Re: Tektronix 465
On 7/12/2019 8:25 PM, Abc Xyz wrote:
Wow...you really seem to know your 465B's Horizontal Circuit! Some ofOK, I don't have one, but there's a certain way most of them are designed. Firstly, go look at the block diagram of the vertical section.
Working from the plates backward, you have the output drivers. The deflection plates are designed so that with the same voltage on them, the beam ought to be pretty much in the middle of the tube, H, V or both as it may be. Shorting them together (temporarily, do with power off! then turn power on) makes both voltages equal and the beam ought to be in the middle. If it's not close, then something around the CRT is off.
Now looking at the output stage. Regardless of the voltage on the plates, if they're both the same, the beam ought to be centered.
If you can't get the beam centered, then likely check the output voltages from the vertical stages. Now, both plates ought to go *up* by the same amount, and *down* by the same amount. for instance (and these numbers are only for illustration), if the plates normally sit at 50 volts with the beam centered, then say that for the beam to be full left, one plate is at 30 volts and the other is at 70 volts (+/- 20). The exact same thing is true if the beam is at the other side, except that the one that was at, say, 70, is now at 30, and the one that was 30 is now at 70.
If one output amplifier can only do 10 volts swing, or say, stops at 50, then the difference between the plates (important!) is half of what it needs to be, but only on half the screen. 70, 30 becomes (instead of 30, 70) 50,70.
That could be the whole problem. (and likely is).
Now the question is, why?
grounding the input of the amplifier *ought* to give you no deflection, so the only way that the trace moves is by the position control.
what you need to do is to use the position control to move the spot (low intensity please!) left and right
go through each stage and record the voltage swings at the output of each amplifier stage
they ought to be the same, or very close
what I might suspect is that the output amplifiers, which might be a totem pole (one pulls up, one pulls down) and one for each plate, well, one of them is messing up, so I'd just suspect the output transistors to start with.
I can tell you that the Left Deflection Plate Voltage is +47.9V Measured