GF not staying in focus and it's not the print head

[sqw]

I have two machines. Cutting the same file on each, one works perfectly. The other starts out with correct focus, but then loses it part way through. The beam goes from sharp cutting, to blurred and wide and no cut through.

I have swapped the print heads (complete with lens etc) between the two machines and the problem remains on the same machine, so it is not the print head.

It is not the lens in wrong way round etc - because I swapped the print heads complete.

The prints are using default cut settings for draftboard.

I have checked and cleaned all the rails at sides and on gantry, can find nothing on the rails or the belts. I have cleaned the optics under left hand side.

The head is moving the lens. During the focussing phase the lens moves in and out.

So, the issue is printer specific and swapping print heads did not resolve the problem.

[geek2nurse]

Save yourself some time by printing and photographing the requisite Gift of Good Measure on PG test.

[sqw]

Good shout, but is confusing in itself. The GoGM prints OK. Which fits my earlier symptoms, the focus gets lost part way through.

There is not a change of cut settings - this is all on single cut setting - proofgrade. So it’s going wonky part way through one range.

It’s not the file, because printing that on my other GF works fine.

[sqw]

Is it a dodgy white cable causing the unit to refocus during the cut?