mesa component wrong spec?

[Alex R]

Here's a funny thing. On the attached Mesa 50/50 psu schematic I've circled two labels. Sorry about the quality. The top one says there's 436v at C with the power level switch in the HI position; the lower one rates the cap which sees that voltage and goes to earth at 400v. I've just had in a while-u-wait job on one of these rack stereo power amps, which was blowing fuses whenever the switch was in the HI position, and eventually traced the fault to C19, which was closed in a dead short. It's an orange drop rated at 400v all right, and the voltage at C was 440.

Design fault? Or am I missing something?

[Rick Erickson]

Amazing isn't it? I've seen other "design flaws" like this on a schematic where the specified voltage drop across a resistor is enough to cook the resistor. These kinds of errors aren't specific to any one manufacturer either. It just proves the old statement - "Never Assume Anything". I would put a .1uF 600V or better cap there.

RE