My right hand fell off

There goes the saying you don’t know what you have until you lose it. One day my Tektronix Oscilloscope started to misbehave. It is one of the last of its kind. It is analogue at heart but computer controlled. Sort of hybrid between the old days and the days to come.

I haven’t really appreciated how good tool it still is despite it’s age up until it broke down. While the digital scope I have is super powerful and packed with intelligence this machine is just so much quicker to use and the reading gives you immediate idea about what is going on.

I was forced to take a break from all my day to day repairs and dwell into the world of unknown. I never worked on oscilloscope before and I never worked on anything with CRT screen where several kilovolts are present. While the service manual is exceptionally thorough in test procedures and calibration steps it doesn’t really tell you where to look when tests fail or something is not as expected.

I was very fortunate to find internet group of enthusiasts on who live and breathe vintage Tek scopes. The level of knowledge in that group is mind blowing. Some of the original design engineers are there and continue improving and supporting those ancient beauties.

There were two possible causes for my problem. One was leaked capacitors on the A5 computer logic board cause corrosion and key reference voltages end up all over the place. My oscilloscope had these leaked but the damage was not yet severe. It was caught the last minute I’d say.

I had to remove all the smd components in vicinity, thoroughly clean the PCB with demineralised water and activated flux in several rounds to ensure there is no residue of the electrolyte. Next was inspection under microscope, removal of the mask where traces already started to corrode, repair of the traces, new application of solder mask and finally put back the components.

It was solid 11 hours of surgical work but the outcome was good.

Since Tek used tantalum caps in later revisions which don’t tend to leak or go bad I replaced the original SMD aluminium electrolytics with tantalum caps.

When all this was completed I to my surprise found out the problem remains the same . The root cause was failed hybrid chip in charge of mixing signals from all 4 inputs as well as readout generator together before it’s sent to final vertical amp stage and CRT.

I’m very happy to have the Tek 2445B back in shape once more.