HP 41 Repair for inexperienced owner

[dbhp67]

Hi,

I recently bought an inexpensive non working HP41CV which is in good cosmetic condition. I have done some research and had a look at the repairing book that is available. However I could do with some help in diagnosing what may be wrong with it.

So far I have:
1. Disassembled it. I have then checked the batteries are making a connection to the correct contact on the power connector. From memory I get 2x1.5V on line 3 and another 2x1.5v on one of the middle lines. So i am confident the battery is providing power to the main board.

2. I have checked for continuity wherever I could see any corrosion - there isn’t much, and there is a circuit working in each case.

3. Is there anything else that might be a common failure that I can check with a multimeter?

I have not unscrewed the nut to check the Zebra, but just looking at it it seems very secure. I could try spraying some contact cleaner in there if that might help.

Does anyone have any suggestions as to how best to diagnose a fault, then i can replace whatever i might need....

Many thanks in advance
DB