Battery

This is what can happen when a battery, in poor condition, leaks:

In most of the Mark V's I have serviced, I have found the battery leaking, and damage to the PCB. If your Mark V still has the original NiCd battery, it's over 30 years old, and most likely ruined. It is advisable to replace it, or at the very least, remove it.

An important thing to note about the SciSys Mark V: the battery only recharges while the computer is switched on. It is not enough that the external adapter is plugged in.