TEMPEST: Diode on DAC08

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Hi,

Just finished a repair on a Tempest board-set and have a question with regards to a diode soldered onto the original DAC between pins 2 and 4 - cathode to pin 4.

It appears to be a factory mod and was wondering if I should attach a diode to the replacement.

Looks like a 1N914??

Thanks

Jeff
 

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Later vectors, such as Gravitar, have the protection diode added to the PCB layout. (See CR4 below).
Many, if not most, Tempest do not have this added mod to the DAC. Later games evolved the architecture which BZ and Tempest originated.

DAC08_diode.jpg


Note that the online Tempest cocktail schematic shows the diode with no designation. :)

DAC08_diode_Tcktl.jpg
 
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I know on the Cine and VB analog switchs (LF13331) diodes are in place to prevent damage caused by one voltage getting to the switch before the other (i forget which )......
 
Should this mod as well as the cap mod on the MC1495 be performed on all Tempest PCB's?
 

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Should this mod as well as the cap mod on the MC1495 be performed on all Tempest PCB's?


You see the diode and that extra cap on some Rev A and Rec C boards. But not all of them, so even then it varies.

They removed them for Rev D (which is what the majority of Tempest boards are). So I don't think they are critical.
 
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