Re: 7603 weirdo inverted Z axis
There are some ways you can narrow down the problem before tracing thetoggle quoted messageShow quoted text
z-axis control circuits:
1. Does the readout intensity control also operate backwards?
Its signal goes directly to the readout board which then drives the
input to the z-axis amplifier in parallel with the normal intensity
signal so it bypasses all of the z-axis logic.
2. Plug-ins can also adjust the beam intensity. If you have a 7B92A
timebase, what does its intensity control do?
3. Is the leading edge unblanking working correctly when a fast pulse
edge is observed?
I checked my 7603 and with a 7B53A timebase, about 1/2 division at 50
ns/div (25 nanoseconds) is unblanked before a fast pulse edge. With a
faster timebase like a 7B92A, 1 full division at 50 ns/div (50
nanoseconds) is unblanked before a fast pulse edge. Oddly enough a
7B50A also unblanked 50 nanoseconds before the fast pulse edge so I
assume it shares more in common with the faster timebases than the
As far as tracing the circuit, the z-axis amplifier is straightforward
but the z-axis logic shown on schematic 2 gives me a headache. I will
have to break out Clipboard CAD to figure out exactly what is suppose
to be happening there. I do see one thing however:
The sweep gate rises at the base of U99B to redirect the current from
the intensity control through the emitter of U99B to the collector.
The intensity is controlled by this current. If the -15 volt
connection to the intensity potentiometer is open, then the current
would *increase* as it is turned counterclockwise lowering the
resistance between the wiper and ground reversing its operation. The
intensity control range would also be affected but this might not be
very noticeable if the grid bias was adjusted.
So instead of checking to see if the intensity potentiometer is
connected backwards, check to see if the -15 volt supply is present at
the intensity potentiometer and that the wiper actually moves between
0 and -15 volts as the control is turned through its full travel
range. Note that -15 volts is suppose to produce the highest
intensity and 0 volts is suppose to produce the lowest intensity.
On Fri, 22 Jan 2016 20:18:20 +0100, you wrote:
Among other issues with this 7603 were the Z axis operation, it seemed