UnixPC hardware problems (help requested)

[Roger Florkowski]

I have a problem with my 3b1 that only happens when I first turn it on.
The problem is that I only get a screen full of horizontal bars.
The only way I can get the machine going is to give it a 'jump start'.
I have to turn it off, thump it on the table, and turn it back on
again.  This happens everytime the machine has been physically turned
off.

History
-------
My machine is a 3b1, 2 Meg ram, 67 meg Miniscribe. 

The first motherboard died.  I had it fixed by AT&T in CA.
The power supply died.  I had it fixed by AT&T in CA.

The second motherboard had a problem where the machine would just
lock-up and stop.  No error messages.  Nothing in /usr/adm.  The
screen was frozen with the last thing that it was doing.  If I hit
reset (or turned it off, and back on), I would get the all too familiar
horizontal bars.  The machine would not come up unless I thumped
it on the table.  This whole scene finally got up to a frequency of
5 crashes per day.

I replaced motherboard #2 with one from another "known-working" 3b1.
This motherboard (now we are on number 3), was also repaired once
by AT&T while it was in it's previous 3b1 body.  This motherboard
worked great for about 4 months.  It didn't crash, and I had
no problem turning the machine on and off.  Now I canno longer successfully
turn the on and off.  I get the horizontal bars every time I turn it on. 

Help!!??
--------
I'm stumped.  I've looked at the inside of this machine so many times
I can almost rattle off part numbers from memory.  Does anyone have
any suggestions?  It sounds like I have a bad connection (since I have
to bang the machine to get it started).  

-- 
Roger Florkowski	       		{uunet!uvm-gen, attmail}!banzai!roger
The People's Computer Company			  `Revolutionary Programming'