Rebuilding my old analog console

Mixedgas: thanks for the reply. I'll check the phases on the oscillators. I'm using teflon caps and polystyrene caps. I did not check for matched capacitance values though. Funny thing is that i still the the original paper datasheet for the 4423 with notes I wrote on it that I do not remember writing.

I will need go back and check my signal path. I thought I was running the same sin/cos signal from a single oscillator to both scan pairs. In which case I would expect both to produce round circles. But your comment made me think that maybe that wasn't the case and one of the oscillators is misbehaving.

I am perplexed with this balance issue and if I had enough hair I would be pulling it out. :D BUT this is one of the main reasons for doing this stuff - the true joy of learning how things work and problem solving.

Summary: both scan sets are getting the same singal from a single 4423. I swapped the summing amps and the issue did not move to the other scan set. I swapped the scan amp outputs to the scan sets and the issue did not move to the other scan set.

When I get home from work, I'm going to swap the scan set at the galvo leads and see what happens.

I tested 8 galvos and none of them produced an image as clean as this one scan set, which was surprising. Some of them produced less of an oval but no circles. I think I will also switch out one of the galvos from the good scan set and see what happens.

Based on your "swappings" experiements, it points to differences in scanner pair responses to your amplified XY signals. G115/120 open-loop scanners all had ever so slight phase response differences, most were negligible but apparent. It could be anything from differences of mirror masses to bearing wear (or contamination) to changes in the torsion springs behaviors.

You never mentioned but how are your four coil wires connected to the drive amps. The two scanner coils are commonly connected in parallel. Check the coil connections between each scanner and their drive amp. Any funky connections?

Lasermaster1977: that makes a lot of sense.

Wiring: red/green paired and black/yellow paired.

With an improved scan amp circuit with some feedback, can some of that be compensated for or tweaked out?

Quote:

---

Originally Posted by Kevint

Lasermaster1977: that makes a lot of sense.

Wiring: red/green paired and black/yellow paired.

With an improved scan amp circuit with some feedback, can some of that be compensated for or tweaked out?

---

Okay, that's like my G-115 coils are paired. The two coils are wired in parallel.

That is difficult to say whether improved scan amp circuitry will help, much depends on the root cause.

What are your mirror sizes and thickness? Are all mirror mounts the same size and type?

I can offer that once I had a similar issue and it turned out to be a scan mirror glue started to fail. Replacing that mirror/mount fixed the issue and once the original mirror was removed from its mount, the mount cleaned and the mirror re-glued, all was good again.

I don't recall if you mentioned whether the phase difference in the one pair occurs at most XY frequencies or at a specific, narrow frequency range. It would interesting (and possibly helpful) to know how the circle's phase shift varies as the circle's frequency changes from low to high, e.g. 30 Hz to 500 Hz, at say half the maximum optical scan angle.

Lasermaster1977: good point. Since I am prototyping I haven't been giving much attention to standardizing mirrors and mount for consistancy, just using what I got laying around. I did purchase some scan mirrors on ebay last night 7.0mmx11.0mmx0.75mm, but I am limited on mirror mounts and would have to finad a source to purchase from. The oval phase does shift are the frequency is adjusted. I'll take a video of that in action and post.

Quote:

---

Originally Posted by Kevint

Lasermaster1977: good point. Since I am prototyping I haven't been giving much attention to standardizing mirrors and mount for consistancy, just using what I got laying around. I did purchase some scan mirrors on ebay last night 7.0mmx11.0mmx0.75mm, but I am limited on mirror mounts and would have to finad a source to purchase from. The oval phase does shift are the frequency is adjusted. I'll take a video of that in action and post.

---

Mirror standardization is important. Normally, those mirrors and mounts acquired from General Scanning, the X mirror would be a 7mm x 7mm x 1mm and the Y mirror would be 7mm x 11mm x 1mm.
Here is a photo showing these mirrors and their mounts. I've posted these and other photos on this forum in the past.

Attachment 60970

These are examples of the two types of General Scanning mirror mounts that I have. The larger mount at the left is what originally came with my G-115's, the smaller ones (lower mass) were offered a bit later for the G-120PDs. (these mirrors shown are ones I got from a laser friend who kept them in a hot garage in Texas for many years.)

Attachment 60973 Attachment 60971 Attachment 60972

If you heat the back of the mount with a soldering iron the epoxy will melt and the mirror flicks off with a pair of pliars... Take the set screw out first. Keep the mounts, no one has made G style aluminum mounts in a decade or more.

There is a wire drill size that corresponds to the galvo shaft. Ordering that bit provides a handle for mirror removal or mounting off the galvo. The 0.499 galvo base fits in a
assortment available post mounts, the Thorlabs RA90 being one of my go to tools for GSI galvos.


I'm the one that sold the galvos to G. I tested the coils and made sure the T-bars were intact, that is as far as I went.

Your newer but used galvos were in the Triton Planetarium outside Chicago in a four head projector, if you bought what I think you did. They ran closed loop on some old G100 style GSI designed amplifiers that had a really dinky feedback system.

Steve

Quote:

---

Originally Posted by mixedgas

I'm the one that sold the galvos to G. I tested the coils and made sure the T-bars were intact, that is as far as I went.

Your newer but used galvos were in the Triton Planetarium outside Chicago in a four head projector, if you bought what I think you did. They ran closed loop on some old G100 style GSI designed amplifiers that had a really dinky feedback system.

---

True dat, but I included an extra pair of the same model of galvo that came from a company called Light Construction, that was Canada's first something-or-other laser graphics something-or-other. The galvos were mixed up when I sent them and I couldn't tell which was which, but that might have bearing on the noticed performance difference with two of the galvos. I have a big over specd XY mount for those if anyone wants it.

There's a photo of the XY mount with the extra 2 galvos you have on page 24 of CYGN-B.