HP 2748B bulb replacement

On Monday (10/26/2009 at 11:49AM +0100), Philipp Hachtmann wrote: Hi Philipp, My apologies for not telling the whole story. I used the JKL model #7153 to replace the lamps in the HP2748B. There are 10 lamps in series in that unit and a pot that adjusts the brightness of all of them together. There's approx 50V across all ten, so each bulb should see about 5V across it. One of the lamps is used as a reference and does not shine across the tape. Nine of them do though, eight are data holes and one is the feed hole. The #7153 bulbs were US $0.75 each so I bought 20 of them as a life-time supply. There is a small PCB inside the head of the 2748B which these 10 bulbs are soldered to. It's a bit tricky to align the bulbs with the holes in the head once you have removed this PCB but I had luck poking and pushing them with a small screwdriver until each one dropped into place. I haven't finished my microcontroller interface to the 2748B yet but the tests in the service manual indicate that the replaced bulbs are doing the job nicely. Chris -- Chris Elmquist