In a message dated 17/05/2010 06:13:05 GMT Daylight Time, [email protected] writes:
You're right about the current. I just checked it with my DMM and got 45ma. My inline power meter must not be that it's not that accurate at the low end. The display works; the backlight works; the processor must be doing something since it prints a variety of messages. It's the RS232 that has flakey. The hardest thing at this point is to unsolder the 16-pin header. Bob suggests that a 12v regulator may have failed. ------------------ That's encouraging re the current, I'm also inclined to the view that it's likely to be an RS232 issue but still wouldn't rule out a quality issue without careful checking. I'm not sure what Bob means when he suggests a 12v regulator may have died as there isn't one fitted to this unit. The only regulator is the surface mount 5v unit which, from the measured current, I would say is working correctly but that's easy enough to check anyway. Unsoldering such a header can be very difficult if you try to do it a pin at a time, especially on a plated through PCB. It is possible to clear one pin at a time with either a solder sucker or solder braid, or a combination of both. I've also succesfully removed connectors and IC sockets from double sided PCBs using a powered vacuum desoldering tool but it's generally less likely to cause damage if you can melt all the solder at once to separate the boards and then clean off the surplus after. There's a variety of ways to do this, from hot air guns to specially shaped iron tips, and as many opinions as to which might be the best method:-). I would prefer a shaped iron tip in this particular instance but they don't seem to be so widely available these days, at least not for the irons I use, so might also suggest flood filling along the pins with molten solder as another option. With this though you have to be very sure your iron has a big enough tip and that there's enough heat reserve in the system to ensure the whole lot doesn't solidify and leave you in a lot more mess than when you started. PCB damage to pads and through plating is again a risk with everything heated at once and practice on something non essential would be well advised. I still can't access my units right now and can't remember the exact physical setup but if the header pins are exposed and accessible between the two boards by far the best option is likely to be cutting them and sacrificing the header. That might seem drastic but headers are much easier to replace than circuit boards and all you need do then is remove each pin separately which, with care, greatly reduces the risk of damage. If there's a plastic moulding at one or other end of the header which still seems to be locking the pins together these are fairly easy to remove, softening with a nearby soldering iron should generally release any that seem well locked in place or a thin scalpel blade can be used to carefully cut through the plastic and separate the pins that way. Emphasis though on "thin" blade, thicker blades such as those found in a Stanley knife can act as a wedge and force the pins apart which again carries risk of damage when close to the PCB. regards Nigel GM8PZR _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
