Restoring a VT50 (VT52 actually) .

Josh Dersch derschjo at
Sat Dec 23 11:51:34 CST 2017

On 12/23/2017 5:34 AM, Mattis Lind via cctalk wrote:

> 2017-12-23 13:32 GMT+01:00 Mattis Lind <mattislind at>:
>> 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
>> board.
>> 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
>> well.
>> It would be very nice if you could tell me the location of the PROM chips
>> as well.
>> /Mattis
> 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
> at all.

I've been tinkering with a VT52 at the museum.  I found that the sockets 
for the PROMs are of poor quality and were not making good connections.  
This may not be a problem in your case, but it's something to take a 
look at if you haven't already.

- Josh

>>>          cheers,
>>>            —FritzM.

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