Hello,

I recently picked up an old Spectra Physics 120 HeNe laser head plus 256 Exciter, and I'm not getting any laser output. However, the tube glow looks to be around the right sort of colour and I don't think there is air leakage..

I've yet to try cleaning the optics, but I have checked the tube voltage and current and I'm not sure if I have a problem here, as it's 2.7kV and 6mA, whereas Sam's Laser FAQ suggests it should be 3.7kV and 7mA. Also, after being powered up for a while the power supply seems to drop out -- I get a buzzing sound and the plasma goes intermittent, before stopping altogether. When it's intermittent the tube voltage spikes up to around 4-5kV (at least that's what I see it jump to on my DMM). So, perhaps a PSU component is on its way out?

I'd be grateful of any suggestions that folks may have. I'm hoping it's simply a case of resistor or cap that has not aged well.

Cheers,

Andrew