Odd galvo issue

[Things]

Recently I've started having an odd issue with my projector. Here is a video:



As you can see, the whole image seems to be expanding/shrinking/wobbling randomly.

A few points:

1. This has been happening for a while, and I have NOT changed any wiring in my projector since.
2. It only does it randomly. Sometimes it'll be fine, sometimes it'll have a slight wobble only visible up close, and other times it'll completely freak out like in that video.
3. It does not seem to be affected by how long I leave the projector running - It can happen right at start up too.
4. I have tested my main power supply rails, and the + rail is practically ripple free, The - rail seems to have a slight ripple, about 200mV that repeats fairly regularly



5. I have tried it with the DAC on a laptop and a desktop - No difference.
6. Nothing seems to be getting abnormally hot.
7. My galvo's are DT25's and DAC is a FB3.

I'm really lost on what to try now. Is it possible that maybe my galvos are going into oscillation from tuning? Would it happen sporadically like that, or all the time if it was tuning oscillations? Would the ~200mV ripple on the - rail be of any concern?

Cheers,
Dan

[DZ]

Hi Dan,

I doubt the issue is tuning since it appears to be occuring on both galvo's at the same time. It's been a while since I've messed with a set of DT-25's but I remember that they had a single amp that handled X and Y but it was essentially 2 amps on 1 card. If I remember correctly, the power supply is +/-24V and the amp has an onboard 7815 and 7915 regulators. So regardless of the ripple you're seeing on the main supply, the amp drops this down to +/-15V (IIRC). You could look at the output of the regulators to make sure they are stable. I see from the pic above that you have a scope, does it have an X/Y setting? Have you looked at the output of the FB3? What all is between the FB3 and the scanner amp? I'm guessing at least an ILDA cable to a DB25 in the projector and wires directly to the amp? Do you have ILDA pin 25 connected to the amp or to the power supply?

[laserist]

Unless I'm mistaken the on board regulators only supply the opamps and the higher voltage still supplies the Galvo amp. I'd be looking really hard for a bad connection. I really couldn't tell from the Video if the problem is in both axes. If not a noisy pot could generate that sort of problem...

[taggalucci]

What is your ground wiring scheme for AC, also DC, and how is pin 25 connected within the projector?

[Things]

Thanks all for the replies

I realized I have a spare PSU in my laser harp, I'll give that a try just to eliminate the PSU from the question (Or find the issue).

Hi Dan,

I doubt the issue is tuning since it appears to be occuring on both galvo's at the same time. It's been a while since I've messed with a set of DT-25's but I remember that they had a single amp that handled X and Y but it was essentially 2 amps on 1 card. If I remember correctly, the power supply is +/-24V and the amp has an onboard 7815 and 7915 regulators. So regardless of the ripple you're seeing on the main supply, the amp drops this down to +/-15V (IIRC). You could look at the output of the regulators to make sure they are stable. I see from the pic above that you have a scope, does it have an X/Y setting? Have you looked at the output of the FB3? What all is between the FB3 and the scanner amp? I'm guessing at least an ILDA cable to a DB25 in the projector and wires directly to the amp? Do you have ILDA pin 25 connected to the amp or to the power supply?

Correct, both amps are on the same card, however they use s single audio amplifier chip between them. I will see about measuring the voltage regulators.
Unfortunately the scope is just a cheap pocket scope, so it only has 1 channel. I did have it connected to the FB3 and didn't really see any issue from what I had.

The FB3 is connected thru a 1M DB25 which terminates to one of your older ILDA breakout boards.

As for the grounds, I tried to keep signal and mains ground isolated from each other, though it seems there's a connection on the breakout board somewhere (maybe the DB25 shell?), so signal ground is connected to mains ground. All my other grounds connect at the same terminal on the galvo PSU.

Unless I'm mistaken the on board regulators only supply the opamps and the higher voltage still supplies the Galvo amp. I'd be looking really hard for a bad connection. I really couldn't tell from the Video if the problem is in both axes. If not a noisy pot could generate that sort of problem...

I have tried wiggling a few wires around and nothing really seemed to change. I'll keep looking though as that would be the best scenario for me here. I was also thinking maybe a noisy pot, but it happens on both axes so I'm not sure.

What is your ground wiring scheme for AC, also DC, and how is pin 25 connected within the projector?

As I said to DZ above, all my grounds are connected to the galvo PSU's FG. However, my signal ground is connected to mains ground somewhere unintentionally.

Dan

[taggalucci]

As I said to DZ above, all my grounds are connected to the galvo PSU's FG. However, my signal ground is connected to mains ground somewhere unintentionally.

Hi Dan,

2 possible sources of the DC ground and AC ground being bridged is the DPSS housing on some modules, or the galvo block. If you use a meter and run a continuity test, you should not get a reading between your DC ground and each DPSS housing, or AC ground and galvo block.

I'd start with isolating the galvo block first (assuming it's mounted to a metal panel which is earthed).

[Things]

The thing is, it has been wired that way it's entire life and I've never had any issues with it like that. This has only started happening recently (Within the last 2 months or so).

Dan

[Things]

OK well, I put the PSU out of my laser harp in and so far it looks promising. Image is absolutely rock solid at the moment.

Going to leave it for a while and see what happens.

The bad part is, these +/-24V power supplies are almost unobtainium

[Things]

So, I replaced the - rail capacitors in my power supply and it seems to have fixed the wobbling line issue. However, I noticed the image still trying to collapse on itself sometimes, however only in 1 direction. I checked my breakout board and there was 1 loose screw terminal.

So it seems like it was the loose wire causing the larger jittering, and the PSU ripple causing rippling in the lines.

All good so far. Giving it a bit of a burn in now to see if it keeps that way.

Dan