http://www.hiarcs.net/forums/viewtopic.php?t=4871
I just took delivery of a Fidelity Mach III Master 2265 (model 6113) and was rather shocked to find out that it has no game memory. When you turn off the unit, your game is gone. There is a workaround, albeit tedious, by using the Problem/Position option. However, I often play slow games -broken up by other daily activities- and it means that I'll need to leave the unit on for several hours which makes battery use problematic.
Problem is, the unit didn't come with an AC adaptor and since this is a rather 'precious' (for me anyway) & expensive unit, I wasn't about to take chances blindly trying adaptors from my rather copious stock...
There is less than optimal information about voltage/amperage and almost no information on the internet about the correct polarity for various chess computers.But, by coincidence, a day or two after the 2265 arrived, I happened on a Fidelity Designer Display 2000 for sale for $12 (!) with adaptor included and after a 4 hour drive to pick it up, I hooked up the unit and it worked fine with the adaptor which has a positive (+) tip polarity. (I decided to do all my AC adaptor testing with the 2000 and then apply the results to the 2265). However, it turned out that the adaptor for the 2000 was one the seller had just found around the house and the voltage was 15v, 1000ma. Yikes! Anyway, there was a slip of paper in the 2265 box that said a 300mA adaptor with a selectable voltage was enclosed (it wasn't as it turned out) and that the user should set it at 7.5v which seems right as far as voltage is concerned.
So, the only thing to verify was the polarity. As noted above, the 2000 worked with a + tip polarity, but I didn't want to depend on that since some circuits apparently will allow for reversed polarity even though only one is preferred. I opened the back of the 2000 and, sure enough, the negative (-) battery terminal was connected to the outside of the jack so the tip had to be positive (+).
So, case closed (at least for me- everyone reading this takes their own chances
): The Fidelity Designer series will work with an adaptor that has 7.5-9.0v at 300mA and a positive (+) tip polarity. I happened to have one and both the 2000 and 2265 work perfectly with it. I decided to check a number of my adaptors for tip polarity. Two of my Novags and a Radioshack use a negative (-) polarity. A Saitek (Chess Challenger) and Excalibur unit uses positive (+) polarity.If anybody else has other Chess Computer AC Adaptor information, particularly polarity, perhaps this thread would be a good place to put it. Personally, I don't like having to pay $25 (going price on one website) for an adaptor that I may already have, but there is very little information elsewhere on this subject.