[time-nuts] Fluke monitor
GandalfG8 at aol.com
GandalfG8 at aol.com
Mon May 17 09:12:59 UTC 2010
In a message dated 17/05/2010 06:13:05 GMT Daylight Time, Leigh at WA5ZNU.org
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
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
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.
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