VT52 is back in service!

Chris Zach cz at alembic.crystel.com
Wed May 13 20:59:41 CDT 2020

Well, I put the VT52 back together, tightened all the bolts, plugged it 
in, turned it on and enjoyed the silence. I can just barely hear the 
transformer hum but that's about it.

Hooked it up to my PDT11/150, booted up RT11 and the display is 
perfectly crisp and clear. Ran space invaders to check it out, no bugs 
or errors and the screen updates perfectly.

Glad I got this working again. I'll take a look at that transistor, I'm 
almost 100% positive the switching transistor is either leaking or going 
bad. Either way I'll order a transistor when I have some time and put it 
in eventually to see if it works. But to be honest the new regulator is 
a thousand times better than the original discrete logic system.

So moral: If your VT52 goes nutty and the screen becomes a blur try 
checking all of the voltages. An errant -12v will make the screen 
unreadable at -15v and I'm guessing oddness on the other voltage levels 
will do similar things as well. And don't leave it on for days, that's 
probably what pushed the transistor over the edge, but I'm guessing it 
has been crummy for awhile which is why I heard all that noise in the 
high voltage circuit.

I feel like I accomplished something today. Thanks everyone for the help 
and thoughts in getting this old girl to work again...


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