Scanning (maybe) issue?

[norty303]

Hi All

I've got a laser I built back for inspection because it has started scanning badly. The image is shifted way over to the left and the output as you will see in the video is terrible.
The video starts at 30kpps and goes down to 6kpps when it looks much cleaner. I've checked the scanner PSU and its giving +24V and -24V under load.

Could it be poly switches, or could the galvos have been overdriven? At 6kpps it almost looks like it just needs a bit of a tune up. I've been assured that nobody has fiddled with the amp pots.

Appreciate any advice you can give on where to check next. It is using PT-A40 scanners.



https://youtu.be/yc6Gjqc7lEw

[absolom7691]

Definitely looks like poly switch to me. I would try throwing a fuse across the poly switch and see if that clears it up. If you're pulling too much current for some reason, at least the fuse will blow before you damage anything.

[norty303]

Shouldn't poly switches reset on a power cycle though? This is like it all the time.

[absolom7691]

They can go bad. They also have a finite lifespan.

[norty303]

I bridged across the polyswitch and nothing changed so I guess they're ok.
Even with no signal connected to the amps the X galvo comes to rest a long way off centre so I suspect it could be a damaged position sensor, or position feedback on the amp, or simply damaged galvo.
I've wiggled all of the pots on the amps to make sure none of those have gone dirty, as I had that once before.

[absolom7691]

Based on your findings, I would agree. It sounds like there is something going on with the sensor. I am sure you've tried this... swap scanner cables?

[mixedgas]

Based on your findings, I would agree. It sounds like there is something going on with the sensor. I am sure you've tried this... swap scanner cables?

If your power supplies are solid and producing clean DC, then You've experienced a failure of one of the components on the amplifier.
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Disconnect one amp, and scan the laser. Supply a fan of dots say 5, like a effects beam frame, spaced about 5 degrees apart, and post the picture. The goal is to scan the dots at about 30-40 Hz.
Disconnect that amp, switch to the other amp, and scan the same frame rotated 90 degrees.
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This way I can get a look at the overshoot and undershoot and artifacts and see if I can spot which part of the circuit is out.
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Ideally you'd test the amp with a ppoint based quad square or 30 Hz Square wave, too....
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On the bench we use square waves and triangle waves for galvo amp and position sensor testing. It makes it easier to recognize faults. For this we use a bench signal generator, NOT laser show software. That removes any chance of any software timing issues or vector conversion or point smoothing or optimization whatever from the software decision process.
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Check the +/- 15 Volt regulators by measuring with a voltmeter to amp board ground. The pinouts are widely available in pdf datasheets for the parts, which are typically LM7815 and LM7915.
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Are these well heatsinked? Failure to heatsink can do this as well, especially on clone amps where the coil temperature shutdown circuit has been omitted.
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Do you have an oscilloscope?
!
Steve

[norty303]

Hi Steve

Thanks for all that. No I don't have a scope.

I think that there is a problem with the actual galvo as even when I swap amps, the position is still skewed over to the left.
I would imagine that an amp problem wouldn't cause exactly the same positional issue. Even if both were faulty in exactly the way, I'd see a shift in the Y axis too, and I don't.