On 2026Feb 2,, at 11:00 PM, Rob Jarratt <robert.jarratt(a)ntlworld.com> wrote:
>
> I forgot to reply to this one. Thanks Brent.
>
> Of particular interest is the description of how the monitor board is supposed to work in the VT180 TM at page 6-102. When I have time I will check it carefully, I think there may be clues about Q414. Interestingly the intro says that horizontal section is not intuitively understandable from an examination of the schematic and it is a likely candidate for failure because of high stresses in the components.
I forgot some th-of-op was also included there, and then found it again tonight in another document:
vt100.net <http://vt100.net/> has a work-in-progress html version of some VT100 Technical manual:
https://vt100.net/docs/vt100-tm/ <https://vt100.net/docs/vt100-tm/>
There doesn’t seem to be a document date there but Chapter 4 has that th-of-op section on the Elston monitor:
https://vt100.net/docs/vt100-tm/chapter4.html <https://vt100.net/docs/vt100-tm/chapter4.html>
Section 4.8
Neither of course has the schematic, but notably these th-of-op sections reference component IDs that match the PCB & your RE'd schematic, and the small th-of-op diagrams do show Q414 as PNP.
The T403 pin numbers there differ from your labeling as Digital/Elston viewed it as 6-pin with 1 & 5 absent, rather than 4-pin.
Your pics show what appear to be some date codes from 1979.
The vt100.net <http://vt100.net/> website is aware of other field printsets from 1979:
https://vt100.net/manx/part/dec/mp-00633-00/ <https://vt100.net/manx/part/dec/mp-00633-00/>
but they also cannot find them.
So it does appear that, in addition to the Ball monitors, there were two versions of the Elston monitor for the VT100:
- one from 1979 with PNP HOT,
- one from 1982 modified to NPN HOT (along with other mods) (per MP00633_VT100_Schematic_Feb82.pdf)
Double-checking with the pics, your schematic looks correct to me regarding the HOT circuit.
Looks like the board could be modified for NPN with 1 ~ 3 trace cuts depending on how one went about heatsinking the HOT.
Or use the search specification selectors on sites like Digikey or Mouser to find an adequate hi-V PNP power transistor.
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Dear administrators,
Once again Gmail users appear to have been disabled. Could you please help
and re-enable me and others who have been affected. It is only 3 or 4
months ago when this happened last. It would be nice if this could be fixed
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Thanks and best regards
Tom Hunter
I bought a reel of paper tape at an office supply shop today.
It was in their 'bargains' room and is marked
NCR
SYSTEMEDIA
01-6388181
Telex 888634
PTI
Made in England
It cost me £0.50. I think they had two more reels. it's age is indicated by
having a London phone number that was made obsolete 30 years ago.
However, what surprises me is that it's 17.5 mm (0.69", 11/16") wide. This
seems too narrow for 7-hole tape and too wide for the tape used for
telegrams. Is it for 5-hole tape ?
Hi all,
I have a controller card (i'll elaborate later in the message) for an
ICOM 3712 8" floppy drive unit. However, i do not have an FD3712 system
to interface to it!
With Shugart style floppy emulation essentially a solved problem, i'm
wondering if similar has been done for the FD3712. As the computer side
of the floppy interface is just a parallel interface, and all the disk
geometry wizardry happens on the FD3712, i'd assume a lot of the
difficulty of Shugart floppy emulation is essentially a moot point. So
the question is, is there a project already existent to replace the
FD3712 unit with an emulated (raspberry pi based?) alternative?
I'm asking the question as i have an RCA Microboard bus CDP18S646
combined Centronics Printer interface and FD3712 floppy interface. It
also came with an MBZ80 z80 based CPU card, and i'm putting 2 and 2
together and gathering it was likely the two were used together. If i've
every got a a hope in hell of booting anything, solving the media
problem is quite important.
Cheers,
Josh Rice
As posted previously I am trying to repair my VT100 and I am having trouble
with the Monitor Board. The one I have does not match the available printset
(PDF p54 of this
https://bitsavers.org/pdf/dec/terminal/vt100/MP00633_VT100_Schematic_Feb82.p
df). My VT100 appears to match the older
https://bitsavers.org/pdf/dec/terminal/vt100/MP00633_VT100_Mar80.pdf
printset, but it doesn't cover the monitor board.
My monitor board looks as follows
https://rjarratt.wordpress.com/wp-content/uploads/2023/12/img_20231221_11223
3.jpg and the two big transistors on the left appear to be incorrect parts
possibly from a previous repair attempt before I got the VT100.
Does anyone have a previous revision of the VT100 with a Monitor Board that
matches mine? If so, would you be able to photograph it please, or tell me
what parts are installed for the two TO-3 transistors on the left? Better
still would be if anyone has the printset for this version of the monitor
board.
Thanks
Rob
