Tempest board problems

Yesterday was a nice cold, snowy day - so I stayed inside and worked on a
few Tempest boardsets. Got 2 outta 4 sets working - but the following are
giving me fits, so I thought I would see if anyone has some suggestions:

Both boards have had all the pre-requisite 'maintenance' done to them - all
socketed IC's cleaned and verifed as working in a good boardset, AUX board
tested and working, interconnect board working, interconnect pins
resoldered, etc. Also checked and verified the adjustment pots on the
vector section as good. Tested in a perfectly work cab with working
monitor, power supply, etc.....

Board one - plays blind but trips the spot killer when the monitor harness
is plugged in. All of the IC's in the vector section were replaced by a
previous owner. I verified all of the chips as working, and triple checked
the sockets. The voltages on the board at the test points look fine
(the -15V on the vector section is about -14.7, and the +15V is about
+15.2V). Any ideas?

Board two - plays (doesn't trip the spot killer), but all vectors are
trashed as shown in the following examples

www.enetis.net/~wandk/misc/tempest1.jpg
www.enetis.net/~wandk/misc/tempest2.jpg

First screen is the High Score Table and the second screen is the "Tempest"
logo. The monitor chatters like crazy - but only horizontal and diagonal
vectors are drawn. Putting the game into test mode only displays a few
random diagonal lines. Again, this board has had all but the LF13201's
socketed and replaced in the vector section. I again verified the IC's and
the sockets as good. I have spoken to 4 other people who have boardsets
that exhibit the same problems - so it must be a fairly 'common' failure.
Any ideas? Could it be a failing ram (I get no beeps in test mode)?

Thanks for any help or suggestions.

Walt

---------------------------------------------------------------------------
** To UNSUBSCRIBE from vectorlist, send a message with "UNSUBSCRIBE" in the
** message body to vectorlist-request@synthcom.com. Please direct other
** questions, comments, or problems to neil@synthcom.com.
Received on Mon Feb 26 13:26:03 2001