Restore Tektronix 465M oscilloscope.

[Kevwr]

I just purchased my first Tektronix scope, well 2 actually but only 1 shows a trace. My hobby is the restoration of valve radios but I thought it would be nice to restore what I think is a very cool oscilloscope.

Would I be right in saying that you start with checking the power supply circuits?

With radios I tend to change out the electrolytics as a matter of course, is that necessary on these scopes. I’m thinking this hasn’t seen power for 20 years judging by the Ministry of Defence label showin calibration due year 2000.

I have briefly applied power and saw a nice trace before promptly turning it off.

[agent_power]

Yes, as usual with these old scopes start by measuring the supply voltages and ripple. If it is in spec according to the service manual you can try to see how much out of calibration it is.
Do all the measurements after some 15min of warmup time.
Depending on storage conditions it might need a bit of a cleaning...

[wn1fju]

I usually don't change electrolytics as a matter of course unless I see leakage or there is excessive ripple on a particular power rail.  With the 465, you are more likely to have problems with the tantalum capacitors which will short and bring the rail down near zero.  Make sure you check the power supplies with a scope, not just a DC voltmeter.

Also with these scopes, the pots and switches will need a thorough cleaning with your favorite contact cleaner.  Be prepared to dissect the two attenuator cam mechanisms and clean the spring contacts with alcohol.

As is the case with many vintage Tektronix scopes, disassembly is a bit of a chore, but everything is logically organized.

[xrunner]

I see a lot of nasty corrosion on the front - screws, BNCs, the right side under the front bezel. I sure hope you don't see that kind of corrosion inside. You might want to open it up now and see what it looks like. It might change your mind ...

Good luck on it.

[Kevwr]

Yes, this unit is in quite bad shape as the container was missing its lid and it was stored badly. But the good news is that I picked up 2 465M’s and the other one is in pristine cosmetic condition,
I only bought this one for spares due to its condition but it has a nice trace whereas the good looking one does not. Between the 2 I’m hoping to be able to get one restored and functioning.

[Kevwr]

I managed to download the manual and I’m impressed. It’s very comprehensive and has a great fault finding schematic which as expected has the power supply as the first area to check.

[Kevwr]

I usually don't change electrolytics as a matter of course unless I see leakage or there is excessive ripple on a particular power rail.  With the 465, you are more likely to have problems with the tantalum capacitors which will short and bring the rail down near zero.  Make sure you check the power supplies with a scope, not just a DC voltmeter.

Also with these scopes, the pots and switches will need a thorough cleaning with your favorite contact cleaner.  Be prepared to dissect the two attenuator cam mechanisms and clean the spring contacts with alcohol.

As is the case with many vintage Tektronix scopes, disassembly is a bit of a chore, but everything is logically organized.

This is the military version 465M and looks like it’s been designed for easier disassembly in modules. I’ve read that it’s closer to a 455 than a 456 in design.
You say to use a an oscilloscope when checking the power supply lines, is that for ripple? I’ve watched a few YouTube videos on restoration and quite a few tantalum caps were shorted and replaced with electrolytics.

[wn1fju]

I've just gotten in the habit of checking the power rails with a scope after measuring them with a DC voltmeter.  It only takes a couple of minutes.  What you want to avoid is a situation where the DC voltmeter, which smooths out any fluctuations, leads you into a false sense of security.  The scope will easily see 60 Hz fluctuations (diodes), 120 Hz fluctuations (main filter caps) and high frequency oscillations (regulator problems).  I've come across a few repairs where the DC voltage was "almost" correct, but the scope trace instantly told me what was likely wrong.

The only time I don't probe with a scope is when I'm fixing the primary side of a switching power supply.  If you don't know why that is dangerous (without an isolation transformer), then you shouldn't be doing it anyway.