I¡¯m starting a new topic about the same 465B that I mentioned in Morris Odell¡¯s topic about his 7904 with interesting CRT distortion, because there is more wrong with my scope and I don¡¯t want to clutter Morris¡¯ thread with irrelevancies.
I¡¯m looking at the power supply rails (as thou shalt) and the main regulated rails (-8, +5, +15, +55, +110) look spot on in terms of voltage, but four out of five (all but the -8 V rail) have ripple that is way out of spec (0.5 V at 60 Hz). I also tried to check the unregulated rails, which are marked on the silk screen but do not have dedicated test points, so it¡¯s hard to know where to poke a meter lead. Regardless, I poked at each of the tree pads beneath each of the five large filter caps, and I got the following readings for the center pads (outer pads are ground unless otherwise noted):
-8 = +5 V (outer pads = -8 V)
+5 = +10 V
+15 = +24 V
+55 = +78 V
+110 = +162 V (outer pads = +78 V)
I do not understand what this means.
I had assumed that the ripple indicated bad bulk filter caps, but these unregulated voltages being so far off suggests much more serious malfunctions. Maybe the rectifiers are bad? But I would expect the regulated rails to be off if the unregulated were way off their specs.
As I said, I don¡¯t understand what I¡¯m seeing.
¡ª Jeff Dutky
