Hi,
yeah I know you shouldn't resurrect the dead, but I'm doing my Master Thesis right now and there may be some months between a good evening of scope repair (and thus me posting new stuff here), so bear with me.
I just opened the scope and poked around on the PSU rails, which can be measured on the Z-Axis board as described in this PDF:
http://w140.com/Tek_7904_Power_Supply.pdf.While they seem fine voltage-wise, their resistance is a bit low (5-10%) on some rails, and incredibly high (2,8kOhm instead of 250Ohm) on -50V rail.
I was quite baffeled and went on a hunt for an early (i.e. low serial number) service manual, but I can only find the higher one (Tagged B260000-UP on Title page and top page corners).
Does anyone have a low-serial manual, so that I can actually check against what MY scope should do, instead of a ten-year-later model?
Quoting David here, in the hope he has one (does quoting give you a notification?).
Thanks,
Andreas
Some of the later plug-ins drew more power and the 7904 was marginal in powering them.
I have not seen any documentation on the late 7904 fan. My guess is that it is similar to the fan in the 7844 which also uses a one piece chassis and there is plenty of space at the top/right/back of the 7904 chassis to add a tubeaxial fan exhausting to the rear. The 7834 uses a two piece chassis and its fan exhausts to the right.
Note that there separate 7904 service manuals for early (serial number B259999 and lower) and late (serial number B260000 and higher) model 7904s and the 7904 with fan was on even later. My late model manual does not mention or show the fan.
EDIT: sleep-deprived brain shut off during typing.