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(Topic ID: 278738)

Unknown jumper on System 1 MPU

By RDBowers

3 years ago



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  • 4 posts
  • 2 Pinsiders participating
  • Latest reply 3 years ago by RDBowers
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#1 3 years ago
OP
 
RDB

RDBowers

Pinside member

CA Uxbridge, ON

3y 36,650 119 21

Any idea why someone would install a jumper between pins 3 and 7 of IC Z29. According to the manual it is described as SN7405N IC-Hex Inverter - OC - T.I.

From the looks of the soldering job, it looks like it was done after it left the factory.
PXL_20201003_165152371 (resized).jpgPXL_20201003_165152371 (resized).jpg

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#2 3 years ago
 
TK

Tuukka

Pinside member

FI Lempäälä

5y 78,350 1,762 16 18

That is to defeat slam and ball roll tilt switches.

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#3 3 years ago
OP
 
RDB

RDBowers

Pinside member

CA Uxbridge, ON

3y 36,650 119 21

Thank you @tuukka. That jumper will be removed and cleaned up next time I have the MPU board out.

1 week later
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#4 3 years ago
OP
 
RDB

RDBowers

Pinside member

CA Uxbridge, ON

3y 36,650 119 21

Thanks for the input. I have come across two references to this mod.

The first is in Leon Borre's web page on PinWiki on "Repair of Gottlieb System 1 CPU Board". He notes installing the jumper to test the CPU then suggests leaving it.
https://pinwiki.com/wiki/index.php?title=Leon_Borre_Gottlieb_System_1_Repair

The second is in Clay Harrel's web page on "Gottlieb System 1 Pinball Repair from 1977 to 1980" under section "2g. Permanently Defeating the Slam Switch". I like this implementation better because the the jumper is soldered across the leads on the capacitor C2 and not pins 3 and 7 on IC Z29.
http://www.pinrepair.com/sys1/index.htm#slam

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