VAXstation/MicroVAX 2000 CPU/FPU overheating?

A good idea, but I don't think this is the case. According to the technical manual, the power supply and fan should be the same in the main system cabinet and in the matching expansion boxes (same chassis) - I have two expansion boxes (tape and disk) and all three have exactly the same fan installed. I've not done measurements, however the fan seems to be operating correctly, good airflow, doesn't sound like it's dragging etc. The sound and airflow are not noticibly different from the other two boxes. According to the technical manual, the fan is supposed to be "variable speed". It's a 12V DC fan, however it is powered via a 7905 (-5V) regulator which has it's reference through a resistor divider which includes a thermistor. So presumably it speeds up as the cabinet gets hot - since the thermistor is in the power supply, which has somewhat of a separate airflow path (metal plate between PS and boards) it may not detect the "hot spot" forming at in the other airflow path. I'll have to do some measurements. I could try hard-wiring the fan to full power, however this thing *should* work as it is designed, and the fan supply seems to be working, as noted above, it behaves virtually identically to the other two boxes. I've done some googling and have not found any refernces to other uVAX2000's having this problem. Removing the color display buffer board should allow for better cooling of the mainboard, as the two boards are large and sandwiched together in a fairly thin air duct. But again, I think if this were a common cause of this problem, there would be references. The fan in mine (as well as the two expansion boxes) is a: PANAFLO Model FBP-08B12H made by Matsushita I didn't have to take any of my boxes apart, the fan label can be easily read through the rear air grill. I would like to know if your machine gets as hot as mine - with the main cover removed and nothing else, after a few minites, mine gets a very noticable "hot spot" on the flexible shield covering the upper (solder) of the mainboard above the CPU's (near the front of the machine, near the center but more on the drive side). Unfortunately you can't access the CPU/FPU heat sinks without removing the board (unless you have a thin temperature probe) ... on mine, both the CPU and FPU sinks get to the point where hanging on to them would probably result in skin damage (blister etc.) - it seems to me that the FPU (the one closest to the RAM array) get a bit hotter, but both are well into the "uncomfortable hot" range... Given that they both seem to run directly from the 5V rail, and that is well with spec (something like 5.01 when I measured) I can't think of any external problem that would result in that much current draw and sill have the machine appear to operate normally (can't really think of an internal problem either). Really has me stumped - there seems to be reasonable airflow through the cabinet, nothing seems to be blocked etc. It just gets so hot it dies... if the system were that "close to the edge", I'm sure I would have seen references to more problems. I did find a few references to thermal death when operated in very hot environments, but I keep my office on the coolish side. Dave -- dave06a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.classiccmp.org/dunfield/index.html