Re: Tektronix 7854 Digitization Issue

Kyle Rhodes

I've had some success! Adjusting the Good Sample Flip Flop seems to be the
ticket. In B5 on page 4-50 of the service manual it has one adjust R102 by
reading some voltages to start with -- this did not work for me. But,
attaching the scope as starting in step 'L', I was able to see the waveform
and I adjusted R102 until the signal looked good and triggered well.

However, I think I was a bit over-zealous in putting the covers back on, as
while the waveform acquires much better now, I am seeing some strange
behavior at the end of the waveform -- namely, it tends to zero out for
0.5-1 divisions. I suspect I can fix this with some more careful
adjustment of the GSF signal pot, as I don't recall it doing this in the

I started from the beginning of the Z-axis calibration on 4-47. My initial
voltage was 30V high, so I got that taken care of.

Though, in B4 "Adjust Z-axis Transient Response) on 4-49 I had some
trouble. I could not for the life of me get C150, R150, C155, and R155 to
do much of anything. They all already were pegged as well, so not sure if
someone else tried in the past too. Not sure if this affects digitization
stuff at all, or just analog display? I need to look at the schematics in
more detail...

Furthermore, it appears I need to look into calibration, as when I was
paying close attention to signal amplitudes and periods during testing, I
noticed some things are off.

And, shall I say, this scope is a beast! What incredible engineering went
into it....


On Tue, Sep 17, 2019 at 10:49 AM Albert Otten <aodiversen@...>

Hi Raymond,

You are right! I misinterpreted the function of the GSF (a little bit
stupid since the vertical signal I referred to is not at all involved
here). Apparently the blanking signal is included already by the Z-axis
controller and not a separate signal to the Z-axis amplifier.
Well, this will be a relief for the OP.

On Tue, Sep 17, 2019 at 03:21 PM, Raymond Domp Frank wrote:


On Tue, Sep 17, 2019 at 01:53 PM, Raymond Domp Frank wrote:

Of course, I don't remember exactly which one...
It's the GSF (Good Signal Flip-flop) trimmer (U102) on the Z-axis board
13). See description of Digitiser Control Logic > Bus Control > Internal
Acquire Mode, page 2-61 in my manual (070-2874-01), Jan '82. Also, see
2-8 on page 2-122 and are F,G-2 in dwg 21.


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