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Helium Cadmium Laser Help (Omnichrome series 74)

Blue Flash Dave

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Joined
Jun 29, 2022
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4
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The helium heater should come on very rarely. It only comes on if the He pressure is low.

The Cd heater will be on every startup as it must vaporize the solid cadmium metal on every run.

How long are you running it for? A HeCd takes 10-15 minutes to heat up and start lasing once you set it to run.

Are you sure it's the UV model? What's the full model number? I'll see if I can dig out the list of models from when I had one.

What are you terminating the beam on? The UV emitted by a HeCd will make many things fluoresce a very brightly, plain white paper for example fluoresces nrightly with quite a deep blue colour. Terminating the beam on a piece of metal should produce no fluorescence.

What colour does the tube glow on startup and once it has been running for 15 minutes?
Hello ! I've finally found people who appear to know all about Omnichrome series 74. I dont suppose you have the circuit diagram for the head : only I cannot get the head to lase. It appears to try to start but the LC controller stops after 15 seconds and shuts it down. The error code is not specific.
I am a bit suspicious about the head PCB - there appears to be a missing component, possibly a relay, called 'K2'. Here are some photos - would you be able to help ? The head is in pristine condition physically...
 

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Eidetical

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May 14, 2022
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201
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I think you are the sole active member with any functioning HeCd now. Rub it in why don't you... :crackup:

Good information, some of which I forgot in my original post. Been a long time since I had a HeCd. :yabbem:
Not anymore! There's a new He-Cd in town, and it's single mode too. For holography with Covestro's photopolymer materials, I needed a laser with as much power as possible, but diode-based lasers of acceptable quality are hard to find used and were very expensive with long lead times for new to get a wavelength smaller than 450nm but not into the UV. Good thing this Kimmon system with very low hours and known history was available.

Kimmon in Lab.jpg
 

Blue Flash Dave

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Joined
Jun 29, 2022
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4
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Hello ! I've finally found people who appear to know all about Omnichrome series 74. I dont suppose you have the circuit diagram for the head : only I cannot get the head to lase. The LC controller starts the sequence, the heater glows, the fan turns on and everything seems OK. But then after 15 seconds the LC shuts down. The error code on the RS232 port is not specific (nor is the LED flashing six time on the controller).
I am a bit suspicious about the head PCB - there appears to be a missing component, possibly a relay, called 'K2'. There are voltages present on the contacts in this socket.
Here are some photos - would you be able to help ? The head is in pristine condition physically...
 

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Joined
Mar 10, 2013
Messages
2,918
Points
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Not anymore! There's a new He-Cd in town, and it's single mode too. For holography with Covestro's photopolymer materials, I needed a laser with as much power as possible, but diode-based lasers of acceptable quality are hard to find used and were very expensive with long lead times for new to get a wavelength smaller than 450nm but not into the UV. Good thing this Kimmon system with very low hours and known history was available.
Nice. I've always wanted a big one like that. they're glorious :D

Hello ! I've finally found people who appear to know all about Omnichrome series 74. I dont suppose you have the circuit diagram for the head : only I cannot get the head to lase. The LC controller starts the sequence, the heater glows, the fan turns on and everything seems OK. But then after 15 seconds the LC shuts down. The error code on the RS232 port is not specific (nor is the LED flashing six time on the controller).
I am a bit suspicious about the head PCB - there appears to be a missing component, possibly a relay, called 'K2'. There are voltages present on the contacts in this socket.
Here are some photos - would you be able to help ? The head is in pristine condition physically...
I would have to find out what the 6 blink code is. It sounds like no tube current, which would be a power supply regulation issue. but Idk for sure. if you have the software or remote it will tell you in english.

and it's normal for K2 to be unpopulated. They're all like that.
 

Blue Flash Dave

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Jun 29, 2022
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Nice. I've always wanted a big one like that. they're glorious :D


I would have to find out what the 6 blink code is. It sounds like no tube current, which would be a power supply regulation issue. but Idk for sure. if you have the software or remote it will tell you in english.

and it's normal for K2 to be unpopulated. They're all like that.
Thanks UK : it's good to know that K2 should be empty !
The 6 blink code on the LC500 is simply described as "Laser Head Read Error". Reading the manual, I cannot see any reference to a specific 'read' event - and interpret this as being the LC500 'looking' for a particular voltage on one of the pins; but I do not know which one.

I have also checked continuity on the cable (see the writing on the photo) and there are descrepancies between the actual cable and the designation in the manual (page 41) - but the voltages on the external test sockets are within the tolerances stated in the manual (page 29). Unfortunately, in the troubleshooting section, the test sequence involves 'going to paragraph 6': but there is no paragraph 6.

I'm a bit annoyed with Melles Griot for not providing any support. I've left eight messages witrh their technical team in the US over the last month and heard absolutely nothing from them.

Cheers, Dave
 
Joined
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Melles Griot doesn’t really exist anymore. They were bought out by IDEX a long time ago. They haven’t supported lasers in a long time they mostly only make optics now. As for your error code I’ll take a look into it and see what I can find out and get back to you. I actually have this exact laser head, so i can make comparisons.

Edit: also, that universal laser controller manual is actually for a different unit it is not for the helium cadmium lasers by the way.
 
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Blue Flash Dave

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Jun 29, 2022
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Ahhh...that would explain the cables ! The manual was shipped with the LC500 and, stupidly, I never occurred to me that it wasn't the right one. So - I think to myself 'are the cables correct for the Head - they too were shipped with the LC500' ?!
I'm glad to hear you have a Series 74 : In English terms it is the 'dogs bollocks' i.e. it looks absolutely superb. Many thanks for taking time out to check out errors.

Catch you later...
 
Joined
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Messages
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I don’t see anything obvious in the manual about six blinks. Unfortunately I don’t have a lot of context for what the error entails. Can you disconnect the rs-232 and describe to me exactly what happens after you push the start button? As much detail as you can give me.
 





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