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I have a problem with horizontal display showing double or distorted image . It happens on both channels and I uploaded a photo in the album named :

485 Problem

If anyone has seen something similar or has any suggestion, any advice would be appreciated.

Thank you

Looks like a noisy contact in the X signal path.
Is the pattern stable or intermittent?
How fast was the sweep speed you used when you took the photo?
Does it react if you fiddle with the timebase selector, or the associated X controls?
Does it react if you gently tap the PCB around the X timebase/amplifier?

Especially looking at the start of the trace, it could simply be a matter of CRT bias adjustment. Simple to do and undo visually and no loss of calibration.

Raymond

Reply to Nenad:

The pattern is random, jumps around.
The sine wave was at 1 kHz so I tried a few different time base settings ( don't remember which ones ) but it was showing in all of them I tried.
I don't believe it's a bad contact at the time base switch since I tried wiggling it and sort of holding it a bit left and right and wouldn't do anything.
Haven't opened it yet so I couldn't try anything like taping.

Additional info: it shows right away when turned on, and warming up will not change anything in either better or worse.

Reply to Raymond

Haven't opened it yet. But I guess I'll have to try it one of these days.

On Wed, Jan 29, 2025 at 06:08 PM, Goran Parezanovic wrote:

The pattern is random, jumps around.

That's not something I would associate with the CRT Bias setting. In your image, retrace blanking seemed to be incomplete. Trying to adjust CRT Bias won't harm though...

Raymond

Check blanking and Z axis.

J

Thanks. I started with checking DC voltages of power supply and ( surprise, surprise ) there is a capacitor issue in the +140 V circuit. So there is a big ripple there.
First will have to fix this , and who knows, maybe this causes the display problem,

Goran,

It is best to totally recap this. I used Nichicon ULD, UCY and UHE for the secondary side and 470mfd LGR for the two screw mount cans off the mains. Raising the capacitance is fine. I did in mine. Also use a 25V for the replacement of a 15V tantalum on the 13V supply! This original will short causing a tic tic....

Replace R1651 and R1659 with Vishay VR37 types. These will be high causing the trace to be bright at first then dimming over 15-20 minutes without touching the intensity control. I did raise wattage of some resistors in mine in areas.

If yours is a 'lower' serial number, make the mod in the front ends for both channels to protect the ICs from damage when switching from 50 to 1meg. I did use a 16V cap for the 9V supply in the front ends.

Mark

Gentlemen, to all of you who got involved, thank you for responses and an apology, I just realized that due to the brain fog and the fact that I do have a few Tektronix oscilloscopes, this is happening on the 464 model !
The whole title of the thread is wrong - should be reading Tektronix 464.
I put the wrong model in the description !