V) wasn’t sufficient for the already failing (outgasing) upper display.

4) HERE is where it gets strange: I decided to reverse the mod and put the original 100V diodes back in ZR2 and ZR4. When I did this however, the upper display still would not work…

5) After playing around and double checking solder connections, I noticed that if I completely removed ZR2 from the board and put nothing there, then the displays worked perfectly. This worked with ZR4 being both either the 100V or 91V diode. The displays were dimmed as expected when ZR4 was a 91V diode and ZR2 was not present.

So my questions are…

1) Does anyone have a logical explanation behind this? My knowledge of this display circuit is very limited.

2) Is this causing an over-voltage of the whole display circuit?

3) Is it safe to keep it this way? No other mods were made to the power supply or display circuit. The only change at this point is fresh new 39k 1-watt R1/R4 resistors and a missing ZR2 diode in the high voltage circuit of the power supply board.



Last edited by pb1592; 12-08-2011 at 08:40 AM.
Reply With Quote


11b, display, system 11, williams

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Pinball Titles I've Played: Vpin/Real Life (LONG POST) GravitaR General Pinball 18 04-17-2015 03:25 PM
Phone Chats With Harry Williams JonPurpleHaze Articles from Russ Jensen 0 11-07-2014 05:43 PM
A Visit With Harry Williams JonPurpleHaze Articles from Russ Jensen 0 11-05-2014 07:54 PM
Williams Sorcerer Score Display Problem RiffWiz Maintenance & Repair 2 01-30-2011 03:54 AM
Subtle problem with Williams System 7 (Black Knight) SQLGuy Maintenance & Repair 3 01-23-2011 03:06 AM

All times are GMT -4. The time now is 08:51 PM.

Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Template-Modifications by TMS
Credits System provided by vBCredits II Deluxe (Lite) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Shoutbox provided by vBShout v6.2.15 (Lite) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.