I have yet another plugin where P-P AUTO isn't working as it should. With a six-division sine wave, I can adjust the LEVEL to the second positive division maybe to two and a half negative divisions. If I change the SLOPE to the other direction, those levels are reversed but in neither SLOPE can I cause triggering to start fully three positive divisions and three negative divisions.
The 7B80 uses a Tek Custom chip, 155-0126-00, for the "TRIGGER SOURCE SELECTOR AND P-P AUTO AMPLIFIER" and the pins for PEAK DETECTOR OUT show a - and + by those pins (14 is - and 15 is +). I presume that indicates the voltage changes expected on pin 14 is when the LEVEL control is on the "-" side (7:00 to 12:00 position) and the voltage changes on pin 15 is when the LEVEL control is on the "+" side (12:00 to 5:00). Is that correct? It at least agrees with what I'm seeing on those pins. If so, then perhaps the problem with insufficient adjustment range in P-P AUTO lies with the circuitry in/around U75 and/or U55. Is that a reasonable assumption?
I took a look at the design for 155-0126-00 and it answered a couple of questions I had but I get a bit lost in that schematic pretty easily.
Thanks,
Barry - N4BUQ
