9100B with smoked zener

[Richard.Wilder]

Hi All,
I recently got back to work on my non-working 9100B that I bought several years ago. I found a smoked zener diode on the ROM address driver board. It measured 0 ohms before unsoldering it then broke while I was extracting it. Problem is the color bands are burned beyond recognition. Anybody have an idea what Vz or Vcol is? Vcol = -(15 - Vz).
Thanks for any assistance!

Richard
   
   

[Bushcat]

Does this help?

https://ia802201.us.archive.org/24/items...ematic.pdf

[Richard.Wilder]

Thanks but no. The rom address driver board is not included in those schematics.

[teenix]

I was trying to see where -Vcol went but I couldn't find it on the schematics. Maybe it could provide a clue to the zerer voltage.

cheers

Tony

[Bushcat]

(04-18-2023 04:34 AM)Richard.Wilder Wrote:  Thanks but no. The rom address driver board is not included in those schematics.

First page, board 12, plug 1 connections don't help?

[Richard.Wilder]

Thanks Tony & Bushcat,

Here's where Vcol goes. It's the array of transistors that are part of the multi-layer ROM board.
That voltage doesn't appear on board 12 plug 1. It provides the voltage & current to drive the columns and for design purposes needs to be something less than -15 volts.

For some reason I can't attach pictures.
Look on the Tony Duel schematic labeled "Address Drivers 09100-66567" for the references to Vcol.

[teenix]

Not much to go on looking at the circuit.

Maybe someone with one of these can get a number from the matching part and it may be listed somewhere.

Or (probably a long shot) if someone has a dead machine, perhaps take the part off the board and measure the breakdown voltage using a voltmeter, adjustable DC supply and series resistor.

cheers

Tony