Restoring a VT50 (VT52 actually) .
mattislind at gmail.com
Sat Dec 23 07:34:58 CST 2017
2017-12-23 13:32 GMT+01:00 Mattis Lind <mattislind at gmail.com>:
> 2017-12-23 10:08 GMT+01:00 Fritz Mueller <fritzm at fritzm.org>:
>> Hi Mattis,
>> > On Dec 23, 2017, at 12:08 AM, Mattis Lind via cctalk <
>> cctalk at classiccmp.org> 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.
I did some more research into the terminal after I put the christmas ham
steak into the oven and christmas rice pudding on the stove.
There were nothing going on at the microprogram outputs. All high. It
turned out that the CE input for the PROMS was high for ALL banks!
Impossible! A 7400 at E34 was not doing well. After replacing that there
are some life in the microprogram and I have some random klicks from the
key klick relay. But still not working as it should. So more interesting
fault finding ahead! 20+ years sitting in a cold attic probably is not good
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