On Mon, 2010-03-01 at 17:00 -0500, Timothy Normand Miller wrote: > Any suggestions and help would be most appreciated!
Just as a reference.. I presume you have the user manual for the board. It mentions the power supply stages, and shows a diagram.. 5V in -> 3.3V -> 1.5V core voltage, via 2 LDO regulators (the LM1085 chips on the board). Looking up their pin-outs, noting pin 1 is the one with the dot next to it.. you should have: 1: Adj/Ground (Might connect to GND, might be a divided version of the output. 2: Output (also connected to the metal tab at the back) 3: Input. One regulator ought to show 5V in, 3.3V out, the other should be 3.3V in, 5V out. Certainly change out the damaged components first. The tantalum capacitor might have blown due to over-volts - or reverse polarity. (Was that what happned?) The diode might be the suggested reverse input -> output connection diode for the regulator - OR, be a reversed protection diode to short the input in case it is the wrong polarity - OR, a series pass diode for the input. (Or none of the above). I would suggest initial power-up via a current limited lab PSU. Don't set it too low though, or the board won't boot. I's suggest trying at 0.5A to start with, giving it up to 1A as it wants.. That ought to help prevent further collateral damage if the regulators are blown. Having just thought of this.. ramp up the voltage slowly.. these are LDO regulators, not switchers - so you "ought" to be able to persuade them to come up slowly. At 2 or 3V input, the 1.5V output "might" just start to regulate, make sure it doesn't exceed 1.5V. Similarly - watch the 3.3V output, and make sure it doesn't rise above 3.35, 3.4 (say), as you power up. In any case - if there was damage to be done, it has probably already been done - so you're unlikely to screw things up further. You might even try powering up without the diode - perhaps even without the capacitor - or solder a similar value capacitor in its place for testing. Best wishes, -- Peter Clifton Electrical Engineering Division, Engineering Department, University of Cambridge, 9, JJ Thomson Avenue, Cambridge CB3 0FA Tel: +44 (0)7729 980173 - (No signal in the lab!) _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
