Need desoldering advice

I was working on a lathe with a Fanuc 0-TC control today that could not download programs and I suspect the 751488 line driver. Disabling Xon/Xoff let us load a program. I ohmed the db25 connector to M5 on the memory board. The wires are good. One of those led things you plug in shows no activity on Tx coming out of control. Iow, it hears fine, but is mute.

I have a new memory board on the way but would love to replace the chip and have a spare for the other machine of this type. I remember seeing a tip that was the outline of a 14 pin dip years ago but I can't find it now.

What is the current best practice for desoldering 14 - 16 pin DIP packages? What is the lesser expensive options? ;)

Thanks,

Wes

download programs

program. I ohmed

hears fine, but

outline of a 14

Firts clip it loose and then suck / blow out the solder using a bulb type desolder device, lastly heat again and one by one pick out the remaining leads using a roachclip or fine tweezer.

Be really careful its actually pretty easy to mess up a multi layer board if you go into it halfhazardly heating / pulling on the old component IOW dont try and play dentist removing teeth here.

As was suggested cut the leads close to the IC. Now, provided you have enough clearance above the board, straighten the cut off pins vertically. Then using a fine point soldering iron solder an IC socket pin by pin to those on the board. This way there is less chance of damaging the board traces.

Chuck P.

download programs

program. I ohmed

hears fine, but

outline of a 14

For desoldering, the integrated solder sucker soldering iron that has the spring loaded plunger type vacuum pump will do the job. A real desoldering station is of course better. Solder wick is a last resort.

The all-at-once type tips aren't great since they leave the solder clogging the device holes in the PCB. Think of them more for salvaging useable parts, than for rework.

Be glad you aren't trying to rework a surface mount board, they can be a real pain in the posterior without special tools.

If you have never don't this before, here are a few tips.....

First off, its really easy to de-laminate the copper traces and pads from the fiberglass board, with to much heat!!! don't use that big old 100/300 watt soldering iron!! use a 15 watt cheapo from radio shack. Don't work on each pin in a row, alternate pins or give the board a little time to cool, between operations....Its not hard, just use common sense.

First before you even start, mark the board where the "U" shaped notch on the chip is. If you don't you might forget which way the chip goes on the board.

Next cut all the chip legs, as close to the chip as you can. The left over bits of the legs on the board will become handles when you take desolder them. I would suggest maybe getting one of these

desolder with. You can hook it up to a normal light dimmer and cut the wattage way back, because the one listed is 45 watts, a little to big for my tastes. What your trying to do here is remove the cut off legs and open up the through hole on the board with heat and suction. Once all the holes are open, you can install a chip socket, then its really easy to replace the chip the next time it cooks.... Just go slow and keep cool (pun intended!!!)

here is a great site, yes I know its about pinball machines, but it does have a great section on desoldering and soldering both...

also on the same page look at section 3.f how to use it:soldering a circuit board...

Hope that helps...

Bob in phx (who has burnt up his fair share of circuit boards, both with a soldering iron and electricity too!!!)

The advice to clip the pins is really the safest way to remove the chip. A Dremel cutoff wheel works pretty good as does a very fine pointed pair of cutters. There are desoldering tips made to heat all pins at once and there are also spring loaded clips to pop the chip off when the pins are free. There are also hot-air desoldering systems but all of these things work better with experience.

If possible, my advice would be to have someone experienced do this while you watch, if you want to be sure not to damage the board. It's not difficult but it is easy to make a mistake.

Don Young

Wes -

You got good info on the desoldering DIPS.

My concern is are you sure ?

Also - are all the gates being used ? - maybe not - might be able to cut and jumper - to the DIP and use a unused gate. Looks like a quad dual input Nand Gate.

Martin

Mart> I was working on a lathe with a Fanuc 0-TC control today that could not

download programs

program. I ohmed

hears fine, but

outline of a 14

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Very easy to do with vacuum equipped desoldering station. Maybe you can rent one for a day.

i

download programs

program. I ohmed

hears fine, but

outline of a 14

I'm not sure on if all gates being used. This being a Fanuc item, there is a perfectly good serial port next to the one that is broken but turning it on is an expensive option.

I'd like to put a scope on the input side of line driver before I pull the card to make sure I see data going in.

Wes

Iggy, Make your own desoldering station. A small vacuum pump (I used the guts of an old daisy seal a meal), the radio shack bulb desoldering iron, a chunk of rubber hose and a filter if you think you need it (I used a baby food jar with to brass pipes soldered in) Add a light dimmer and you have temp adjust too.... I built one and it worked great for years and years. I then was given a real pace handpiece and it works just as well as the modified radio shack one!!!!

I have a working one... Pace 2000

i

AND WAY TOO MUCH OF IT TOO

I

I would STRONGLY recommend against a socket - in general experience has shown that the sockets are less reliable than the chips - if you expect to be changing it a lot, a socket is good, otherwise, eschew it

** Posted from **

William, I would respectfully like to disagree. Machine pinned sockets are very reliable. I have never worked on the control boards for this machine, but I have had years of pinball machine repair and have never once had a machine pinned socket fail. Pinball machines live in a very hostile environment, with vibrations, liquids, smoke and all other sorts of mechanical and electrical stresses. The dual wiper sockets (scanbe brand) are indeed bad, but not the machined ones...just my opinion, no disrespect intended.

Wes,

Wow - a popular topic tonight. I suggest a couple of things that I didn't see mentioned:

1) BACKUP the machine if you don't have a very good parameter list. (Naturally, you'll have to do this by hand since the port is blown).Things that get changed on the factory list include RS-232 parameters and backlash values. Fanuc 0C's have a supercap on the memory board that should hold the parameters while the board is unplugged. Sometimes the board gets laid on metal and the supercap drains. 2) Also, find out what blew the port. Mostly, they get blown because of bad / broken ground wiring on the PC side. Also, if the PC is plugged into an area of the building different from the electrical system running the machine tool AND the grounding is poor, high voltages flow down the RS-232 wiring.

Warren Uptime Electronics, Inc.

How did you find that 751488 is is the serial chip, and where did you get a replacement chip? I know of a couple machines here with the

0-TC control, same issue, cannot send , but can receive with the serial port.

samurai.

hears fine, but

My first job out of tech school was repairing pinball machines for an amusement operator. I second the socket idea. Less of a chance for a newbie to fry the IC. I've installed plenty of them. I've never had a problem with socket failure.

Folks seem to like the solder suckers, but I like the chem-wick braid. It's easier to pack > William,

Use machined pin sockets and the reliability goes WAY up - and no chance of overheating the chip soldering it in.

** Posted from **