NLG Users Repair Logs and Other Ramblings. Request your very own topic. Just ask any site staff. > Channelmaniac's Arcadecomponents' Old School Repair Logs

Repair and Recovery Techniques

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channelmaniac:
Fixing custom ICs with fragile legs.

This is DIRECTLY related to working on Galaxian, Pac-Man, Ms. Pac-Man, Galaga, and other Midway/Namco games of the early 80s. These games used chips by TI and General Instruments that had thin metal legs with silver plating. These pins are prone to corroding and since they are thinner than typical chips the legs tend to either fall off because of that corrosion or simply snap off when pulling them from sockets.

These chips are the causes of strange probles on the games. Take the chips out of their sockets and CAREFULLY clean the corrosion off the pins. A dremel tool with a wire brush attachment works wonders on those legs IF you are careful with it. It doesn't take much to clean the legs up.

If a pin has broken off it will typically happen where the leg thins out to fit into the socket. Take a junk chip (bad EPROMs are a great source for this!) and cut the leg off close to the body of the chip. Solder that leg onto the broken leg on the custom chip to repair it.

channelmaniac:
Recovering data from broken EPROMs.

EPROMs with bent pens are problematic in that when you go to straighten them they have a great chance of snapping off at the body of the chip. The more important the EPROM the more likely it is to happen.

If this happens and you need the data on it then the Dremel tool is your new best friend. Small cutting heads (metal ones, not grinding ones) can be used on the black epoxy cased ICs if you have a steady enough hand. Slowly whittle at the chip body to expose the chip leg.

If it's an EPROM with a ceramic case then use a thin cutoff disk to chip away some of the white epoxy material to expose more of the chip leg.

Once the chip leg is exposed, put the chip into a wire wrap socket. Solder a bit of Kynar wire to the top of the socket's leg, right next to the body of the socket. Tin the exposed leg of the chip and solder the other end of the Kynar wire to it. Once you have a good solder connection to the bad chip leg put the chip/socket combo into the EPROM programmer and read it. Once you have the data off of it simply program a replacement chip and put it in the game.

channelmaniac:
Repairing broken data traces on circuit boards

If you haven't noticed, I'm partial to Kynar wire. What is this? It's 30 gauge wire wrap wire. It's used for prototyping with wire wrap sockets and tools. It also makes for great trace repairs! It's tiny, easy to manipulate, and easy to route around and under ICs, transistors, caps, and more.

However, it is NOT for power and ground traces.

Invest in a good jewelers' loupe with a glass element and a good ring light with magnifier built in. These will come in VERY handy when trying to examine a board for cut/gouged traces. Next you want a good DIGITAL multimeter with continuity tests that beep.

When patching a trace it's easiest to solder from a pin component to a pin component but this isn't always available. When it isn't, follow the trace to the nearest plated thru hole. Use a sharp Xacto type knife to CAREFULLY scrape the green coating from the trace. Next, lay down a nice coating of solder on the newly cleaned plate thru.

Once good patch points are located on both sides of the damaged area then solder in a piece of the Kynar wire to patch the trace. It's easiest to do if you tin both solder points on the board then tin the wire before attaching it all together.

If the solder connection is to a surface mount chip then there are a couple of decisions to be made. If it's a big pin, it's easy to solder right to it. If it's a thin one then tin the wire and prep the chip by putting a thin bead of liquid flux on the pin to be soldered. Don't be worried about slopping it on there. It's hard to put too much down.

Put the wire on the leg of the IC then touch a clean soldering iron to it. If you have a little solder on it that would be helpful. Too much will just end up bridging legs and making a mess that will have to be cleaned up before trying to patch it again.

Once the patch work is done it can be cleaned up with rosin flux remover. Loose wires can be bent around with needlenose pliers to route them around as needed. They can also be grabbed in the middle with a small pair of needlenose pliers then slowly twisted to create a Z shape in the wire to help take up some of the slack. Once the wires are situated then tack them in place with some (non metallic!) fingernail polish.

Here's a picture of a Neo Geo MV4 4 slot board I repaired. This is a common repair job - the NiCd battery leaks then eats traces. The fix is to jumper the bad traces.

channelmaniac:
Straightening pins on surface mount chips:

When dealing with SMT chips on game boards you'll invariably find some with bent legs that MAY need fixing. MAY simply means that if they are bent but not shorting out to their neighboring legs then don't mess with it! If they are shorting then you'll need a couple of simple tools:


* 2 x Small Jeweler's Screwdriver - flathead type
* Xacto or other type hobby knife with a sharp pointed tipFor chips with bigger flat pins (SOIC, QFP, etc...) use one jeweler's screwdriver to put pressure on the foot of the pin while you use the other to gently pry the leg back into place. Be very careful to watch where the pin connects to the body of the chip. If it looks like it is splitting the STOP.

For chips with the smaller flat pins (SOIC, QFP, TSOP, etc...) use one screwdriver to put pressure on the foot of the pin and use the sharp hobby knife to slide between the legs and straighten them. Do this from the bottom towards the top. Use a slight twisting motion to separate the legs and use the sharp part of the blade to get as close to where they are touching as you can before twisting. DO NOT just "slide" the knife up the legs as you can cut the leg in two, which would be even worse.

Now the reason for putting pressure on the foot of the pin is to keep it from lifting up the pad or separating from the solder joint. Both of those are bad. Separating the solder means you'll have to reflow the leg and lifting the pad means you have an even bigger repair in that you'll have to patch a trace to a teeny tiny pin. Urg. Not only that but if you don't put pressure on the foot of the pin then when it lifts you'll likely end up with a straight leg but with a turned foot which is very hard to straighten out!

PLCC type chips that have the legs curled under don't generally have too many problems with bent pins but if they do, they usually break loose from the solder connection. Use the tools to bend the pin back from the top down. You may have to slide the hobby knife under the pin to bend it up slightly to clear the solder joint on the pad then to bend it down slightly to make contact with the pad after it is straight. Resolder the connection. If the leg still isn't meeting the pad you'll need to use extra solder to make it connect.

Dont' forget that if you need to reflow or resolder the legs on a surface mount chip using a soldering iron, use liquid rosin flux to keep the pins from bridging. It also helps if you have a standard or conical chisel tip that is CLEAN and in good shape.

channelmaniac:
Repairing cracked or broken circuit boards

Occasionally you'll need to repair a cracked or broken board as a replacement may either be too expensive, too hard to get, or take too long to get. There are some techniques that work well in repairing cracked boards and doing it in such a way that they are physically strong again.

The items you use to repair the board will vary. If the board is one that will get hot under normal use, DO NOT use superglues! If you read the label you will find cyanoacrilate (spelling?) as an ingredient. You do NOT want to breathe fumes from that stuff when it burns. This includes neck boards on monitors.

Glues to use can run from two part epoxy to JB Weld to super glues. I prefer the superglue gel and liquid hardener combinations when doing normal board repairs.

If the board has heavy power and ground traces then carefully scrape the coating off of the trace. Use a sharp knife to cut back any lifted parts of the trace to have a good solid surface to use. Tin the trace then tin some large gauge wire. I'll use anywhere from 22 ga solid to 16 ga stranded wire depending on the size of the trace to repair. Once the wire is sufficiently coated with solder, align the board pieces, epoxy or glue them in place, then solder the wire on top of the trace to not only connect the trace but to also give physical structural support to the board. Repeat this for each of the larger traces.

If the board is broken in two, another technique is to drill holes through the trace and use a larger gauge solid wire to do a jumper across the top of the board as well. This will not only give structural support on the bottom of the board but also on the top.

Smaller traces can be jumpered with 30ga Kynar wire wrap wire. Try to avoid the area of the board that is damage when routing the Kynar wire. I repaired a Shinobi arcade game board that had 8 small traces damaged when a corner of the board was busted. I routed these straight across the board rather than the circuitous route around the board.

Pick up a bottle of cheap fingernail polish (NON metallic type!) at your local dollar store. It works great at covering the solder connections and for tacking down the Kynar wire to make for a more professional looking repair.

RJ

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