Repair techniques ... I/O pins and power supplies

From: Michael Brutman <mbbrutman_at_chartermi.net>
Date: Tue Apr 24 20:37:14 2001

I've always wanted a PCjr with an expansion chassis on it, but
they were pretty expensive, and I got by without one. 15 years
later I have found one on Ebay and bought it, but alas it's not
a happy ending. There are at least two serious problems that I
need to fix.

The first problem is a broken I/O pin on the expansion bus
that comes off the motherboard. The pin is in a 60 pin
 rectangular connector, and spacing is tight. he broken pin
is a data line pin, so if I don't fix it, I can't add any
sidecars to the machine. How does one go about replacing
a pin? Is it possible? Or am I going to have to desolder the
connector and try to replace the entire connector? (And I'm
not good with a soldering iron ... I can't even tin wires.)

The second problem looks to be a bad power supply. The
expansion unit has it's own power supply because the PCjr power
supply is only about 33 watts. The expansion unit has extra
memory in it that is not being seen by the system unit; I
suspect that is because the +5 output on the power supply
is reading about 1.8 volts. (According to a digital
multimeter.) I measured this with everything connected,
so there certainly is enough load. (I don't think that
this is even a switching power supply, so the load issue
is moot.)

The power supply has a "pick" line that is
probably activated from the main unit, so that it doesn't
have to have an independent power switch. How does such
a pick line work? Is there a way to fool it on? What
does it use for a ground? (I didn't see one clearly
labeled that belonged to the pick line ... perhaps it
was the same ground as the +5v line?)

How can I confirm that this power supply is truly
toast? And it is, then how do I replace it? (I'm willing
to scab in a reasonable substitute - it probably can't be
a switching supply though because there won't be enough
load - it's probably only 512KB of chips on board.

The expansion unit is a Rapport if that helps anybody.



Thanks,
Mike
Received on Tue Apr 24 2001 - 20:37:14 BST