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Old 8th Feb 2017, 3:52 pm   #1
HowMuch!
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Default Another Tek 465 Problem

Hi everyone. Advice please.

I was on this forum 3 or so years ago with a problem on my Tektronix 465 Oscilloscope, which with your help I was able to solve. Guess what...I thought I had the same problem again, but this time I'm pretty sure it's more serious.
The internal 1.5amp fuse on the 15v unregulated supply has blown, and a bit of probing seems to show transformer T1420, (the high voltage transformer?that supplies the CRT heater, and the high voltage for the same, has a short to earth on the primary. It isn't short circuit tantalums, that was the problem last time and they have been replaced, and checked ok again.
Can I source this part anywhere? Can it be rewound. Should I put the scope on Ebay as 'for parts/not working'.

The scope itself is in pretty fair condition, I've owned it for 10 years or more, and I would like to keep it going if I can.
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Old 8th Feb 2017, 6:36 pm   #2
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Default Re: Another Tek 465 Problem

If C1419 is ok, have you checked Q1418 for a collector emitter short?

Roger
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Old 8th Feb 2017, 9:46 pm   #3
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Default Re: Another Tek 465 Problem

Hi Roger. It would appear that after 40-something years in the trade I still can't use a multimeter. It is C1419 tantalum that is short circuit after all, I don't know what I did, because I'm certain I lifted one leg of the capacitor and the short was still there. However, on testing again I see that the cap is a dead short, and on replacing it with an electrolytic the scope powers up ok. Maybe I won't order that Rigol tomorrow after all.

However I have read that these transformers now run hot and are prone to fail as the potting compound breaks down with age. My 15 volt unregulated is actually nearly 24 volts. Should I try to reduce this, will that help with overheating? There are other niggles with the scope that I'm going to try to fix too.
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Old 8th Feb 2017, 11:10 pm   #4
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Default Re: Another Tek 465 Problem

The manual shows 15v unreg as well over 20volts so I think that is quite normal. I know transformers do fail with age but every time I come near to convincing myself that a transformer has failed it turns out to be a capacitor or semiconductor!

I actually enjoy fixing old test equipment but it does mean I have to always have at least one working scope.

Roget
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Old 8th Feb 2017, 11:14 pm   #5
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Default Re: Another Tek 465 Problem

Plus a third as a parts mule. That was my Tek 465 ownership experience
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Old 9th Feb 2017, 12:30 am   #6
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Default Re: Another Tek 465 Problem

Quote:
Originally Posted by HowMuch! View Post
However I have read that these transformers now run hot and are prone to fail as the potting compound breaks down with age
There was a shortish period of about 4 years where Tek used epoxy potting that ended in about 1970. The later model 500 series (like the 545B) and early 576 curve tracer used this. And yes, they suffer from the epoxy breaking down and the winding losses escalating. The symptom is that the trace dims and loses focus, or the voltage regulators crowbar.

But post 1971 latest they rumbled that there was a problem an moved across to silicone impregnation, and that cured the problem.

There were remaining problems, particularly with the 7834 storage scope in particular with shorted turns. And that transformer is a real nightmare to rewind, although some intrepid Tek fans have succeeded in rewinding it.

But I have not heard of any of these sort of problems with the 465/475/485 series.

Craig
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Old 15th Feb 2017, 5:26 pm   #7
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Default Re: Another Tek 465 Problem

Hi again. That's good news about the transformer, thanks for that information Craig. As I mentioned, this scope has some other problems I'd like to fix. Should I start a new thread?
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Old 16th Feb 2017, 1:20 am   #8
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Quote:
Originally Posted by Craig Sawyers View Post
However I have read that these transformers now run hot and are prone to fail because the potting compound breaks down with age.
Quote:
Originally Posted by HowMuch! View Post
But I have not heard of any of these sort of problems with the 465/475/485 series.
I've had two 475 'scopes which I owned and one 485 in a previous employment that I then used regularly, all of which failed that way. For all three, replacement parts were not obtainable, so they were scrapped.

Al.
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Old 17th Feb 2017, 2:02 pm   #9
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Default Re: Another Tek 465 Problem

As no one has told me to start a new thread I'll carry on here.
That's bad news about the transformer, but as it's working I'll worry about that when I need to. Right now I want to remove the 'Trigger gen & sweep logic board' It's the board that carries the Coupling and Source slide switches (not sure that's really the right name for them). Has anyone had experience of this? Does it come out as one assembly including the slide switch levers? Here is a photo of the board in the scope.
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Old 17th Feb 2017, 2:32 pm   #10
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Default Re: Another Tek 465 Problem

If it's the lever switches, they come out with the board on the 465B at least. It's pretty difficult to get most of the boards out of a 465 from experience; it's like that scene in The Matrix where he wakes up in the pod in the real world.
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Old 17th Feb 2017, 3:39 pm   #11
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Default Re: Another Tek 465 Problem

Quote:
Originally Posted by HowMuch! View Post
I was on this forum 3 or so years ago with a problem on my Tektronix 465 Oscilloscope...
https://www.vintage-radio.net/forum/...d.php?t=105996
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Old 28th Feb 2017, 6:31 pm   #12
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Default Re: Another Tek 465 Problem

Another question. Does anyone know what size Allen Keys I need to remove the control knobs? I thought 1/16 was the size I needed and ordered a set with that size, but no, the key is slightly too small and turns in the head. The next size up, 5/64 is way too big. The grub screws themselves look in good condition and not rounded. Have CPC supplied a set with a duff key? I don't have anything to measure the key right now. http://cpc.farnell.com/duratool/d005...ial/dp/TL11386
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Old 28th Feb 2017, 6:39 pm   #13
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Default Re: Another Tek 465 Problem

Tek ones are usually 5/64 or 50 thou (0.050").

TBH I use a Wera Torx driver from the following set - one of them fits like a glove and doesn't shred the grub screws like cheap allen keys do but I reckon this is probably frowned upon

https://www.amazon.co.uk/dp/B009ODV0PI


Also check RS for allen keys. You can get 5 of any size for about 1.58 + VAT including next day courier delivery
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Old 28th Feb 2017, 6:40 pm   #14
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Default Re: Another Tek 465 Problem

I am sure many will frown on this, but Torx drivers are slightly tapered and often will grip a slightly worn hex screw.

Roger

This crossed with the previous post!!

Last edited by RogerEvans; 28th Feb 2017 at 6:41 pm. Reason: crossed with previous post
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Old 28th Feb 2017, 6:42 pm   #15
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Default Re: Another Tek 465 Problem

Glad I'm not the only one that noticed that. I cringed slightly when I was typing it
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Old 28th Feb 2017, 6:47 pm   #16
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Default Re: Another Tek 465 Problem

Control knobs & their associated setscrews are listed on page 271 of the (30MB!) PDF file available on the eDebris Boat Amchor Manual Archive:

http://bama.edebris.com/download/tek/465(2)/465.pdf

The appropriate hexagonal keys can be obtained from Model Fixings:

http://www.modelfixings.co.uk/tools.htm#allen keys

Very helpful and very quick! (satisfied customer => HP8640B/Tek7xxx restorer)

Hope this helps.

Cheers

Guy
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Last edited by Nymrod121; 28th Feb 2017 at 6:52 pm. Reason: another restoration category
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Old 28th Feb 2017, 7:42 pm   #17
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Default Re: Another Tek 465 Problem

Many thanks for your fast replies. I don't have any tiny Torx on hand at the moment. Having just moved house most of my tools/junk are spread between storage and relatives too polite to refuse it. I'll try to measure the Allen key to confirm that a wrong size hasn't somehow been supplied. Thanks for the link to the manual. The screw sizes are listed but not the appropriate key to fit? Maybe I'll work it out after a longer look. I'll get them out somehow.
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Old 28th Feb 2017, 8:48 pm   #18
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Default Re: Another Tek 465 Problem

1/16" is about 1.6mm. A 1.5mm allen key is a standard metric size but will slip like mad in a 1/16" screw. You haven't been using that one by mistake. I've seen, alas, many cheaper sets of allen keys, drill bits, etc that are mis-marked like that.

Although I still want to know why Xcellite sell a 0.05" hex tool and a 1.27mm hex tool under different part numbers.

Another one to watch for are Bristol Spline screws. Some manufacturers used them as grub screws in knobs (I have a Trend telegraph test signal generator with one in the multiturn knob for the output voltage). No allen key or torx driver will fit that. I don't think Tektronix used them, but ..
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Old 28th Feb 2017, 8:57 pm   #19
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Default Re: Another Tek 465 Problem

I recall 'Bristol Spline' fixings appearing in the Hewlett Packard 8640B parts lists ... cue Radio Wrangler ... ?

Guy
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Old 28th Feb 2017, 9:14 pm   #20
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Default Re: Another Tek 465 Problem

Quote:
Originally Posted by Skywave View Post
I've had two 475 'scopes which I owned and one 485 in a previous employment that I then used regularly, all of which failed that way. For all three, replacement parts were not obtainable, so they were scrapped.
Al.
I've been a very active member since 2002 of the yahoo group Tekscopes (around 8000 members) and I cannot recall anyone reporting any HT transformer problems with that series of scopes, but I'll ask the question just in case my mind is playing tricks.

A common failure mode with many Tek scopes is with the voltage multiplier.

Craig
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