Mitsubishi MBE90K Sensor Adjustment

[bigpappy]

Hello all, I must start out by saying that as a mechanical engineer I am out of my element over here so please don't mind any silly questions.

Long story to follow, I own a small machine shop and my CNC turning center is having some threading feedback issues.
I've already been on the phone with the manufacturer, Mazak, and they handed me off to Mitsubishi Electric Automation as it is their "package" that is out of whack.
This "package" or the MBE90K consists of two gears, two sensors, and a pre-amplifier, all of which control the C-axis, speed feedback, and spindle orientation.
After speaking with a tech, we were able to narrow my issues down to the pre-amp and I was able to get a step-by-step adjustment manual from them.

Basically, I needed to adjust the waveforms of each pulse and phase to match the stock configuration and be within the required tolerances.
For example my threading issue has to do with the X-pulse which is for orientation.
"The pulse width of the X-pulse needs to be 65-75% of the period of the F-phase. The rising edge of the X-pulse needs to rise before the start of the F-phase sine wave. The distance between the rising edge of the X-pulse and the start of the F-phase needs to be 5-10% of the period of the F-phase...."
This is all adjusted with multiple little knobs on the board.

This all sounded a bit out of my league and I do not have oscilloscope at my disposal so I had a private tech come out to do the adjusting.
Well he adjusted everything right at the edge of the allowed tolerances, so once the machine heats up and gets rolling, the tolerances get blown and the pre-amp sends jumbled signals to the controller.
For the cost of him to come out again I can purchase the Rigol DS1054Z or equivalent and be money ahead.

My question is, how do I know what bandwidth I need on the o-scope to measure and adjust the pre-amp properly, i.e. I don't want to buy more than I need, but also don't want to get stuck with something that won't work.
I asked Mitsubishi that question and they had no idea, he said they just use some high end expensive fluke to do everything they need.
No mention of specs or model numbers.
From some of the research I've done, it seems the frequency of the circuit being tested is usually a known variable before starting.
What are you supposed to do for completely unknown circuits?

I apologize for the long winded post, but I figured I would give you the whole story!
Thanks in advance for any help.

[wraper]

If it drifts while heating up / over time, I suspect there might be some fault. Therefore repair might be needed, not adjustment.