My HeNe won't start.............. Help!

[John Sonley]

What am I talking about:

Laser: It's a Melles Griot 05-LHP-828 Manufactured in May 1999. Serial No. 3337DF-1 with a power output, when it worked, measured by Jem as 33mW

Power Supply (PSU): Melles Griot 05-LPL-944-080 Manufactured May 1999. Serial No. 3337DF-2 with an output stated as 4.4 - 5.3kV @ 8mA

I bought this laser new and have been using it regularly over the past couple of years to make H1 and H2 image plane holograms and it's worked fine. I made my last H2 yesterday with great results

On occasions when I've switched it on I've heard a few 'clicks' as the ignition pulse fired but failed to start the tube - but it always starts within about 5 - 10 secs. It started fine again this morning after about 5 - 10 'clicks' ............................ but this afternoon it did not start after about 30 secs of clicks and I've tried it many times more, without a firing

As my hobby holography lab is in the basement of the house where humidity is always high, I took the PSU and sat it on a radiator in the house to warm it up - no joy!, no change and no start!

I took a hair dryer to the laser and gently warmed it all over - no joy! no start

Clue to the problem: when switched on and the laser is trying to fire/ionise, there is a most noticable 'click' coming from the far end of the laser housing, very close to where the beam is emitted, it sounds like high voltage sparking and I'm wondering if some bit of insulation may have failed and the ignition pulse is being reduced to a voltage below the ignition voltage of the tube by internal arcing

The power supply seems lively - if I slowly pull out the white Alden connector while the laser is attempting to start there's sounds of fat and beefy sparks jumping in the recesses of the connector for about quarter to half an inch after the plug/ socket have separated

If anyone could help, with experience of these lasers I would be most obliged because I'm rather nervous about opening up the laser housing myself, without guidance - after all it cost nearly £4000 years ago and holography is my hobby

BRgds
John

[DZ]

Hi John, welcome to PL!

Is this a cylindrical head or rectangular? If it's cylindrical it's going to be a bit difficult to repair I suspect. If the latter, then it shouldn't be too much trouble to remove the top cover and inspect the ballast resistors as this is where I'd bet the problem is.

[John Sonley]

The steel metal framework of the laser is about 40 inches long and in cross section, the framework is about 3" X 3".
Looking through the top of the frame work I see the laser tube mount as about one and threequarter inches in diameter, black material - and about 40 inches long

If there's a mechanism for me to take a digital photo and send it as a .jpg then please let me know and I'd be able to do it very quickly
BRgds
John

[ElektroFreak]

In your user profile there is space for your picture albums. You can simply upload pics into your album and then copy and paste the [IMG] code that appears below each picture into your post.

[mixedgas]

In your user profile there is space for your picture albums. You can simply upload pics into your album and then copy and paste the [IMG] code that appears below each picture into your post.

Sounds like bad cable or bad ballast resistors. Melles usually pots their ballast resistors in a black silicon rubber. I agree with DZ, most likely ballast Rs.

Steve

[John Sonley]

I've uploaded a picture of my laser but I can't seem to find a way of copying it into a message
BRgds
John

[John Sonley]

At last I think I've found a way of copying a picture into this thread - my problem laser

[DZ]

Now that's a HeNe!

If you could, carefully, remove the top cover and inspect the balast resistors. Maybe get a couple pics of the inside and post them here, that would help quite a bit.

That top half of the cover should just lift right off after you remove a few screws.

[John Sonley]

There is no top cover. The rectangular case wraps around the central tubular laser housing and there is one screw on the vertical surffaces on each side at the front and back.
I would need to look underneath the laser to see if there is some type of fastening of the front and back plate as I don't think that the rectangular surround will slide off the internal tube housing the laser unless I remove one or other of the ends
Brgds
John

[John Sonley]

Where will the ballast resistor be - probably inside the tubular housing which also houses the glass laser.
What type of resistor is it? - Other sites say it will probably be 75Kohm but I wonder what wattage - from the PSU rating it suggests 5W.
I'm in the dark as to where to go from here
Brgds
John