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I have a 7603 that I'm trying to do basic check-out on. But I only have one 7000-series plugin (a 7A17).
The 7A17 can operate in either vertical or horizontal slots, but the 7603 does not produce a trace at all without a horizontal plugin (the manual confirms this is the case, but doesn't say why). So I have confirmed that the horizontal works, but cannot test the vertical.

Questions:
Why is the trace disabled without a horizontal plugin? A vertical is not required...
Can I temporarily "hot wire" the horizontal slot, so that I can test the vertical slots with my 7A17 ? Looking at the schematic, it's not clear which pins are involved in disabling the trace when the plugin is missing.

Thanks!
Pete

The horizontal plugin provides the sweep signals. Without that, there's no trace.

Barry - N4BUQ

On Sat, Feb 8, 2025 at 08:40 AM, n4buq wrote:

The horizontal plugin provides the sweep signals. Without that, there's no
trace.

No, there would be a "dot" that does not move horizontally. Lack of "sweep" is different from lack of "trace" (in my mind).
Note that the 7A17 is a very basic plugin - it is just a simple amp that drives either the X or Y amp of whichever slot it's plugged into. When I plug in the horizontal slot (with no vertical), there is a dot on the screen. If I apply an AC signal to the input of the 7A17, then I get a horizontal "sweep".
But with the 7A17 in a vertical slot, the CRT is blanked.
SO, one or more of the signals on the horizontal slot is blanking the CRT.

Pete

Get Tektronix Circuits Concepts books on basic of oscilloscopes.

On eBay find any 7Bxx horizontal plugin

Jon

One can find PDF copies of the Tektronix "Concept" and "Measurement" books
on TekWiki:




DaveD
KC0WJN


On Sat, Feb 8, 2025 at 11:40 Jean-Paul via groups.io <jonpaul=
[email protected]> wrote:

Get Tektronix Circuits Concepts books on basic of oscilloscopes.

On eBay find any 7Bxx horizontal plugin

Jon

It just occurred to me that the REASON removing the horizontal plugin blanks the CRT is (probably) because a normal "sweep" plugin needs to support retrace blanking, and (I'm now thinking) that the retrace blanking signal defaults to "blanked" when nothing is plugged in.
SO, if look at a typical sweep plugin schematic, I can find the pin that is used for retrace blanking...

Pete

It's looking like it's pin A1 ("gate").
In the 7A17 (which unblanks the CRT, but does NOT provide a "sweep"), pin A1 is tied to +5 coming in from pin A8.
In a typical sweep plugin (such as 7B50), pin A1 is driven by the plugin's Gate output circuit.
I'll try it...

Pete

Not only does the Horz plugin in provide the sweep signals it ALSO provides the positioning as well as blanking disable. In the absence of signal the dot is there but it is pulled off the side of the screen. Left side if I remember correctly. The drive signals also provide blanking disable. So the dot might be in the middle of the screen but the blanking circuit is keeping the beam current driven off.

Zen

Confirmed: In the horizontal slot, connecting pin A1 (Gate) to pin A8 (+5V) un-blanks the CRT, and a dot appears near the center of the screen.
Now it is possible to plug in ANY suitable plugin into either of the vertical slots, and get a vertical trace.

Pete