Failed detector, the light path, the filter, and the light selector? Please help

If it passed when you bought and first turned it on, it has to be fixable.  Follow stock troubleshooting routines- lamp (source) good, lenses clean, filters moving when/where they should.  I can see a blocked light path throwing all the errors you list.  iirc, the cover needs to be shut to ensure no stray light, so confirm that.

Find the service manual and don't be afraid to take the cover(s) off to see how the instrument is laid out.  You've got nothing to lose, if it has failed as you describe. 

Next level is board and detector level, so unless you find a tech of a certain age who remembers these units, you'll buy another one and swap things out until you get one working.  Play around with your unit first.  Buy some used lamps to see if lamp changing helps.

Good luck,  units of this vintage are quite straightforward and robust, and you have experience of it working, so that's to your favor.

All of the errors you listed could be due to the visible lamp not having enough energy output to the detector.  The ONLY lamp that is part of the startup sequence is the visible lamp and when they get old that is usually what causes the problems you listed.  Beyond insuring that you have no cells, empty or not, in the light path then that will usually be the cause.  Remore the cover, and then carefully remove the visible lamp holder.  If the lamp has black marks inside of the envelope then that will be the indication that a new lamp is in order. Of cource, an extremely dirty filter wheel and other optical components can cause these kind of problems and there is a right and a wrong way to clean the optics, especially the wavelength mirror.  Not only that, the installation instructions in the owner's manual for the visible lamp are sorely lacking so if you find out that it is indeed the visible lamp, get back to me and I will guide you through the visible lamp alignment and do NOT buy used lamps.  There is absolutely no way to know in advance whether or not they are even any good as to light output.  And yes, you can buy similare bulbs but the bulbs that Beckman Coulter used in the DU600/800 series specs were specially made to NOT have the UV filtering coating on them so they will not work correctly acrosss the entire operating spectrum for the unit.

Don Klees

Thank you, Don and LabWrench219569111123,

I am sorry I took this long to reply. I really appreciate the advice you have given to me and will try to fix the UV Spec. I was able to get a refund for it not working - but they said I could keep the machine bc it costs a lot to ship. Since the deadline for my research project was fast approaching a resorted to buying a vis spec from amazon and using a dye as a surrogate for the drug I would have been measuring (benzocaine lambda max 292 nm). When I have some free time I will look into fixing the machine, as you said, since it doesn't work I have nothing to lose. Thank you so much for the help!

Regards,

Shayl