Re: Persuading a 7S12 to play nice with a 7934.

Albert Otten

The connection of the base to R593 is deleted.
It's strange. With a DMM I could not find a connection of 2N2907A-base to any other component in the neighborhood or a A/B contact. But then the pair of NPN transistors with their bases to the B7 and A16 inputs would be useless. Do I overlook something?

On Thu, Mar 25, 2021 at 09:00 PM, Albert Otten wrote:

The solution with reduced value of R693 seems to have disadvantages also,
otherwise Tek would have done so I think.
That might be the reason that P600 has been introduced to enable/disable
interdot blanking. In the open position the PNP 2N2907A is shut off
completely. In the closed position the situation is as before. (I avoid
Q690/Q694 numbering.)
The next version of P600 is wired differently. When closed it it ties the
base of the 2N2907A to GND. The connection of the base to R593 is deleted. In
the closed position interdot blanking works, and works always, i.e.
independent of what happens at A16 and B7. When P600 is open the situation is
the same as with the previous P600 version. This version explains why I see
the dot blanking in other traces so clearly. About 50% blank of between
samples period is completely blanked.


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