see below, plz.
Dick
----- Original Message -----
From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Wednesday, June 13, 2001 12:09 PM
Subject: Re: Ebay horror ...
> >
> > While it's probable you're right about your own relationship with your
> > computers, others seem to have different relationships. My own experience
> > suggests that if I replace the serial port board with a fully functional and
>
> If you know it's a fault on the serial port (for example), then you've
> done almost enough tests to determine what the fault really is. I am not
> talking about 'fault finding' that goes like : 'The modem doesn't work'
> 'Replace the serial card and see what happens' 'Oh, seems to be OK now'
> -- that's not fault-finding, that's why I object to board swapping.
>
Well, it certainly doesn't find the fault in the serial board, but it does find
and fix the fault in the computer. Since serial boards cost less than the 10
minutes it takes to swap them, and it costs 100x that much to fix the serial
board, at a minimum, it seems to make sense to swap the board. That does fix
the computer, doesn't it?
>
> And if you know where the fault really is, it doens't take that much
> longer to replace the fualty chip or whatever.
>
That's true if it's a serial board. However, if it's a mono video board, also
costing less than a half-hour's time, and replacing it gets the server back into
service, while tracking down and replacing the 100-pin fine-pitch pqfp that
costs 10x the retail cost of the new video board (don't ask me why, but it does)
and that only if you buy 100k of them, it's still cheaper and more sensible to
fix the computer by replacing the video board and tossing the old one. Of
course, if it's just a memory IC, perhaps that can be fixed later when there's
an odd hour to waste.
>
> > identical one, the fault in the serial port board can be fixed AFTER the
system
> > is running again. Otherwise, I have to fix the board first. If that's the
box
> > I use to order the parts needed to fix the serial board, I have a problem
that a
>
> It's interesting you mention the serial port -- yes those do fail quite
> often. But most of the time _on all the machines I have_ it's the RS232
> drivers/receivers that fail, not the UART or other logic.
>
True, but not if you don't fiddle with the cables. Moreover, even the few
minutes needed to desolder the transmitter, and that fails more frequently than
the receiver, for some odd reason, in my experience, you've still spent more
than the entire replacement card costs.
>
> Now, 95% (or so) of the machines I have -- minis, micros, etc -- use
> 1488s and 1489s for this. DEC, Philips, PCs, TRS-80s, all have them. The
> next most common chip is the MAX232. Then comes the oddball stuff.
>
several of my old S-100 boards use the 75154 and other somewhat odd parts. I
hand-wired a mezzanine card that plugs into the sockets occupied by two 8-pin
transmitter parts and one 75154 and replaces them with a 1488 and a 1489, just
because of that. Apparently there were supply problems or cost issues that
caused CCS to design with the TI parts.
>
> Now, I do enough designing/prototyping here that I keep 1488s, 1489s and
> MAX232s 'in stock'. It is actually easier for me to find a replacement
> chip than a complete serial board. It also makes a lot more sense to me
> to keep small parts that can be used to repair many different machines
> than complete boards that only fit one machine.
>
In recent years I've found it MUCH easier to find a replacement serial board for
a PC than a replacement 1488/89. The fact they're not so popular as they were
back when they weren't on the motherboard makes a difference. They cost
typically $1 for two at the local thrift stores.
>
> And it takes no time at all to find out which section of which chip is
> faulty. If you can't manage that, well....
>
> Now, what about the oddball stuff. Well, machines with odd RS232 buffers
> tend to be odd machines. And odd machines are not the easiest thing to
> find complete spare boards for. For example it's going to be a lot easier
> to get one of the serial buffer chips for my Apple Laserwriter than to
> find a complte LW2NT formatter board that happens to be configured
> correctly to work in my system. And in my experience it would take longer
> to configure one than it would to change the darn buffer chip.
>
> > board swap will fix and no other method will handle as quickly.
> >
> > Now, maybe swapping out the offending component won't fix some systems, but
I
> > don't have any of those.
>
> Odd, as I said, I don't have a machine where swapping parts _will_ fix it
> quickly and reliably....
>
I'm sure that with all your experience, the replacement of a faulty IC is
thoroughly executed and produces a reliable result. For me, though, since the
electricity to desolder and resolder a faulty component often costs more than a
replacement board, I prefer to swap the board. That doesn't mean I toss it
afterwards, since it can normally be fixed, and, eventually, there won't be
spares so readily available.
BTW, when I worked in aerospace, whole computer systems were considered
components in larger systems. I meant board-level components in my remark, not
an IC.
There was a time when I loved isolating and replacing faulty IC's. Sockets made
it easier, by far, and quick enough that it was worth doing. However, those
same sockets made the board more costly and less reliable. The sockets some
fellows liked best often allowed parts to fall out of them if the local fan was
running out a bit and caused vibration. I've seen plenty of them let go of an
IC as they were extracted from their backplane. I had a tough time convincing
some fellow micro enthusiasts that the common and readily avaiable TI
low-profile sockets really needed one to fasten down the IC's with a clip or
wire-tie if one wanted them to stay in place. Consequently, I developed a
liking for the later generation of gas-tight sockets that didn't let go so
easily, and, in fact, would take your fingernail off if you attempted to use it
to extract a part.
>
> -tony
>
>
Received on Wed Jun 13 2001 - 14:43:31 BST