Restoring a VT50 (VT52 actually) .

Mattis Lind mattislind at
Sat Dec 23 06:32:24 CST 2017

2017-12-23 10:08 GMT+01:00 Fritz Mueller <fritzm at>:

> Hi Mattis,
> > On Dec 23, 2017, at 12:08 AM, Mattis Lind via cctalk <
> cctalk at> wrote:
> >
> > Anyhow, the VT52 boards are dead. … The terminal uses 4 pieces
> > of 256 by 4 bipolar PROMs for a total of 512 bytes of microprogram.
> > Has anyone dumped the contents of these so I could verify them?
> I have a restored VT52.  Taking a peek, I see these PROMs are socketed, so
> I can pull mine this weekend and give them a read for you no problem.
> I actually had a lot of trouble with a flaky oscillator when I was working
> through my VT52, but it sounds like your’s is going fine if you are
> observing the whole timing chain including video sync?

Yes, the oscillator seems to work. But it is a pain to work with the VT52
since the print set has very little information. Where is the component
list? I cannot verify which PROM should go into what location. And the damn
boards doesn't have any component designator anywhere, nor is there
anything on the component placement info in the print set on the data path

The PROMs in my machine are: 23-124A9, 23-125A9, 23-126A9 and 23-127A9. Is
this the same as your VT52? Apparently there is an earlier PROM set as

It would be very nice if you could tell me the location of the PROM chips
as well.


>         cheers,
>           —FritzM.

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