These circuits are simple SMT 4 pad 12Mhz crystals with currently 2x 22pF caps to Gnd, and crystal directly into a microcontroller of sorts, that run between 40Mhz and 80Mhz, depending on the product they are in.
Based on the reading I have done, the loading caps (currently 22pF) should be selected based on a formula similar to
Caps = 2x CL - Cstray
Where Cstray is somewhere between 2-5pF, and CL comes from the Crystal datasheet.
I then found variations on this, where its 2x CL - 2x Cstray
And then another variation which ends up much the same as the second one, which is CL = ((Cap x Cap) / (Cap + Cap)) + Cstray
Either way, the current values we have been using I am imagining are on the fridge of being correct now, and are not ideal at all. Assuming those formulas are anything like being correct.
22pF was selected way back in 2010 and the supplier of the crystals has changed a few times, and staff also have changed, so the spec has somewhat slipped.
Looking on the scope, one product the scope loads down to about 400Hz instead of 12Mhz, but the sine wave is beautiful. Another one also loads it down about the same, but the Sine wave is not very Sine wavey at all. Another product it loads it down to 1.2Khz and is also beautiful. So I really just want to see what its like when its running at 12Mhz if I can, to hopefully then be able to judge which is a 'better' cap, if we have a few variants side by side and view them all.
Money is an issue, and so is time, so I would prefer to be able to just get a 100x probe off the shelf and quickly see if we are in the right zone. Active probe is cost-prohibitive, as is building a circuit I think (although this would be neat to try next if the probe doesnt do what I want). Because its all low voltage I deal with, many of these probes seem specific to HV stuff, which I guess is where the $$ comes in.