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Old 10th Sep 2023, 5:29 pm   #1
high_vacuum_house
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Default Tektronix 545A main timebase switch access

Good afternoon,
I am trying to restore one of these beasts and have a fair bit now working.

There are some paper tubular capacitors on the A timebase switch which have failed. These are in the holdoff circuit in the timebase and prevent the timebase from running. I have managed to replace one so far which has got a few of the ranges working, though I cannot see any way of access to the remainder. The timebase switch is right in the centre of the instrument. I am stuck at how to proceed at the moment without a very severe dismantling of the instrument which I don’t really want to do.
Has anyone restored one of these in the past and has an idea on accessing the capacitors.

Many thanks,
Christopher Capener
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Old 11th Sep 2023, 5:55 pm   #2
6AL5W-Martin
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Default Re: Tektronix 545A main timebase switch access

hello from germany.
That`s a thing of interesting.
I have also one waiting for the repair table, I will get it and watch how to do this.

About the proper radios: YES. We have the same way in collecting.

greetings
Martin
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Old 11th Sep 2023, 6:55 pm   #3
Chris55000
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Default Re: Tektronix 545A main timebase switch access

It isn't particularly easy to get at the Timebase Speed Switch Assembly, but I think there is just barely room to withdraw it from behind the front panel once you've removed the knobs!

Tektronix used to supply this switch as a pre–wired part, with the special three section timing capacitor block unit, (C160G, C160H and C160J) so it should be separately removable!

I believe the multiple capacitor block has a reputation for internal failure, so you might have to be prepared to substitute sections of this!

Unfortunately none of the '545A pdf manuals online appear to have an exploded view or mechanical parts list in them from what I can see!

It might be worth looking in "Service Scope" from the first issue – there might have been dismantling hints in this journal – they're all available for free download from Tekwiki!

Chris Williams
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Last edited by Chris55000; 11th Sep 2023 at 7:04 pm.
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Old 11th Sep 2023, 7:07 pm   #4
6AL5W-Martin
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Default Re: Tektronix 545A main timebase switch access

for the multiple C from right side.

For the others, I would remove the CRT to get it from left side.
Chris know that, the set of capacitors at the switch is well selected, about that they sold oly complete sets.

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Old 11th Sep 2023, 9:27 pm   #5
6AL5W-Martin
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Default Re: Tektronix 545A main timebase switch access

when yozu remove the plugin, empty slot,
you can easy remove the side shielding plate, only 2 screws and 2 what are fixing cables, then the way is free to the switch.
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Old 11th Sep 2023, 11:38 pm   #6
high_vacuum_house
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Default Re: Tektronix 545A main timebase switch access

Good evening,
Many thanks for the tip, I will have go at removing the plug in side shield to get access to the holdoff capacitors. I think the special 3 capacitors in a tin unit is ok as I have tested these individually and are all roughly in spec.
I will look at loosening the switch unit in situ to see if I can rotate it to gain better access. I had to order a 1/16” Allen key to be able remove the knobs which hasn’t arrived yet.

Christopher Capener
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Old 12th Sep 2023, 7:49 am   #7
Craig Sawyers
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Default Re: Tektronix 545A main timebase switch access

I bought a complete set of imperial and metric keys from Screwfix https://www.screwfix.com/p/magnusson...0-pieces/3305v

It is the best fifteen quid I have ever spent!

Craig
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Old 12th Sep 2023, 2:11 pm   #8
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Default Re: Tektronix 545A main timebase switch access

Whilst your waiting for the Allen key, give the grub screws a soak in penetrating oil Chris. After 60 odd years of being stored in less than perfect conditions a lot of times they are seized solid. Diesel or heating oil works if you have nothing else. The worse ones are the little variable timebase or variable Y axis ones with little 3/16" ( I think) shafts, these can be a nightmare so get loose.

If you crack a knob I should have a spare.

Andy.
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