More HP8640B info! - UK Vintage Radio Repair and Restoration Discussion Forum

LA9CHA Thorvald · 19th Jan 2021, 12:24 pm

A bit more, checked the square wave signal going into the filter unit. This was ok, but there is no output signal. From the circuit diagram "Divider filter assy 10840-60105 (A10A2) I see that the signal has to pass the relay K1-2-3-4 contacts. The +/- 5,2V is ok, and the relays are operated via "op.amp" U6A and B. Either one is on and the other is off. These are again controlled via transistor Q1 that creates a inversion of the signal from U1. So, if the U1 is defective, neither relays will be operated (correct?). the input signal to U1 changes level from 0,00V to 0,5V when changing bands. Any comments arte welcome!

19th Jan 2021, 12:24 pm	#1
LA9CHA Thorvald Tetrode Join Date: Dec 2019 Location: Egersund, Norway Posts: 85	More HP8640B info! A bit more, checked the square wave signal going into the filter unit. This was ok, but there is no output signal. From the circuit diagram "Divider filter assy 10840-60105 (A10A2) I see that the signal has to pass the relay K1-2-3-4 contacts. The +/- 5,2V is ok, and the relays are operated via "op.amp" U6A and B. Either one is on and the other is off. These are again controlled via transistor Q1 that creates a inversion of the signal from U1. So, if the U1 is defective, neither relays will be operated (correct?). the input signal to U1 changes level from 0,00V to 0,5V when changing bands. Any comments arte welcome!