Fixing the fixing machine

OK, I will admit that I’ve got a hangup on old analog Oscilloscopes these days.

Tektronix is especially one of my favorites, and I gather these are considered the best there is among analog scopes.

So I currently have aquired five Oscilloscopes. Three of these are Tektronix, one 454A and two 2445.

But all of these need some love and care. The thing is that the electrolytic capacitors in any old electronic equipment will start to leak and go bad over time. Excessive capacitor ESR is one of the most common causes of bad circuit behaviors

Of course the state you will find these secondhand will also heavily depend on how they have been stored. IE. in a garage or in an attic, with potential humid condensation and fungi.

My two Tek 2445 were both manufactured 1983 and the serialnumbers show that they are only 149 units apart in the produciton line in Portland, Oregon.

Bad behaviour

So first thing first, if you at all dare to power them on, you might experience some “magic smoke” and you might experience other irregularitues like missing readouts etc.

Some say you should never power them on until all capacitors are changed, because of the fact that any defect in these components could cause even bigger damage to other components like IC chips that are hard to get a hold of.

So my approach was to fire it up, and fire it did!

Magic smoke escaped from the Rifa capacitors on first power zapped and smoked good
Blown Rifa, a very common error on old units
Old leaking capacitor. These can leak in terms of physical leakage, they can also leak electronically in terms of not keeping their capacitance.

Next step

Get a hold of a capacitor kit for your unit. Allthough you could try sourcing these by regular means, these units are presicion intstruments that needs specific types of capacitors like the Panasonic FR series and high quality Nichicon caps.

I contacted Yachad Menahem from Israel, through and received a perfect kit for both of my Tek scopes after a couple of weeks.

First out the powersupply on these units needs to be dead on stable so this is allways a good start.

A2 Regulator board
A3 board, swapping out the big Mallory axial caps with inline caps
Some modification was needed for these to fit in the enclosure
It’s all in the details..
Working on the A1 Main board
Detaching and re-mounting the A1 board was probably the trickiest part of this restoration. Lots of things to look out for in order not to damage..Easy does it every time
Watch out for the furious CRT tube as the stored Voltage in this is over 7000V and can easily kill you.

If messing with this, make sure to discharge it by carefully opening the red wire connection shown in this picture and discharge it via the chassis


About 40-50 caps where changed on the A1, A2, A3, A5 and A9 board
Find the manual and probe the 9 test points to see if the Voltages are within spec
All diagnostic tests pass, a good sign!
The brothers are alive and kicking again, 39 years old! They are truly some beautiles. Notice the cosmetic fix on the 4 left knobs on the right scope. I 3D printed these as the old ones broke upon disassembly.

Recommended resources:

The inner beauty of a Sine curve:

The Unit circle

The Phase Shift

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