I am troubleshooting a 465Bs which suddenly lost the channel 2 display trace.
I have the appropriate Tek service manual and test equipment including another working 465B.
My current troubleshooting approach is to trace the signal through the Ch 2 signal path and compare the signal levels to those in the correctly operating Ch 1 path. I¡¯ll describe the symptom details hoping that they will provide clues that someone will recognize and hopefully give me some guidance to help fix the fault.
I have measured all the power supply rails and verified that all are within the proper voltage and ripple specs.
While applying a 1kHz, 500mV sine wave signal to both channels, the detailed symptoms are:
? With both channels selected, only the Ch1 signal is visible on the CRT screen.
? Moving the Ch 2 vertical position control through its full range does not show any Ch 2 display.
? The Ch2 vertical position control affects the Ch1 trace as follows:
Beginning from the full CCW position the Ch2 position control has no effect upon the Ch1 displayed trace during the first 50% of rotation but proceeding CW through the last 50% of CW rotation causes the Ch1 displayed trace to move up 2.5 divisions.
? Using beam finder shows a trace for each channel. The Ch2 signal is shown as a flat line above the Ch1 sine wave. In this mode the Ch2 vertical position control does not move the position of the Ch2 trace as it does on my working 465B.
? When I switch the trigger source to Ch2 the displayed Ch1 signal free runs and no position of the trigger level control will re-establish a trigger lock. My thinking here is that the Ch2 signal is not making it through to the Ch2 trigger signal pickoff point. Therefore, the fault seems to be in the Ch2 vertical pre-amp circuitry and not within the vertical switching logic.
I¡¯m currently reviewing the manual for further clues but would certainly appreciate any helpful input from the TekScopes forum members.
Cheers,
Tom
Tom Phillips