Re: RE: Pac repair

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I too have settled on the silver Soldapulit as my desoldering tool of
choice. This one is anti-static as well as a good sucker! I find that I can
be heating one leg, while pumping up the Solda with the other, then by the
time the solder is molten I can place the Solda in place (about 1/8 inch to
the side on the board and canted away from the solder point) then suck, now
move the tip to the next junction and at the same time pump up the Solda.
Hold up to a light to make sure all the solder is removed at the end.

You can get a nice rhythm going.

You must be careful NOT to let the Solda strike the tip of the soldering
iron, as this will damage the PCB trace. The tool bounces when activated
and you must make sure this bounce doesn't let the tool's tip strike the
hot trace or soldering tip touch point.

After the solder is sucked, I then use a thin screwdriver blade to push the
joint of the pointy end of the leg and feedthrough hole to the opposite
side of the feedthrough hole on the bottom of the board, and then press the
leg into the chip from the top side of the board at the junction of the leg
and the top of the feedthrough hole. This will normally release the IC and
I can then pull it out with my fingers (NEVER force out with a
screwdriver!!!). If the IC is still stuck use a pair of expanding jaw
pliers and grab the ends of the IC, and gently rotate it a smidgen back and
forth to find the stuck leg. Note this rotation is parallel to the face of
the PCB NOT up/down from the board!

I find I can pull a 40 pin IC in about one minute or so from start to finish.

John :-#)#

At 02:01 AM 12/14/00, Ranger Mike wrote:
>Well...
> A note on desoldering. For years I have used the little solder pump
>in conjunction with my soldering iron with much success. I tried out thew
>big blue soldaput pump here at work the other day, and it does a much
>cleaner job. I also, recently picked up one of the radio shack red bulb
>desoldering irons. I have found that the little pump works well for me, but
>is more cumbersome to use. If the chip in question is not bad, it is clean
>enought to stuff back in the socket. The RS red thingy, is way easier to
>use, but it does not have enough suction to clean the chip up well. The big
>blue, seems to me to be the best of three, while more cumbersome, cleans up
>the chip the best for re-use, should my trouble shooting technique fail me
>and I pull a good chip. I would really like to get a profesional desoldering
>system, but I'm to cheap :-)
>
>That's all for now
>
>Mike
>
>
>
>
> > -----Original Message-----
> > From: mike_ranger@dofasco.ca [SMTP:mike_ranger@dofasco.ca]
> > Sent: Monday, December 11, 2000 9:47 AM
> > To: rasterlist@synthcom.com; TechToolsList@flippers.com
> > Cc: Paul.Tonizzo@sybase.com
> > Subject: Pac repair using a chip comparitor
> >
> > Hi all
> > I was working in the shop last night on a pac that has been giving
> > me fits. I tried the "staring at it for hours" approach first, but that
> > did
> > nothing to fix it :-0
> >
> > Weird symptoms. With a standard set up, I was getting a screen full
> > of slashes and zeros, flipping every now and again. I replaced the vram
> > with one of Clay's most excellent products, and the board now went through
> > self test over and over. up to, but not including the cross hatch. Self
> > test showed nothing. Removing the two middle roms changed nothing as
> > well.
> > (that was a clue). I tried a special daughter card I have that runs MS
> > pac
> > with no roms on row 6. booted to currupt screen images, so I felt there
> > was
> > a problem in adressing the roms, or ram.
> >
> > Last night, on a whim, I decided to try out my new HP 10592 logic
> > comparitor. I set it up to check 8k becuase I noticed the IRQ was not
> > firing. The comparitor said it was fine. Since it was my first crack at
> > using the tool, I was not convinced. Going back to the adressing issue, I
> > decided to check the ROM selct lines, by 7N chip, 74ls42. The comparitor
> > showed 3 bad outputs on this. Swapped it and the board came to life.
> > Even
> > works with the original vram, so the bad chip could have been messing with
> > the RD signal. No sound yet, but I'll get that working :-)
> >
> > On the Logic comparitor. The HP is a nice little unit, but you must
> > get one with the zif card. This was an add on produced in later runs. It
> > allows you to configure your chip with dip switches, where the original
> > unit
> > shipped with cards you had to phsically alter to match the chip
> > characteristics.
> >
> > Others in the comunity feel he BUGTRAP device is a better
> > comparitor, but I have no experience with it, so if you are looking for
> > one,
> > you should investigate those as well.
> >
> > The logic comparitor will be pretty much useless on any tri-stated
> > device. It will not make a newbie a guru, and like any test equipment,
> > you
> > have to understand the it's limitations to use it effectively.
> >
> > Too bad I go sniped on that fluke model 90 z-80 thingy last friday
> > :-( Gusee I'm going to have to save up for one of them nifty 9010A's
> >
> > Mike
> >
> > To UNSUBSCRIBE from techtoolslist, send a message with "UNSUBSCRIBE" in
> > the
> > message body to: techtoolslist-request@flippers.com. Please direct other
> > questions, comments, or problems to jrr@flippers.com.
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Received on Wed Dec 13 10:22:17 2000