I have an HP 6200C flatbed scanner. Has anyone tried to by-pass the internal light source and illuminate transparencies from behind. Other than installing an on/off switch on the lamp, will this require modification of a heat sensor for the lamp? If so, what is the value of the resistor?

I intend to replace the cheap plastic scanning surface with true optical glass for print scanning. I am also considering cutting a hole in the original plastic surface to scan through for transparencies (nothing in the path of the imaging head). Of course this will only help if I can modify this P.O.S. into a decent transparency scanner.

Has anyone tried these modifications?

-- Michael Parrish (parrish@idworld.net), June 07, 1999

Answers

A couple of quick thoughts from a fellow tinkerer:

1. Before you interrupt the light source and bypass a sensor, perhaps you should see if a transparency adaptor is available or if the unit was designed to work with one.(relax, I'm not saying you should BUY IT! :-) ) My scanner has a port built-in, apparently to connect a moving light source transparency adaptor. There may already be an enable bit in a port to let you kill the light, bypass the sensor, do both, or to even connect your new unit's stuff in their place. Beats having to modify the old circuitry. :-)

2. Don't just cut a hole in the plastic! Yet... Different materials have differing indeces of refraction. The material you use to replace it could give some odd results. Especially, if the surface over the sensor is matched to counter refraction through the top surface. I'm not saying they do this for sure, but it wouldn't hurt to check it out first. Perhaps, just to be safe, you should try it without the plastic and with another material before just cutting a section out to see if there's any distortion in the output file.

Have fun, and let me know if you find a reasonably cheap way to make a high quality evenly diffused light source. I was thinking about rolling one of my own someday, too. I got about as far as thinking about frosted glass or perhaps using a light table/slide illuminiator, but got onto other projects since I didn't have a big need for it.

Good Luck.

-- Gerald M. Payne (gmp@francorp.francomm.com), June 08, 1999.

There is indeed a "slide adaptor" which originally came with the 6250c model of this scanner. You can buy it from HP and it'll work just fine on the 6200c. Go look on their website. It's really a pretty nice scanner.

-- Fred E. (feinstei@ford.com), January 03, 2004.