Update:Bport CNC Series 1 BOSS Quill

First. Thanks to all whom have responded.
I swapped all of the SMP (axis control boards) several times but
the problem with the Z-szis still remained. So the boards were not
the problem.
On the large control cabinet heatsink I located another set of
transistors. You can not see the Collector case only the posts and
screws are visible. I used a digital multimeter in diode mode to
check the connections between posts. All readings were quite close
except for one set of posts.
659 and 480
670 and 500
002 and 000 <---
672 and 493
I located a text document on the 2000 retired files list on
http://metalworking.com/ There was a text file and 2 pictures of
the his problem and solution. The problem he identified was in
another axis and some of what he was describing seemed to fit my
problem. His pictures verified where I was having a problem.
To get access to the transistors you need to remove all 4 boards
at the bottom of the large heatsink of the control cabinet. There
are 3 metal stamped plates with about 12 wires coming off one side.
The wires are number and the plates are marked for what axis each
serves. There are 10 small sockethead capscrews holding the plate to
the heatsink. Once all the screws are removed you can access the
transistor to remove it.
The transistor type you are looking for is a 2N6547 (this is the
generic class naming scheme number). NTE make a replacement
transistor named NTE53. They are pricing out around $12 each on the
web.
The 3 SMP boards hold 4 transistors each and the 3 metal stamped
plates hold 4 each for a total of 24 transistors. Just be aware that
any of them can go without affecting the other transistors. From
what others have posted this seems to be a common occurance. The
problem for me was we have only had the machine for a little over a
month and had no historical background of potential problems. I
really appreciate groups and posting boards like this, they can save
money and time.

Once again thanks for all your time and help,
mc_n_g