On Wed, Jul 29, 2009 at 10:08 AM, Philip Lord<firstname.lastname@example.org> wrote: > Thanks guys, You bet. > It's going to take me a little time to go through all this stuff. I did > however have a few moments to quickly check the voltages across pins 1 & 4 > and 5 & 4 of the J8 power connector (disconnected from motherboard)...they > both read about 8.2V AC, which unfortunately isn't 12V as Ruud mentioned. I don't have a static PET to check (anymore), but 8.2VAC is at least close. The critical thing is that the 7805 needs some "headroom" for it to properly regulate. ISTR that 7.5VDC is close to the minimum input voltage for a true 7805 to work (there are plenty of "low dropout" regulators now that will work with the input under 6VDC). Check the input DC to the regulators with the board plugged into the PSU (well... the transformer and filter cap ;-) and check that against the datasheet for the 7805 if it happens to be below 8VDC. You could be experiencing a problem with the rectifier (the diodes between the transformer and the 7805s) or the harness connector (I've seen some charred ones in the past from too much resistance leading to too much heat, etc). > I'll update you both (and the list) once I have had more time for testing, > starting with the 7805's Sure. With problems like this, check all your power and work backwards. At some point, the outputs and the inputs won't match and your fault is between the two. -ethan Message was sent through the cbm-hackers mailing listReceived on 2009-07-29 23:58:51
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