Switcher PS temperature...

Bill> It's rated for 8 amps with no significant airflow (if I Bill> understand the specs correctly) so, I'm not even pushing it to Bill> its limit. Anyway, after about 10 minutes of operation with Bill> the case open and the new PS sitting off to one side (clear all Bill> around), the two heat sinks are too hot to touch. Is that Bill> normal operation for this kind of supply? No. It makes sense for power supplies to get very noticeably warm at their design load, because they are optimized for that load, and it is quite acceptable for various parts (like the transformers) to heat up by 10 or 20 degrees at load. But if a heat sink is too hot to touch, that means the transistors mounted on it are quite a lot hotter yet, which means they won't last long. One possibility is that the original design was correct for the stated load, and then it was hacked up by butchers who wanted to trim down the cost and didn't care that it invalidated the original design. Apparently this happens. It was documented at length in a recent article in either QST or QEX (U.S. amateur radio publications), in which the author took one of those butchered supplies, reversed the butchery, and redid some parts to make it a general purpose bench supply. It's an excellent article, very well written if you want to understand better how those supplies work. paul