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+--- Thread: 9100B with smoked zener (/thread-19824.html)
9100B with smoked zener - Richard.Wilder - 04-17-2023 11:45 PM
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
[attachment=11989]
[attachment=11990]
RE: 9100B with smoked zener - Bushcat - 04-18-2023 03:49 AM
Does this help?
https://ia802201.us.archive.org/24/items/bitsavers_hp91009100_28364269/9100B_Schematic.pdf
RE: 9100B with smoked zener - Richard.Wilder - 04-18-2023 04:34 AM
Thanks but no. The rom address driver board is not included in those schematics.
RE: 9100B with smoked zener - teenix - 04-18-2023 05:21 AM
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
RE: 9100B with smoked zener - Bushcat - 04-18-2023 08:30 AM
(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?
RE: 9100B with smoked zener - Richard.Wilder - 04-19-2023 12:17 AM
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.
RE: 9100B with smoked zener - teenix - 04-19-2023 01:27 AM
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