Another scope 7854

Joe Laffey

Hello all,

Well, I am now the proud owner of another scope I don't need... a Tek 7854.

It came with a 7A18 (70MHz dual input) and a 7B53A (100MHz dual time base).

The 7A18 has some issues. Channel 1 seems fine, but Channel 2 has a lot of noise on it (need to check the exact value, but the line is about 4 times thicker than Channel 1). It also seem to have all of its attenuator values off by around one click of the switch (not exactly). All waveforms have much greater vertical amplitude then they should. The readout display is correct based on the switch position.

I tried cleaning all the basic switches and pots, but I have not disassembled the cam based switches on the attenuator controls. I was wondering what special tricks there were to dealing with those. I am guessing one of the contacts is dirty/bad.

I will try to use the Open/Closed table for the attenuator and the amount of increase vertical scale to determine which contacts are bad. I just need to sit down with the unit and the service manual and see what I can discern. Any info is appreciated.

The scope also seems to have trouble triggering cleanly off Channel 2. I will occasionally see a glitch waveform. I do not see this on Channel 1. Also the glitches go away if I toggle the Channel 2 polarity switch to invert mode. They also go away if I use DC Offset (Option 06) mode on the 7A18.

I am guessing I should start with the cam switches, but do those trigger glitch criteria ring any bells with anyone?

Also, what is the fastest setup I can get with this 7854? The 7A24 with its 50 Ohm 400MHz inputs? And the 7B85 ? Just trying to figure out the ideal plugins to look out for. I'd like this to be my fast scope, possibly supplanting the 2465 (300MHz).

What happens if you try to run the 1GHz plugins in the 7854? Are they just limited to 400MHz or what?

This thing is pretty amazing considering the date of manufacture. Of course it was over $30k in today's dollars...


Joe Laffey
The Stable
Visual Effects

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