5 Dec
1999
5 Dec
'99
1:29 p.m.
Upon the date 02:16 PM 12/5/99 -0500, John B said something like:
-----Original Message-----
From: Allison J Parent <allisonp(a)world.std.com>
-- snip --
>???? Why? The scope is an enclosed system that
would be hard pressed to
>emit high voltages back into the system it's hooked to. It's not like the
>HP9100 in that respect. For the RM503 to do that the HV lead would have to
>fall on one of the input lines! As I remember the series 8 Display scopes
>were driven off a pair of D/As and some single bit output to blank the
>beam. If you have something different I'd like to hear about that.
I agree with Allison. Without knowing exactly the mods done by DEC that you
mention below, I'm still assuming the output of the D/As is connected right
into the SO-239 style front panel input connectors. In that case, the input
circuitry is isolated from any HV. The inputs go directly to the vertical
and horizontal amplifier tube grids (the 6DJ8's) after passing thru their
respective attenuator switch assemblies.
Three D/As. 1 12 bit for x, 1 12 bit for y, and 1 3 bit for intensity. When
the transformer went in this RM503 it raised the regular voltages throughout
the scope to 500+ volts... in some places over 1000. That was present right
Ouch. I hope bypass capacitors and some coupling caps haven't had their
dielectric damaged. Most of the ceramic caps and poly caps have ratings of
500 and 600 volts DC respectively and 1KV is pushing or exceeding their
surge voltage rating.
through to the input. I am protecting the D/A
converters as I don't need the
PDPs taking major beatings in the future. All the supplies inside the scope
(-100,100,250,85,-3000 were going nuts). The other RM503 I have has the same
problem. I am going to put an isolation transformer on every RM503,RM560
scope I get to solve the problem ahead of time.
The other one has same problem? Interesting coincidence or possibly a
common failure mode of this scope. I *was* going to put a benchtop style
503 on my 'hunt for' list as it looks to be an excellent X-Y scope for my
bench but I'll do some further thinking on that I guess.
The 8 Display controllers have the intensity option :-) (for spacewars of
course). The AX08 (XR option) and the 34D (standard) had a 3 bit intensity
D/A output for the scope. The RM503s were modified by DEC for intensity
control.
That manual you said you have, is it from DEC or Tek? I'm curious about the
mods. If you have a vanilla Tek manual like I have you can see that there
are a pair of binding posts on the back of the unit which may be labeled
"CRT GRID" and "GND." The GRID connection goes directly to the CRT
grid
through a 0.001 mfd capacitor.
Now if DEC has done some fancy stuff to the 'scope by intrusively
interfacing the PDP8 display controller directly to the deflection
amplifier circuits in some manner then yes, I'd be leery of potential
damage to the PDP circuits. Same for the intensity modulation (aka Z-axis
modulation) circuit.
Regards, Chris
-- --
Christian Fandt, Electronic/Electrical Historian
Jamestown, NY USA cfandt(a)netsync.net
Member of Antique Wireless Association
URL: http://www.antiquewireless.org/