Coherent VersaPulse VPW - what should I do with it?

[TMaxElectronics]

Sooo back form a long phase of missing motivation due to exams not going the way I wanted to and getting bored with uni I thought it'd finally be time to play in the workshop again. And I just happened to get a Coherent Versapulse NdYag Laser that a local hospital was throwing out for a grand sum of 0€

I'll talk about how i fixed it in the rest of this post, but the main question I'm asking myself is: what the hell should I do with it??? It's way too beautiful to scrap for parts, but I have exactly no ideas what to do with it. Maybe a nice in-depth non-destructive teardown?

Thats the beast (slightly modified with that front switch... I'll get to that later)


According to the Label its a pulsed (flashlamp) NdYag, frequency doubled to 532nm. No Q-Switch unfortunately, but hence quite a long maximum pulse length of 100ms.


The first problem I had was how to get it down into my basement, as the thing easily weighs 200kg. Luckily it's made to be serviceable and thus I was able to take off the side panels, the front door and the lamp supply fairly easily. The front door alone is made from 10mm solid die-cast aluminium and (together with the screen) probably weights 25kg just on its own. Same with the handles and cable holder which appear to be solid cast as well.


Unfortunately the unit was unhappy with my treatment (or possibly with how it was treated at the hospital before I got it) and didn't even give me a user interface on the screen. Just some cryptic error codes, along with a nicely misaligned text header due to the display not knowing what a character 'ä' is and inserting a line break.

Incidentally the monitor is just a fancy serial terminal, as the text that it displays get sent to it over UART in ASCII.

A bit of fault finding (along with the use of a suspicious switch labeled "service", which allowed me to get to the UI even with the faults present and read what the errors actually mean) told me that it was missing coolant pressure/flow, that "the power supply did not calibrate" and something was wrong with a crowbar circuit inside it.

The error regarding the lack of coolant flow came from a seized pump, which I had to un-seize with the power drill. Moving it a bunch seemed to eventually get it moving smoothly again. Fun fact: the pump alone is 1/2 hp and draws 2A continuously.

That fixed the coolant error.

Taking a closer look at the high voltage power supply shows a common architecture for NdYag flashlamp drivers. The (single phase) power input gets rectified and goes straight into a boost pfc stage (marked in red), which then charges the main capacitor bank. From there you have one big IGBT connecting the flashlamp across the bank (the top one of the two) and a diode network one the top right of the heatsink. This is also where the crowbar circuit lives, which I didn't actually find a purpose for if I'm honest. It's kind of self triggered, but can also be triggered externally, and is connected behind the diodes which go to the flashlamp, so almost across it but not really.


But what about the crowbar fault? The service manual of a similar laser which uses the same power supply states that the crowbar is fired during self test and the controller gets a light pulse through one of the 9 fiber optic control links to tell it that the crowbar fired successfully. If it doesn't get that it will fail the self test. In the end the error turned out to not be circuitry related but instead a previous service tech, that must have been a bit eager to get the fibers disconnected from the controller as one was loose inside the crimped on connector. Pushing that back in fixed the other two errors

Talking about the controller, it's quite an old design (the laser itself dates from around 1997) but has a crazy amount of redundancy and fail safes built in.

On the top left are the fiber optic connections to the lamp supply and top right are the cables going to the optics module.
It has two (!) Motorola 68 030 cpu's running independently of each other. One is the main/control cpu and the other is just there as a safety processor. It monitors every move of the main processor (including if the software has crashed) and if it dislikes it even one bit it will immediately kill the power to the unit.
Interestingly enough it also independently measures the delivered beam energy and if the two processors disagree the laser shuts down immediately as well. Reminds me of that Therac-25 story, where a computer glitch caused massive radiation doses to be delivered.
The daughter board with the large opto isolators is for the footswitch and other external connections. Interestingly enough it even monitors cable integrity in the footswitch and won't turn on unless the cable is undamaged.
There are also service ports on the right side of the board, with rs232 transceivers next to them but no data is sent. They probably require some command to enable them.
And finally there is a speaker for beep sounds down the bottom. They sound exactly like those that old cash registers make when you scan a barcode which gave me flashbacks of going grocery shopping with my mom lol.

Oh and what does the front switch do? It's a service mode enable that I can reach without opening the front of the machine
You can turn up the pulse energy quite a bit more when in service mode

[Twospoons]

I am amazed you got that for nothing.  A medical grade laser would be a seriously expensive piece of kit, given all the regulatory hoops that the manufacturer would have to go through.
7.5J per pulse is pretty substantial - probably good enough for marking, or even cutting if the rep rate is high enough.

[TMaxElectronics]

I guess it was just not worth fixing anymore, as Coherent stopped supporting the machine and the company that supposedly took over servicing doesn't seem to give a damn about getting such an old unit fixed. At least they wouldn't send a service manual or even tell me who to contact for a quote to get the laser fixed. Then again the machine is pretty much 25 years old by now and has been superseded by much more efficient and modern diode lasers. The machine draws 2kW even when just simmering the lamp

Judging by the coolant level the machine wouldn't have been run for at least a few years (the tank was only about 3/4 full, and only diffusion would have emptied that). So they probably just wanted it out of the way and were happy to find somebody that could do something with it. Oh and knowing a technician at the hospital was probably helpful too

Issue is that it only does 6Hz at short pulse lengths and as low as 1,5Hz at 50ms. So cutting would probably be slow.

[Twospoons]

Might be interesting to try replacing the flashlamp with an 808nm diode pump. Depending on the cooling setup on the NdYAG rod you might be able to get a bit more power out.  Bit of a project though.

[Mads Barnkob]

It is unfortunately one of those very special purpose pieces of equipment that has little to none hobby use. Its kind of for the same reason that I have a fully working digitizer xray image scanner sitting in the garage. It works, it was expensive, its full of wonderful parts, but it has no purpose.

I think there are 3 paths:
1: Take it apart, make videos about it, get nice parts
2: Save it for trading for something useful, when that someone looking for a "funny project" will buy into it. This will take years to decades
3: Save it long enough, because its valuable, that at some point you just throw it out or take it apart. Which is why, just go with 1 already!

I would love to see details and videos on this, even a non-destructive teardown with the goal to put it together again!