Different boot problem...

[DoN Nichols]

In article <12744 at helios.TAMU.EDU> n138ct at tamuts.tamu.edu (Brent Burton) writes:
>I just got my 7300 today.  It has an intermittant problem, but first the
>system:
>  7300, 2Meg Ram, no cards, WD2010 (no other fix, just the chip exchange)
>  and a 20Meg HD with "3.52jmC" operating system installed.

	What is "3.52jmC" ??  Where did you get it ???  What does it do
different ????

>The machine CAN work fine.  However, the problem is when it decides to work.
>
>The machine came to me diskless.  I had the 20Meg sitting around and so I
>installed it.  The machine came with the monitor and it's top case piece

	Is this the standard Miniscribe 20MB with the slow-boat-to-china
seek time?  If not, is it in the shielding can which came with the 7300?  If
it is, is it possible that the pressure of the grounding spring from the
center of the monitor pivot is pressing the can in such a way as to short
something?  If not in the can, is it possible that the grounding spring is
shorting something directly?

>separate from the body of the 7300.  To install the drive, I had to take it

	[...]

>My ideas:
>  * I ran the HD cables through those rectangular slots in the upper mother-
>    board RF shield.  Also, the power wire bundle for the HD was ran to the
>    back of the RF shield and up to the disk.  Is this the correct path of
>    the cables?

	The power cable should also come through the rectangular slot, if it
is coming from the motherboard.  If it is coming from the power supply, it
must have had a 3B1 power supply installed.  (Come to think of it, the 2MB
on mother board also sounds more like a 3B1) Does it have the extra hump in
the center of the top to clear a full-height drive?

	Another possibility is that you have too much stress on the power
cables because the hard disk or floppy are slid too far back in the range of
possible positions.  (This is usually more of a problem for the floppy.)  If
the drive is not the standard Miniscribe, the position of the power
connector may result in unusual stresses also.

	If the sheild can is canned, I also remove the grounding fingers
that touch the back of the shield can.  (They may be shorting something when
the case is in place.)  In the 3B1 that I have modified, they are held on
the modem-shield by pop-rivits, in the 7300, the connection was made by
melting the two together at the edges of the holes where the pop-rivits
would normally go.  In either case, they may be removed by careful drilling,
with a drill just a little bigger than the hole with the melted join, or a
little smaller with the pop-rivits.  DON'T do it in the machine!!!  And BE
SURE to use a vise to control all that sharp sheet metal.

	[...]

>One time when it was disassembled and didn't boot, I wiggled the AC wires
>from the power cable to the PS and the machine started up.  I wiggled them
>later on another no-boot and they had no effect (I really don't think they
>are a cause).

	You might check the voltages from the power supply during a no-boot
condition.

>What do the marching boxes mean and why doesn't it see the hard drive to start

	They mean that it can't find anything to read on either disk.  (If
the +12V is shorted, neither disk drive will spin -- but the monitor
shouldn't work either -- it is powered by the +12V.

	One other possibility is that the ribbon cable and connector to the
power supply is not making good contact when the side of the case presses
the bow of the cable inward.  (You might try pressing it in with your hand
while the system is open and powered up.)  If this makes a difference, you
might need to clean the connector pins with something like an eraser.
First, look for signs of overheating, which can point to a poor connection.

>loading?  I have two sets of disk cables and both sets result in intermittant
>boots.
>
>Does anyone have any ideas?  This is driving me crazy.
>
>Thanks in advance!

	Hope one of the things that I have mentioned helps!

	Good Luck
		DoN.
-- 
Donald Nichols (DoN.)		| Voice (Days):	(703) 664-1585
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