This particular analyzer is one of our favorites to work on (repair).
Here is a list of some of our checks that we perform before we release your analyzer for shipment:
Noise on range X1 should be minimal (±1 count)
All ranges should be correlated (especially those with an optional range trim board)
Response to certified calibration gas should be equal to or better than factory specfications
When TP5 = 5 VDC then [a] the display reads 100.00,  analog output is either 100mV or 1V or 5V (depending on jumper configuration,  isolated current output = 20 mADC
Analyzer is clean
Insulation is reglued
Frayed wires are fixed
Plexiglass is grounded
A/C power switch leads are coated with “liquid electrical tape” insulation
Ribbon cables are pristine
Rear terminal strip has a sticker that shows what functions are on what terminals
Zero pot (potentiometer) is greater than 50% (the higher the number here, the less contamination in the analyzer tubing)
It needs to look good again (paint job if necessary)
Flame saftey circuits MUST work properly
Backpressure regulator works as designed (and controls a a very reliable value)
There’s a bunch more, but I don’t want to bore you with the entire list!
Give us a try!