The most infamous feature of late 80’s Tek scopes seems to be the battery-preserved calibration ram. When the battery dies, the calibration is gone. DIY calibration is out of the question, and it is not likely for me to pay hundreds of dollars to get my 30+ year old scope calibrated, no matter how beloved. This being said, the stakes are high.

My scope is one of the earlier production models, and as such it has a battery external to the calibration ram chip. Later models have a Texas Instruments chip with an internal battery. Accordingly, the procedure I intend to follow is described on a similar model here. As a backup plan, I entered the scope’s diagnostic mode and recorded my findings of the “Exerciser 02” routine, described in the manual below.

I took a video of the screen while I flipped through all 256 values. It will be my last line of defense if I end up losing the calibration data. I would probably have to pop the ram chip in a programmer and enter each value manually. All this while maintaining power to it? Not ideal. Here we go.

I prepared a battery holder with 2 AA batteries. The original positive wire actually had a intermittent connection. It goes to show that its always good to take readings.

I soldered the positive and negative wires to the cathodes of CR2770 and C2470 respectively. The cathode of C2470 is tough to see in the picture. It is the leg of the capacitor facing away from the battery.

With only 4 legs, the battery was easy to wiggle out. I was concerned about the whole grounding issue with the soldering iron, but I felt fairly confident the problem would be mitigated by my use of batteries.

Time to re-assemble. I would test it out of the case, but I’ve read a lot about how it is specially designed to channel air over high-heat chips. Why risk it? Getting it back in it’s case is quite a pain and I cannot seem to get any better at lining up the front plate and the ridges of the case. It would be easier with the front cover. I was thinking of buying one as a reward to myself if this is successful.

I hadn’t been filled with so much anxiety since I clogged the toilet in my first girlfriend’s crowded family apartment. Luckily, this time I was in the clear.

I printed out a note to put in the pouch for the oscilloscope, so I or any future owner can see when the next replacement is due. I did it using a 1983 IBM PCJr I’ve been working on that someone decided was recycling. Even with its IBM parallel dot matrix printer!