ALC68 & PSU help please - Mod for variable power?

[smogthemog]

Hi people.

I was wondering if anyone could help me in my quest to add variable power to my ALC68 PSU?
It currently runs at 18-19A tube current and it's fixed at that. I have added photo's of the two cards in the PSU in the hope that someone will know if there is a mod that can be done to enable me to vary the power up and down around this fixed 19A setting?

I also require a replacement on/off switch for the front of the PSU as mine is broken, if anyone has one?

I intend on doing a full recondition of this laser as I did with my last one here: http://www.photonlexicon.com/forums/...ighlight=alc68

Any help appreciated.
Thanks
Jim

[tonyaztec]

PMed you sir, Happy new Year.

[mixedgas]

PMed You Sir...

Steve

[smogthemog]

Thank you both for your PM's, very helpful indeed.

I have looked a bit harder at the logic card and have found what seem to be two, a course and fine?, power control pots??? I have run it up to 30A and it's as bright as hell! I haven't got a meter but guessing well over a Watt going on the skin burn test Currently running at 25A and it's running quite cool too. Looks like the tube is OK.

[robotarmy]

Sweet! Another one!! I was going to try building a full power supply for these things, switch mode, plug in adapter for my two ALC68 heads. I'll let you know if that ever happens!

[mixedgas]

See attached schematic .

S#!t, Still cant get attachments to work. Smog , PM me with a email that can take a few BIG png files.

One pot is the PWM max width, the other is the gain, aka max power. Not supposed to mess with the one, as it can kill your passbank when the simple op-amp PWM generator latches up.

Steve

[smogthemog]

PM sent back Steve, thanks for that, appreciated.
I will have to identify which one is the one not to touch. I found, upon removal of the PB, each TO3 transistor has been fitted with a fuse I guess to protect it?
Photo attached of the fuses plus two others of where I am at with the strip down.

[mixedgas]

Ok, you have the one where in its factory state, turning on the opto-coupler using the 9 pin on the back greatly increased the current. I'll try to dig up what I have left. Piling system, once again.

Yeah, the fuze is there because they fail C->E shorted.

Were there a bunch of .1 ohm gold colored aluminum cased resistors, in parallel, near the front panel?

Steve

[smogthemog]

I have some drawings that Tony sent me about fitting a 100K pot around the opto isolator area, if these are the ones you are refering to Steve then I think??? I may be able to work something out from those. I will endeavour to look into it.
There where no bank of gold resistors. I have attached a couple of pics of the PB as it is now.

[mixedgas]

What does the front panel look like? What does the driver card look like? I can see the control card. There should be another card that drives the PB.
I'm pretty sure I sent Tony the mod or he sent it to me. Bruce also sent me the mod.

Steve