Tektronix 464 - Horizontal Deflection Switch

[mldevw]

Hello,

I recently bought a Tektronix 464 Oscilloscope and I think it makes a rather good screen for my computer, as you can see in the image attached.

But there is one serious issue: The horizontal time deflection switch does not work properly in every position. Especially on the slow setting (high time per division that is) it only works when the knob is pushed to the right of the instrument.

Suspecting the switch contacts, i disassembled it, as depicted by an illustration of fellow member xtoffer below, and cleaned each contact with isopropanol. Still the issue persists though the switches visually seem to make contact.  Do you have an idea what I could check next or is this fault common to you?

Assembling the knob on the shaft was a kind of trial and error... do you have a hint how to do this properly?



Thank you in advance.

Cheers,

mldevw

[bd139]

Got a 475 here with same trouble I haven't got around to yet and have fixed a 465 with the trouble before.

This usually happens because either the bearings are worn on the shaft, the cam shaft is worn or the contacts are bent or the plastic ends worn. In this case as it's consistent with lowest speed settings, probably the cam shaft or plastic ends. You will have to hook up a continuity tester in situ (before removing it!) and work out which contacts are problematic. This should be done with the assembly fully assembled. Then you will need to very carefully inspec the switch and possibly bend the offending switch hinge up at the soldered end and then down again at the other end without breaking them. This will give more positive cam push on the switch and should resolve the issue. Also look for broken fingers on the switches.

If fingers are broken or damaged the timebase is a write off and you'll need a donor one.

Close up from a 465 I did here:

[mldevw]

Hi,

thank you for your input. Iwill try to fix it this weekend and give subsequent report.

Cheers,

mldevw

[mldevw]

Hi again,

thanks to bd139 for giving me the hint on rebending  the contact spings. As my camshaft seems to have a bit of wear I decided that I have to bend them two ways (up in the back near their attachment and down at the finger side) to give them just a little bit more travel.

Now everything works again nicely, even surfing on eevblog 


Cheers

mldevw

[bd139]

Glad to hear it works again 

You have motivated me to fix my 475A now