I recently started repairing this Northstar CT-1000 Digital Flight Bag computer from 1989. The computer is based on a Cell Computing module that were kind of like the Raspberry Pi compute modules of their time.

Unfortunately the power supply in its home docking unit aged out and in turn took out the main power supply in the dock.

After checking the capacitors in circuit using the Peak Atlas LCR45 Passive Component Analyzer (not shown), I temporally replaced the 3A fuse (upper left). I set my bench power supply to 1.5A and then powered on the power supply. During that time the power supply clamped into constant current (CC) mode indicating that a short still existed in the supply under test.

In the photo the Transient-voltage-suppression diode (far upper left) caused the fuse to heat up. I was able to verify this using a handheld thermal camera (not shown). By lifting one side of the TVS and the powering the bench supply back on, It no longer was in CC mode. This provided proof that the TVS failed (crowbared) and protected the rest of the computer from damage.

Right now I am waiting on an order from Digikey to replace the dead TVS. I went ahead and used my desoldering gun (not shown) and replaced the primary CMOS battery since it was long dead.

It is a rather unique chemistry, lithium thionyl chloride (Li/SOCl₂).

I will make an update on the repair process as soon as I get the next part I need.

Please take care of each other.