gill (10/08/82)
#N:physics:15700001:000:1779 physics!gill Aug 28 00:23:00 1982 Every 212 I have seen in a metal box gets very hot. The transformers haven't. A filter capacitor may be defective causing the 212's bridge rectifiers and transformer to overheat (the line from transformer to 212 is center tapped AC (about 24V, from what I remember)). I can't think of any other part being defective that would allow the modem to still operate. Why do 212's run so hot? It seems WE doesn't believe in convection cooling. The boxes are totally sealed, so any heat generated must first pass through the air in the box, then through the case. This may be why 212's in a box are less reliable than the ones in racks. The boxes were designed for the much simpler 300 baud modems. The larger synchronous modems have air slots and/or fans in the rear. Is your modem running too hot? If it works, and the circuit board isn't turning brown; probably not. WE components are made to withstand pretty rough temperatures and their transformers are a far cry from the type's you get in TI calculators (its a shame they made them so large that they take up two AC sockets, but you can't win them all ...). The "too hot when too hot to touch" rule isn't really valid. Anyone who's brushed up against a 7805 regulator going full tilt (a very common part in home computers) will tell you its quite happy at searing temperatures. My 212's have never gotton to hot to touch (the case that is). In any case (ho ho), you probably don't have to take out fire insurance; the box is probably well sealed enough that any combustion will run out of oxygen. It'll probably still work in 35 years ... Gill Pratt ...alice!gill OR gill@mc p.s. Don't treat your 212's like your phone. It's much more sensitive to vibration. The crystal oscillator DIP is the first thing to break.