|completely O.T. re: export only|
Message #9 Posted by Ellis Easley on 3 May 2003, 6:32 a.m.,
in response to message #8 by Vieira, Luiz C. (Brazil)
Except to say that I got a very nice 12C made in Brazil on Ebay, $15.99 BIN.
But back off the topic, years ago I heard about the BBC computer but I never saw one here in the U.S. Last year I got one on Ebay from Australia. When I went looking for info on the web, I found quite a bit - most of the manuals had been scanned and OCR'd (except for the drawings which were included as .jpg files), not that they were that big. One thing I found was very interesting: a scan of an ad from the early 1980's offering for sale, in England, BBC computers (the original one, either the A or B version) that had been made for export to the U.S. where they didn't sell, so they were brought back to England and converted to the UK version. This would have involved at least changing the video chip to PAL from NTSC and changing the power supply from 110 to 220 - this wouldn't actually be a big problem by itself, my unit had an Astec power supply configured for 220 which just didn't have the jumper option installed to switch between 110 and 220, so all I had to do was add a wire. Most line operated switching power supplies run on about 400V DC and are built with a bridge rectifier and two 250V electrolytic capacitors in series, with ~100K resistors across each one to equalize the voltage and serve as bleeders. It only takes moving one of the AC line leads from the "corner" of the bridge to the node between the two capacitors to convert it to a voltage doubler so you can operate it on 110V. The 110V power supplies in the BBC computers were probably dual voltage units jumpered for 110, so they would just have had to open up the power supply chassis and move the jumper. However, if the safety rules in the UK are like the US, doing that modification would require the unit to be safety tested again (HiPot ground continuity/insulation leakage test or similar).
A couple of us got good deals on samples of 220V Tandy video monitors once. Converting them to 110 was a bit of a pain because they had a single electrolytic capacitor so I had to find a way to mount two capacitors and add two bleeder resistors.