Good Morning All,

Some of you may know as ive messaged you directly or were are the UK meet but I have kindly had a couple of ALC68 sets donated to me.

Both need repair but my main focus is currently on the pair with the EIL-4000 / Continental Laser PSU.

Im keen to get them both working to try and make sure we have some gas lasers for many years to come, I love the coherent light from gas lasers and with all the diode action now these beautiful lasers are slowing getting few and far between.

High res image of the PSU - here

The PSU had a shorted passbank (dead transistor(s)) and old / cracking caps, the PB has been repaired and ive got 2 new caps stuck at the post office currently.

Before repair it would lase straight away at "full power" (30a) due to the shorted PB, since repair when fired up the laser dosnt start, you dont hear the solenoid clicking on, it seems to be in some sort of standby mode now.

Now I assume this is back to correct operation as I wouldn't expect it to "just start", when I say just start we powered on > short delay > laser fired.

Ive asked a few people and read everything I can find on the internet (not always in english!) and have identified that there is analogue current control 0-5v via the DB9 connector on the back of the PSU, image here.

Here is what ive found out and believe to be correct thus far for the DB9 / remote connector :

Pin 1 - 0-5v analogue current control (+)
Pin 5 - 0-5v analogue current control (-)
Pin 6 - Volt meter point (+) which somehow relates to tube current
Pin 7 - Volt meter point (-) which somehow relates to tube current

The source for these mainly came from here but the 0-5v seems to tie up with random other forum posts online.

I've built the circuit as listed on his site (- the resistor as I want 0-5) which is tested and working.

My question now is, I believe there would be some form of interlock on this DB9 which would be required to get the PSU to start the head lasing, this is what im hoping somebody can confirm and let me know which pins on the DB9 need shorting / switch adding to them to give me "on / off" or "standby" control and would explain why there is no lasing after PB repair.

I assume in production there would be some sort of foot switch connected to the remote for a surgeon to use or some sort of on / off switch on said remote.

This has been sort of verified by a user catalanjo (hes waiting to get access to paperwork back home as hes away) and a guy is selling a couple of similar PSUs on ebay (here), you can see in one of his photos (here) there is a couple of wires connected on what looks like pins 3 + 4, may be a red herring but maybe someone can confirm.

Lots of high res pics of my set here that my be of use to you.

Any help much appreciated, thanks in advance.