On Wed, 7 Mar 2012 15:26:07 -0000, "Arfa Daily"
wrote:



"Jon Elson" wrote in message
m...
wrote:

The problem with the amp is that
it will not work until it's warm enough. So some device or devices
must be a minimum temperature before the amp will work.

Very likely there is a bad connection, either a solder joint on a
component or a connector. Look over all the solder joints and
see if you can find one that is cracked. You may need to use a jeweler's
loupe or other magnifier to find it. It would be best to find this by
inspection, but if you can't, you can try to find it by applying force to
the board while running. (Of course, watch out for the high voltages!)

Otherwise, if there are plug-in boards or modules, check the connectors
there for dirt or corrosion.

It obviously is not a totally failed component or it wouldn't work
at all. While it is possible there is a temperature-sensitive component,
that kind of thing is fairly rare, and usually they fail when hot, not
cold.

Jon



That, however, is not the case for electrolytics. They fail more regularly
than any other component in modern electronics, and a failure to operate
correctly when cold is a very common thing with them. If that was the
problem with the OP's board, an ESR meter would almost certainly find the
offender in very short order on a cold board.

Otherwise, I concur with everyone else that a bad joint is the next most
likely failure area, followed by any semiconductor on the board. It is
normally fairly easy to find such problems with the help of a hairdryer, a
can of freezer spray, and a little bit of cardboard to confine where the
freezer gets to.

As to the tops being ground off the semis, this used to be very common a few
years ago. It often indicates that the devices used are actually very cheap
and common types, and that they just don't want you to know this, ensuring
that defective boards are returned to them for repair. An experienced
service person can often work backwards to determine what a device is, by
reverse engineering the area of board that the IC or whatever is located in,
and checking waveforms and voltages on its pins.

Arfa
Thanks everyone for the replies so far. I will post a picture in the
metalworking.com dropbox later today. I think I'll try replacing any
electrolytics first and then try the solder joint thing. I did talk to
another Fadal owner who has these servo amps in his mills and they
exhibit the same behavior. He has been using these machines over 40
hours a week for at least a couple of years by using a hair dryer to
warm the boards in the morning. Once warmed this way the machines will
run fine all day.
Eric