Tektronix 434 s/n below 500000 faulty ps.

[johnmcgivern]

The cal spindle was just spinning I tightened the grub screw but it made no difference it clicks into cal fully clockwise and also fully anti clockwise.
I measured resistance of pot at the end of the spindle while turning the knob resistance remained at about 2kohms pot must be seized at this position.

[Craig]

If I turn the Timebase cal knob fully clockwise or anti clockwise nothing happens to the waveform. The pot does nothing.

Which Timebase cal knob is this?

Craig I am really sorry for asking all these questions I have watched many oscilloscope videos and tutorials but its like learning to drive you can read and listen but nothing beats practicle experience and making mistakes which I am trying my best to avoid with this scope due to rarity of parts.
See photo's when timebase set to 0.1m/S should each gradient have a signal?

You are pointing to the Variable Time/div knob. This has nothing to do with triggering

The shaft that connects the knob to the variable control (R799 diagram 8) has the knob screwed on at one end with a grub screw (which you have already tightened), and at the other end is secured to the control with another screw. That screw might be loose, so the knob and shaft rotates but the shaft just spins uselessly in R799. See if you can find the screw on that control and tighten it.

Craig

[Craig]

The cal spindle was just spinning I tightened the grub screw but it made no difference it clicks into cal fully clockwise and also fully anti clockwise.
I measured resistance of pot at the end of the spindle while turning the knob resistance remained at about 2kohms pot must be seized at this position.

Is the end of the control moving?

[johnmcgivern]

Yes Craig the little nylon cross piece with the grub screw turns with the cal knob but the two wires connected to the pot at the end of the spindle read approx 2kohm which leads me to assume the pot is seized.
This has 2 screws securing it to the end housing bit wary about removing it as it looks like a sealed pot.

[johnmcgivern]

The pot: item 108 page, 183 exploded diagram , unfortunately the mto just says variable resistor.

[johnmcgivern]

Disconnected pot and removed spindle I will grind a flat on the spindle as it jams in cal position this should stop it spinning.
The actual Timebase is out of sync. The knob is solid in the proper position but somehow the settings have moved they seems to be about a factor of ten maybe more out. One single signal at 1 kHz covers 10 gradients on my other scope, on the Tek scope same signal is shown 4 times across 10 gradients instead of 1 signal.
Hope this makes sense.

[johnmcgivern]

Success gentlemen , I desoldered the var pot removed spindle filed flat on spindle.
Lubed pot and exercised refitted everything managed to get the correct frequency on display.
Could really do with a new pot but cannot source one had a look at qservice etc. No joy.
Many thanks everyone again cheers Craig be lost without you mate.

[Craig]

The pot:   item 108 page,    183 exploded diagram ,   unfortunately the mto just says variable resistor.

Don't look at the mechanical exploded diagram. Look at circuit diagram 8 on page 167. R799 is the Variable Time/div. 10k

Ah - just looked at your last post - superb!

[johnmcgivern]

Ok Craig thanks again for your expert help.

[johnmcgivern]

Frequency looking good now left on for a couple of hours next day decided to put all back together.
Turned on and crackle arc shooorrrted aaaaaarrrggghh.
Back to square one removed cover checked for arcing can't see anything obvious. Turned on no lights no low voltages at all just 240vac.
Think diode bridge shorted.
Can anyone suggest a replacement diode bridge.