Ruida RDC6445G+Synrad RF tube troubleshooting. Start of cut not firing.

[Didrik Madheden]

I'm retrofitting a laser engraver from Universal Laser Systems at my local makerspace. The original electronics were discarded by someone else, so sorry, no vendor files. I've attached overview pictures just so you can get an idea of the project. The machine came with a Synrad 48-2 series RF excited tube. (Attached photo of label.) To this, I've added a Ruida RDC6445G(EC) controller, running firmware V15.01.19 after upgrading.

This is supposed to be a square cut clockwise, but as you can see, the laser isn't firing during the start of the cut. These tests are made using RDWorks, 100% power (both min and max) and 20 mm/s speed. I've tried changing the tickle frequency and percentage, but to no avail. (I'm currently also trying engraving which isn't looking too good, will be posting in a bit when that's done.) Any idea how to approach this? Is the tube knackered or is there any chance of getting it working properly? It does output laser power, so I'm hoping this is a fixable electronics or control issue.

IMG20250828000508.jpg

[Didrik Madheden]

Engraving test. This is of our makerspace's logo, with settings 40%/1500 mm/s, 70%/40 mm/s, 70%/150 mm/s as noted on the test piece. These are produced from a bitmap using Lightburn this time, using threshold, ie no dithering. The laser seems to fire at the very start of each line, then disappear, then come back slightly later during the line. I have to say on a positive note, that if I was trying to make a cut as fine the outline that is produced here, (70%/40 mm/s in particular) I'd be very happy.

[Didrik Madheden]

Well, it turns out the issue with the complete failure to lase was with the laser frequency. I had set it to 20 kHz thinking higher was better for resolution. This was not really the case. Even 5 kHz was seemingly too much. These examples were made with 2 kHz laser frequency and 5 kHz pre-ignition frequency. Much better quality over all, but still not perfect. With 20% power, I still get obvious dropouts like this similar to the previous issue. At 30% I get a quality that's much more even consistent, however I still get dropouts where the laser tube just stops lasing, with the solution being to cycle the power to the tube.

It seems like this kind of tube is very fuzzy about what signals it accepts. I'm also noting that the way that Universal designed the unit, the 120 V power supply to the tube was connected with an electronic relay. This suggests to me that maybe they intended for it to be cycled often, maybe between every line. Does anyone have more insights into how these tubes are optimally driven? Does anyone have a similar Universal Laser Systems machine with the original electronics intact? I'd be interested in the ROM dumps from that device for further analysis.

Also, does anyone have experience with opening up a Synrad tube to inspect the electronics. I would try it, but I don't want to let the the CO2 out and ruin the tube.