Re: Tektronix 465

Harvey White

On 7/12/2019 8:25 PM, Abc Xyz wrote: really seem to know your 465B's Horizontal Circuit! Some of
what you Suggest I Understand... some of it I Do Not. LoL
OK, 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
(+52.0V Schematic) and the Right Deflection Plate Voltage is +41.4V
Measured (+52.0V Schematic).


On Jul 12, 2019 5:09 PM, "Harvey White" <madyn@...> wrote:

Then I guess we need to do it the hard way.

Looking at the horizontal plates, short them together temporarily.
Whatever you get ought to be centered horizontally (more or less) and
vertical we don't know about.

That tends to verify the CRT.

Secondly: center the horizontal positioning. Use a spot (DC H input)
with the intensity down so you don't damage the screen. Put the
centering control to mid position.

Check the voltage excursion from full left to full right, and then check
the voltage when centered. The difference between the plates when full left

and full right should be rather close.

If one output (for instance, the one for the right plate) is limited in
range, then your problem is in that half.

For this test, I'd turn the intensity down completely. Center the
centering control, do X input, and make it a zero. If everything is
correct, then the spot ought to be centered once you turn the intensity up.

look for balance between the channels as you go from the input to the

If you have a properly centered spot, and still the trace can't go far
right, then the fault is that the right plate driver doesn't have enough
voltage excursion. The fault is likely after the centering pot. (note:
check the voltages to the stage before the centering pot, it ought to be
the same on both + and - drivers.

If you can't get a properly centered spot with the centering control,
then that suggests that the circuitry before the centering control is
out of balance.

With the input grounded (a good idea), somewhere, someplace, something
is out of balance if the problem is that the spot is not centered. If
on the other hand, up to the centering control everything is balanced,
then past that, something is either not balanced, or something doesn't
have enough of an excursion (running output voltage range) to make the
circuit work.


On 7/12/2019 4:07 PM, Raymond Domp Frank wrote:
On Fri, Jul 12, 2019 at 10:00 PM, Abc Xyz wrote:

Even Textronix, and others, said there was no IC in
the Horizontal Section.
You're right, that 5-transistor array *is* an IC.


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