Sony/Tektronix 326 scope trace disappears on some time/div settings

[Tim88]

I bought this neat little scope 7 years ago and shelved it. It was missing the detachable power pack/charger and miraculously, one popped up on the ebay for $9.99! Anyway, it works, kinda. On certain time/div settings, the trace either disappears or kinda fades in and out with the intensity. The kinda trace fades settings are 10ms, 1ms, .1ms 10μs, 2μs, 1μs and the trace disappear settings are 5ms, .5ms, 50μs, 5μs, 1μs. I discovered, quite on accident, that if you turn the cal knob out of its calibrated position (about half way), the trace comes in on the CRT. In the manual, there is a nice schematic of the timing board and the problem settings match up with switch positions exactly.

So, tested the switch, tested fine. Used an ohmmeter from point AH to points AA and Z (where I figgered the problem was) and it tests perfect, 0 ohms. Checked the timing resistors and the cal pots R622 and they are perfect. The -5 volt CC to the pot is dead on.

I am usually pretty good at figgering out problems but this has got me at a dead end. Thought sure it was that daggum switch, then that daggum pot. I need some fresh eyes, what am I overlooking?

[Tim88]

A couple more sch of the horizontal section.

[Jeff eelcr]

Age? check capacitors would be my first thought, not that I am familiar with that scope.
Jeff

[med6753]

I'm not familiar with that scope and while looking at pictures it appears that it does not have an "Auto" mode for the triggering. Is that true? If yes, there may not be an issue. If you apply a signal to channel 1 and select triggering to channel 1 and then rotate the triggering control does the trace appear and lock in the time setting where it was previously missing? If it does I would say that's normal function for that scope.