Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal


Hello Roger,

I am back with some measurements.

** Vertical Switching **
Both measurements taken in ALT mode, no probe attached, and lowest TIME/DIV setting.

TP364 (-2V and -0.102V)
TP374 (-2V and -0.071V)

** Trig View **
With calibrator signal feeding Trig In, Trig Source set to Ext

Trigger Level Centered: when the beam is at the centre of the screen, the beam width is just under 1x sub-division
Trigger Level +++: when the beam is at the highest pos, that is +2.5 divisions above centre, the beam is just over 2 sub-divisions in width
Trigger Level ---: when the beam is at the lowest pos, that is -1.0 divisions below centre, the beam is also just over 2 sub-divisions in width

When at the center, there is a fuzzy glimpse of the square signal. However, when on +++ or --- positions then beam becomes entirely flat.

** Q322 and Q324 **
Using tester got the following values:

Q322: NPN, Gain: 75, Vf: 707mV
Q323: NPN, Gain: 71, Vf: 701mV

I should say I got (I think) bad news. I started hearing concerning cracking sounds for the first time while I was running the sweep at its slowest speed. At first, I heard like 5-7 in rapid succession. I powered off the scope and waited a little while. The scope cover was removed at the time, so I didn't get too close to the circuitry just in case. These sounds weren't too friendly. I increased the sweep speed before I turned it back on. Unfortunately, the crackling sound still persist - it doesn't seem to be related to the speed at all. In fact, it seems to be coming from the front of the cathode ray tube, but I can't be certain.

I made a short video where I captured 2 or 3 of the crackling sounds. My phone was capping out the percussive effect somewhat; the real sound is higher in pitch and volume.

Is this a concern?

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