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My 2465B suffers from a miss-tracking of focus with intensity.
When the intensity is turned up (75 to 100%) I have to re-adjust focus. When I do this the readout is out of focus (because it is a lower intensity).

Is this a problem that can be corrected by the "High Drive Focus" adjustment or is it likely to be a component failure in the z-axis amplifier?

Check out power supply, CRT, HV cal procedure first.

Likely failing caps or HV resistors

Jon

On Thu, Jan 16, 2025 at 11:03 PM, vk2bea wrote:

My 2465B suffers from a miss-tracking of focus with intensity.
When the intensity is turned up (75 to 100%) I have to re-adjust focus. When I
do this the readout is out of focus (because it is a lower intensity).

Are you using your 'scope to light the room? Why else would you use such high intensity? None of my (40+) analog Tek 'scopes fully keeps focus at between 75 en 100% CW of Intensity. You say you have to readjust, so you can get it back into focus, not that the trace totally loses focus. That makes it unlikely that your CRT is fatigued (i.e. old, dying).

I guess more detail is needed.

Raymond

On Fri, Jan 17, 2025 at 04:23 PM, Raymond Domp Frank wrote:

Are you using your 'scope to light the room? Why else would you use such high
intensity? None of my (40+) analog Tek 'scopes fully keeps focus at between 75
en 100% CW of Intensity. You say you have to readjust, so you can get it back
into focus, not that the trace totally loses focus. That makes it unlikely
that your CRT is fatigued (i.e. old, dying).

I guess more detail is needed.

Re-reading your message: Are you saying that when you need to use a high Intensity setting to achieve reasonable trace brightness because of low trace duty cycle/fastest hor. speeds, readout loses some focus? That's another matter and adjustment of (high intensity) focus should be optimized.

Raymond

The 2465B should keep focus when you turn up the intensity (at least you shouldn't need to change focus from low intensity to high intensity).

Quote from the manual:
"Focus tracking for intensity (VZ OUT) level changes is provided by the VQ OUT (quadrapole output voltage) signal at pin 22 of U950. The VQ OUT signal varies the focusing voltages (and thus the focusing strength) of two quadrapole lenses in the crt (diagram 8). The VQ OUT signal is related to the VQ OUT level exponentially and provides the greatest auto-focus control at high intensity levels. Gain of the VQ OUT signal is set by the High-Drive Focus adjustment, R1842. "

I did the cal 08 procedure and the "High Drive Focus" was out quite a bit.
Now it keeps focus throughout the intensity range. The trim pot is now set close to the end of range so I suspect something on the A9 board has drifted.
(although the "High Drive Focus" trimmer is just housed on the high voltage (A9) board ... it just sets a voltage on a pin of U950 IC/hybrid on the main board (A1)).

All the voltages on the low voltage board are spot on. I'll check the high voltage board (after I borrow an HV probe!).


Michael

On Fri, Jan 17, 2025 at 10:56 PM, vk2bea wrote:

I did the cal 08 procedure and the "High Drive Focus" was out quite a bit.

Congratulations!

I meant High Drive Focus when I wrote (high intensity) focus.

Raymond

Michael,

Resistors: R1853, R1854, R1871, R1872 and R1880 are stressed. It is advised to make them 1W 1%. when these go bad, the focus will be off or not at all. R1991 is advised to replace with a 1% type. Mouser has these. For R1991, there is a radial blue body style that will have its leads drop in the holes. A 1/2W axial is available in Vishay VR37 series. The original 1/4W carbon will be way out of tolerance. R710 and R910 are likely out of tolerance. A pair of 20 meg resistors in series will work as replacements for each resistor.

Mark

On Fri, Jan 17, 2025 at 03:41 PM, Mark Vincent wrote:

Great information .. just the guidance I was looking for. Thanks, I'll make the changes!

Resistors: R1853, R1854, R1871, R1872 and R1880 are stressed. It is advised to
make them 1W 1%. when these go bad, the focus will be off or not at all. R1991
is advised to replace with a 1% type. Mouser has these. For R1991, there is a
radial blue body style that will have its leads drop in the holes. A 1/2W
axial is available in Vishay VR37 series. The original 1/4W carbon will be way
out of tolerance. R710 and R910 are likely out of tolerance. A pair of 20 meg
resistors in series will work as replacements for each resistor.

Michael,


Make sure to tick the 'in stock' box. These are the radial types. The lead spacing of the leads will match the original 100meg resistor. I do not remember the exact hole spacing.

Mark