1 Aug
2014
1 Aug
'14
2:33 p.m.
Hello, all,
I am in the midst of restoration of a very old (1964-ish) electronic
calculator called the Wyle Laboratories Scientific Model WS-02. This is
a transistorized electronic calculator that uses a magnetostrictive
delay line for register storage, and a CRT display for showing the
working registers and memory registers. The CRT is driven by
sine/cosine signals to generate fully-formed stroke-style digits. I
don't know if it's magnetically or electrostatically deflected...is
It could be either, your comments give suggestions both ways...
A defleciton yoke -- coile around the CRT flare -- would genrally imply
magnetic defleciton. But I'd expect 4 wires to the yoke (2 f0r vertivcal,
2 of horizontal), not 'a couplke of wires'.
If the thing draws the digits by some kind of vector technique (as
oppsoed to scanning a raster), then electrostaitc defleciton is more
likjely. It is a lot easier to set the requirede deflecion by chearging
the (small) capaitance of the defleciton plates than by controllig the
current rhrough a coil -- often you need a fairly high votlage to the
output amplifiers in an electromagnetically deflected vector monitor just
to ocercome the back emf of the yoke coils when you change siad current.
But if there si a genuine flyback transformer (as opposed to some kind of
HV supply) then that implies a raster display, which is likey to be
electromgnetically deflected.
there any easy way to tell? There are some coils
around the neck of the
CRT, but they are not as large as I'm used to seeing on CRT's of this
size (8").
The question that I have is that I want to test out the power supply
circuitry to make sure that all is healthy there. I have removed the
logic module from the machine (the logic module contains all of the
calculating and display generation logic, and comes out as a unit). I
have also disconnected the video driver board. The connector at the
back end of the CRT is unplugged. There are a couple of wires that go
to the coils around the neck of the CRT, but they are connected to the
video driver board,which is disconnected. The high voltage connector
from the flyback is still connected to the CRT.
Is there any other conenction to the video PCB (which presumably includes
the flyback/NV trasnformer). The reason is, of course tht if the video
PCB is not gettign any power then the HV supply can't be operational so
there is nothing to worry about.
IMHO there is little risk to the HV supply if you run it without a load.
Taht correspodns to a blank screen and few machines are damaged by that.
But if the unit uses the capacitance between coatings on the insdie and
outside of the CRT flare as a smoothing component, then if the outer
coating is not earthed it, too, will get up to a high votlage and may
flash over to soemthing. Something that you dont' want gettign zapped.
So make sure the CRT earthing is in place and connected.
waht I would do, if at all poisble, is to desocnect the CRT driver board
completely, make sure it can't be getting pwwer. Then sort out the LV
pwoer supplky. When there is OK, conenct up the CRT driver _with the CRT
base conenctor fitted ot the CRT_. That way there will be beam current if
there should be, and everythign will be OK.
At this point, I've traced out the main logic voltages (+12, -12) and
a -30V supply that are used throughout the machine.
I want to slowly bring up the power supply with a Variac and monitor
the voltages and ripple to see if the power supply is still healthy.
However, I'm concerned about having the high voltage supply connected to
the CRT without any other connections on it? Could the high voltage
supply be hurt because it may be missing signals it needs to oscillate
properly? Could this hurt the CRT? I don't know enough about the way
There are only 2 (simple-ish ways to damage a CRT. One is to break the
glass (drop it, drop soemthign on it, damage a pin seal when conencting
the base, etc). The other i to seriously overvotlage the ehater. The
heater is liekly to be 6.3V in a machien fo this age. Giving it 10V wis
not good, but it probably wont' burn out. Anything more and it might. But
unlike an IC, it will fail slorly, if you watc hthe hater when power is
applied and it applearst oeb a lot brighter then you expect, or it's
whiterr that normal, turn off the power and invetigate.
I think it's unlikely, too, that running the HV supply without an inpu
would dmage it. It's possiblem I guess, and the only way to be sure is to
see the schmatics, which I asusme you don't have.
So, I'd try to isolate the video section complete,y then run up the LV
supply on it's own.
-tony