Author Topic: Tektronix 465 Repair and Restoration  (Read 30978 times)

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Offline ModemHead

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Tektronix 465 Repair and Restoration
« on: January 24, 2012, 01:25:16 AM »
After buying and refurbishing some older Fluke DMMs for use on my workbench during the past couple years, I recently decided to try something a little more complicated. So I found a crusty old "parts or repair" Tektronix 465 on eBay. It looked physically intact and the pix showed that it at least made a dot when the beam-finder button was pushed. Good enough, so I set about to win the auction.

The scope arrived safe and sound since it was well-packed. And yep, it was a bit dirty and pretty much dead. Looks as if it has spent the last 20 yrs in someone's garage.



Looking inside: The sweep/trigger board, with the timebase board behind it. Power supply transformer and filter caps are visible towards the rear.



The vertical amp board is on the other side.



The power supply, high-voltage, horizontal deflection and calibrator circuit are on the bottom board:



The vertical deflection driver is nestled in beside the CRT neck.  Lots of flying leads and point-to-point construction on the output. I won't be touching this unless absolutely necessary.



Powering it on, I got a dot when I pressed the beam-finder, and that was it. Checked all the power supplies, all of them are pretty much spot-on with no ripple to speak of. All of the transistors are socketed, so since there were some signs of oxidation, I re-seated every transistor I could get my fingers on. Horizontal sweep appears! Looks linear and perfectly normal. But no vertical deflection at all, including the position controls. And the intensity control has to be turned all the way up to see anything. Which leads to the trace disappearing at higher sweep speeds.

The Tek 465 has a "trigger view" switch which basically disconnects both vertical amps and instead connects the vertical deflection driver to a trigger signal sample from the sweep/trigger board. It's a cam and leaf arrangement built right onto the PC board. Punching this switch vigorously showed some noisy vertical deflection. Examining the switch I can see some crud in it.



So I cleaned it by soaking a paper strip in IPA and moving it back and forth between the contacts.



Vertical deflection now looks pretty good, so on to the intensity problem. Selecting either the "Mix" or "A-intensified" horizontal modes should result in the delayed section of the sweep being very bright. Instead, it seems this section is about the only thing readily visible. The regular part of the trace is just barely visible with the intensity turned to max. Not normal, but somewhat promising.

The high voltage supply is supposed to be -2450V. Checking it shows -2400V, so I tweaked the HV adjustment up a bit. The manual says the CRT grid bias should be adjusted for a dim dot in X-Y mode when the intensity control is set for a 20V output on the Z-axis (intensity) amp. Interesting, the Z-axis amp output will only go to 15V with the control at max. The Z-axis amp consists of 4 discrete transistors, so I check through it and can't find anything wrong. The inputs to this amp are several diode-ORed signals from various places.  Blanking inputs pull up, intensifying inputs pull down. So I start checking the blanking inputs, and when I get to the "Chopped Blanking" input, it looks fishy. Pulling the cable for this input results in a very bright trace!

Working backwards, the chopped blanking signal comes from a common-emitter transistor amp, which is fed from a small toroidal coupling transformer. It's supposed to provide beam blanking while the beam traverses from one channel to the other in chop mode. The transistor tests good, but is never turning on because it appears to have no DC bias. This results in the collector resistor pulling up the Z-axis input really hard. Found it! The secondary winding on the toroid is broken right in the middle. It appears to have taken a serious blow, perhaps from the case of the scope.



As a temporary fix, I scraped some enamel off of each broken end and made a little solder splice. I'll make a more permanent repair after locating some enameled wire to rewind the secondary.



Success... It's alive!



And happy.



Further checkout reveals no other major problem that I can find. Both vertical and horizontal calibration is a little off, but not too much. The front panel area needs serious cleaning, and of course all the vertical attenuator and timebase switch contacts as well. I'm pleased and somewhat surprised that the scope is operating this well without having to replace a single component (except for the bypass cap I broke with a pair of needle-nose pliers.)



Next up, some disassembly and cleaning...

Offline Teknotronix

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Re: Tektronix 465 Repair and Restoration
« Reply #1 on: January 24, 2012, 01:40:32 AM »
Nice! It's great seeing some of these old scopes being cleaned up like new.
Don't drone me bro!


Offline ModemHead

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Re: Tektronix 465 Repair and Restoration
« Reply #2 on: January 24, 2012, 02:04:52 AM »
Yea, I find the work quite satisfying. Speaking of being cleaned up...

The front panel is grimy and the structural plate of aluminum behind it is suffering from oxidation/corrosion, especially around the holes. This scope has not seen a humidity-controlled environment in years...



After removing the sweep/trigger board, the timebase board is accessible.  This is the A and B timebase range control with the cover off. More delicate cam-and-leaf stuff to clean. I used more paper strips and IPA, then finished up with some Caig De-oxit for good measure.



The front panel was cleaned with IPA, then scrubbed with a toothbrush and baking soda toothpaste.  All the knobs and plastic bits got the same treatment.



More cleaning and dusting, resulting in a pile of scope bits to re-assemble.



Re-assembly started. Vertical amps and sweep/trigger boards re-installed. The front aluminum piece was cleaned with a Dremel tool with an emery wheel. No more corrosion.



Getting the pots, controls and front-panel bits back in order. The BNC jacks were cleaned with a Dremel tool with a wire brush attachment. At least on the outside, not sure how to get the inside part.



The old power cord was stiff, cracked and nasty-looking, so a new one has been re-installed. The old strain relief was cleaned and re-installed along with the new cord.



Re-assembly complete and ready to re-test.



The trigger-view switch acted up again. I cleaned it once more with IPA and also treated with some Caig De-oxit. It has behaved properly since then.



Nice sharp traces for an old scope.



The service manual has an extensive procedure for performance checks and calibration, so the next big thing is to go through that.  For now though, I think I'll just work on improving the appearance of the outer shell.  Does spray paint come in Tektronix blue? :)

Offline tekfan

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Re: Tektronix 465 Repair and Restoration
« Reply #3 on: January 24, 2012, 02:13:47 AM »
Great work repairing this lovely scope. Just goes to show how reliable old components really are. Looks like this one is from the mid 70's or thereabout. Those big silicone coated non inductive resistors in the vertical amplifier always looked very strange to me.
I always find that cleaning the buttons and knobs is the most annoying task.
One can never have enough oscilloscopes.

Offline ModemHead

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Re: Tektronix 465 Repair and Restoration
« Reply #4 on: January 24, 2012, 02:24:31 AM »
Thanks.  Those ceramic capacitors that look like wirewound resistors are strange to me. Of course, when this scope was made I was barely a teenager, whose favorite store was Radio Shack.

The most annoying task to me was cleaning all those switch contacts. I kept worrying that one wrong move and the game was over, if one of those little leafs got bent.

Offline w2aew

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Re: Tektronix 465 Repair and Restoration
« Reply #5 on: January 24, 2012, 08:36:12 AM »
Seriously nice job!
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YouTube channel: http://www.youtube.com/w2aew

Offline Richard W.

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Re: Tektronix 465 Repair and Restoration
« Reply #6 on: January 24, 2012, 08:54:31 AM »
Wow, it looks really good. I'm impressed. But what's the trick behind the smiley?  ;D
The scope doesn't seem to be in XY-mode at first sight...

Offline amspire

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Re: Tektronix 465 Repair and Restoration
« Reply #7 on: January 24, 2012, 09:11:00 AM »
Wow, it looks really good. I'm impressed. But what's the trick behind the smiley?  ;D
The scope doesn't seem to be in XY-mode at first sight...

This photo might give you a clue:


Offline ModemHead

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Re: Tektronix 465 Repair and Restoration
« Reply #8 on: January 24, 2012, 09:25:25 AM »
Wow, it looks really good. I'm impressed. But what's the trick behind the smiley?  ;D
The scope doesn't seem to be in XY-mode at first sight...

An even better clue: Set the B-sweep up to catch just the right parts of a square wave on CH 1 and a sine wave on CH 2, then display the A-sweep, with the B-sweep portion intensified. Turn the intensity way down so only the intensified portion is visible, and you have the "Happy Tek" version of the old "Happy Mac" self-test icon.

Offline lowimpedance

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Re: Tektronix 465 Repair and Restoration
« Reply #9 on: January 24, 2012, 11:45:37 AM »
 What a little beauty  :) , started my electronics life with the 465b as the main 'weapon of choice' so have a soft spot for it.
 I also like the modded fluke 8050 in the background. (noted from the other thread, which I have kept a copy of, will be quite useful when my 8050 lcd packs it in!).
I'm sure you had just as big a smile as the 465!!.

John
You call that current ?.......
I'll show you current !

the odd multimeter or 2 or 3 or 4...or........never mind

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Re: Tektronix 465 Repair and Restoration
« Reply #10 on: January 24, 2012, 08:24:17 PM »
Good work! I would be hesitant to take a wire brush to a BNC connector, since you'll strip of the plating. This is especially bad for silver plated connectors, since silver oxide is conductive, so you're unlikely to see any improvement.

Offline krivx

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Re: Tektronix 465 Repair and Restoration
« Reply #11 on: January 24, 2012, 11:20:32 PM »
Good work! I would be hesitant to take a wire brush to a BNC connector, since you'll strip of the plating. This is especially bad for silver plated connectors, since silver oxide is conductive, so you're unlikely to see any improvement.

Is there a better way, apart from just replacing the connector? I have a scope with pretty dark BNC connectors, I just sprayed them with contact cleaner and wiped away any loose crap. It works, but I'd be happier with cleaner connectors.

Offline ModemHead

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Re: Tektronix 465 Repair and Restoration
« Reply #12 on: January 25, 2012, 12:29:15 AM »

Good work! I would be hesitant to take a wire brush to a BNC connector, since you'll strip of the plating. This is especially bad for silver plated connectors, since silver oxide is conductive, so you're unlikely to see any improvement.

That's a valid concern. Although a Dremel wire brush is not nearly as abrasive as one might think. The readout actuator rings were intermittent before cleaning, they work well now.

Is there a better way, apart from just replacing the connector? I have a scope with pretty dark BNC connectors, I just sprayed them with contact cleaner and wiped away any loose crap. It works, but I'd be happier with cleaner connectors.

If it's really discolored, maybe one of those dry silverware polishing cloths might improve the appearance. Silver polish might work, but I'd be concerned about getting residue inside the connector.

Offline ModemHead

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Re: Tektronix 465 Repair and Restoration
« Reply #13 on: January 25, 2012, 12:36:49 AM »
What a little beauty  :) , started my electronics life with the 465b as the main 'weapon of choice' so have a soft spot for it.
 I also like the modded fluke 8050 in the background. (noted from the other thread, which I have kept a copy of, will be quite useful when my 8050 lcd packs it in!).
I'm sure you had just as big a smile as the 465!!.

John
Yep, I can understand the urge to be a scope collector.  Must... resist...

I have more detailed pix and information on the 8050A LED modification that I could post, if there's interest.

Offline Chris Wilson

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Re: Tektronix 465 Repair and Restoration
« Reply #14 on: January 25, 2012, 06:04:52 AM »
Wow, beautiful restoration, a credit to you.  I am the newbie with the poorly 475, as you are obviously intimate with these things may I ask you a question please? Driven off the spindle the Time / Division knob, inside the casing, is a microswitch, with a single round alloy ring with a peg sticking it of it. My microswitch moves little, if at all, whatever is done turning or pulling the Time / Division knob. I will get the meter on it later, and see if it actual changes state, I suspect not unless it's incredibly sensitively set. Can you briefly describe how the microswitch should be triggered, and what it does please? I have found other issues with mine that I will mention in the "Tek 475 is this likely to be a straightforward repair thread. That rebuild is lovely, I am very envious of your patience.
« Last Edit: January 25, 2012, 06:10:11 AM by Chris Wilson »
Best regards,

                 Chris Wilson.


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