Re: 7B80 sweeping off the screen

Albert Otten

On Sat, May 23, 2020 at 12:42 PM, <ik1zyw@...> wrote:

First of all, on the "+ sawtooth" output in the back of the mainframe, the
working 7B53A produces a down sloping negative signal, sweeping between -4.5V
(trace @left) and -5.5V (trace @right). Measured on the low-ish impedance
analog voltmeter.

OTOH the 7B80 produces an up going positive "+ sawtooth" signal between +1V
(theoretical left) and +10V (theoretical right). Its frequency follows
time/div changes. Trigger is honoured (no sweep in single-shot for example).

Which reading is correct?
Hi Paolo,

The 7B80 reading is correct. If you change the Hor Pos control you might notice that the signal is actually between 0 V and +10 V. Just checked this in my similar 7633 (with 7B80 and 7B53A) and the Calibration procedure also mentions that 10 V amplitude.

In addition to Roger's comments (if this is not already what he meant), note that you might also use the 7603 as ordinary 'scope with 7B80 in the Left bay and some 7A in the middle bay and the 7B53A as time base. Trigger the 7B80 externally with some Line frequency signal and set the 7B53A also for Line triggering. Now you can probe the 7B80 internal circuitry and display wave forms via the 7A module. (Of course this makes it impossible to probe the rhs of the 7B80 though.)



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