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channelmaniac
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« on: September 15, 2008, 10:14:08 PM »

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.
« Last Edit: September 15, 2008, 10:20:16 PM by channelmaniac » Logged

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« Reply #1 on: September 15, 2008, 10:19:56 PM »

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.
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« Reply #2 on: September 15, 2008, 10:30:40 PM »

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.


* Patching traces.jpg (110.32 KB, 640x427 - viewed 919 times.)
« Last Edit: February 02, 2009, 10:52:22 PM by channelmaniac » Logged

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« Reply #3 on: December 02, 2008, 12:50:48 PM »

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 tip

For 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.
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« Reply #4 on: December 02, 2008, 01:01:53 PM »

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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channelmaniac
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« Reply #5 on: January 18, 2009, 11:58:13 PM »

Cleaning leaf switches

Arcade buttons are typically one of two types, snap switches or leaf switches. The leaf switches are old school and are preferred by many collectors, but what do you do when the switches don't make good contact?

The switches have metal arms and as long as they aren't cracked, they can be bent back into position. If this doesn't fix the switch the next step is to clean the contacts.

Cleaning the contacts requres a simple, but special tool called a burnishing tool. You can find this at your local NAPA Auto Parts store as it's used for cleaning and polishing points in a distributor on older cars, motorcycles, and other motorized vehicles. They are cheap and are THE PROPER TOOL for doing this.

NAPA calls it an "Ignition File". Item#: SER2153, Price: $2.99

Don't use sandpaper or a sharp kinfe to polish the contacts on the switch, you'll only end up with more problems and with those problems returning sooner. As a plus, this is the same tool needed to clean contacts on old electromechanical (EM) pinball games and slot machines. If you are a collector of old machines, you'll get a lot of use out of this simple tool.

Don't just replace the button with a snap switch type, restore the old game back to it's original shape by simply cleaning those leaf switches!
« Last Edit: February 02, 2009, 10:56:22 PM by channelmaniac » Logged

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« Reply #6 on: February 07, 2009, 11:48:16 PM »

Fixing burnt edge connections

Some arcade games have a BAD habit of burning the edge connectors. Some of the worst culprits are:

  • Pac Man / Ms. Pac Man
  • Pac Man Jr.
  • Pole Position I / II

But it's not too hard to repair the power traces on these boards with some simple copper trace tape. What makes it easier is that the traces are the same on the top and bottom of the board. This allows you to take the tape and run it from the top, across the edge, and to the bottom of the board.

What happens is that the contacts on the harness loosen over the years. The connectors also oxidize and start making bad connection with the board. As the resistance to the current goes up, so does the heat which burns up the connector. Now, on to the repair!

First, take a sharp hobby knife and score a cut across the damaged PC board trace then peel it off the board. Tin the remaining edges of the trace then remove the solder.

Clean the PC board with some acetone or alcohol and Q-Tips then lay down some new copper trace tape. Start by slightly overlapping (1/16 to 1/8") the remaining tinned trace. Fold it over the edge of the PC board and across the bottom of the edge connector the re remaining tinned trace. Smooth it into place with your fingernail.

Put some solder on the top of the trace tape then on the remaining old trace. Bridge the 2 together to finish it. Do the same to the other end of the trace tape.

When finished you'll have a good connection point that will take the current necessary to run the game.

WARNING: To keep this from happening yet again you MUST replace the card edge connector socket on the wiring harness in the cabinet.

Also, if the board is too damaged under the burnt trace you may need to use some extra materials such a fiberglass/epoxy combination to build up the board with sanding to finish.


* Edge Connector Top.jpg (54 KB, 640x258 - viewed 709 times.)

* Edge Connector Bottom.jpg (46.87 KB, 640x231 - viewed 682 times.)
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« Reply #7 on: September 02, 2009, 04:39:49 PM »

Repairing boards when components have been ripped off.

A customer had a board that was listed as "damaged in shipping" - a chip and a capacitor were "knocked off the board." The repair of this board was complicated in that many of the pads were ripped right off the board along with some traces under the chip.

How do you repair such a problem?



The answer: With patience, a mulitmeter, some tools, electrical tape, kynar wire wrap wire, and a bit of fingernail polish.

First thing to do: clean the board. Remove excess solder from the pads and clean up any flux or other compound from the board.

Next, use a multimeter on the continuity setting to pinout the traces. In other words, where did the pins connect to? This may require following traces on both sides of the board! Use a magnifying glass to check for pins that connect to each other under where the chip body would've been or where a pad for a pin would've been. Use an ultra fine tipped sharpie to mark each location on the board where you can solder a wire jumper to go back to a specific pin on the chip. Don't be afraid of using a sharpie! When the repair is done, flux cleaner will remove the marker too.

If you can't figure out how the chip is wired in, try looking up the datasheet for it on http://www.datasheetarchive.com to see if there are any sample diagrams in it. Or, get a more powerful magnifying glass or a jeweler's loupe to see evidence of where the traces went.

With the pins figured out it's time to mount the chip. Make sure the pins are clean of excess solder on the bottom side where they come in contact with the solder pad. Put a tiny dab of fingernail polish down under the middle of where the chip mounts. Set the chip down on it and align the pins on any pads remaining. Use your liquid rosin flux on the pins/pads that are there and solder the chip using as many pads as you can to hold it in place.

Now use the 30ga Kynar wire to connect remaining pins to where the signals go on the board. Strip the end of the wire and solder it to a pin on the chip. Lay the wire down on the board and use your fingers & fingernails to route the wires as needed. Don't worry if they stick up off the board! Cut it to fit, strip the other end carefully, tin it, and solder it into place.

Now if the other end of the solder connection is too small for you to solder to then try to solder to a plated thru hole. You'll need to gently scrape the coating off to get to bare copper. Tin the copper then solder the wire to the plated thru hole.

If you must solder to a surface mount chip pin then use liquid rosin flux to help keep the solder joints from bridging or going cold. Double check your work to make sure you didn't bridge the solder across multiple legs on the surface mount chip. If you did, use more liquid flux and a clean iron tip to draw away the excess solder. It works like magic. Cheesy

When the last wire is done, straighten up the wires and test. If all works well then clean the board with flux, tack the wires down in various places with electrical tape, and use dabs of fingernail polish to hold the wires and chip in place. When the polish is dry, remove the tape and touch up the polish as needed.

When done, you should end up with something that looks like this AND something that works!



Enjoy!
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« Reply #8 on: March 07, 2010, 11:19:37 AM »

Using ROMIDENT to troubleshoot a board

If a game won't boot enough to run built-in self tests, it can be difficult to troubleshoot. Additionally, if facing graphic corruption, keep in mind that most game boards do not have the ability to test graphic ROMs so how can you tell if a ROM is bad? The answer is easy: use ROMIDENT.

ROMIDENT Download
Newer database of ROMs
WinROMIDENT

Simply unzip ROMIDENT into a directory on the hard drive. C:\ROMIDENT works well for this, BUT before ROMIDENT can be used to ID a ROM image, the chip must be read and the file saved to the hard drive. AVOID putting ROMIDENT in a directory off the desktop as this will require a VERY long change directory command to get to it. For example: c:\documents and settings\username\desktop\romident

To use ROMIDENT, save the ROM image to the directory where it is located, open a DOS prompt, and type in: ROMIDENT xxxxxxx.xxx  (where xxxxxxx.xxx is the file name of the ROM you wish to check. The easiest way to do this is to save it on top of the unknown.bin file repeatedly to avoid cluttering up the directory with ROM images.

ROMIDENT will then display the file name, checksum, and the ROM name plus what game it is from. For example:

Code:
C:\DOCUME~1\Owner\Desktop\ROMIDENT>romident unknown.bin
ROMIDENT v2.1
Thierry Lescot, 1998/99.

DAT file revision 3727.
UNKNOWN.BIN  [c1e6ab10] = PACMAN.6E    from Pac Man (Midway)

C:\DOCUME~1\Owner\Desktop\ROMIDENT>

However, there are times when you get the following:

Code:
C:\DOCUME~1\Owner\Desktop\ROMIDENT>romident unknown.bin
ROMIDENT v2.1
Thierry Lescot, 1998/99.

DAT file revision 3727.
UNKNOWN.BIN  [d016686b] NOT FOUND!

Which means that ROMIDENT does not know what the ROM is from. Take the checksum d016686b and run it through the Google or Yahoo search engine. This particular checksum comes back to gg1-7b.2c in the Galaga ROM dumps for MAME.

If the ROM is unknown to ROMIDENT AND is unknown to Google or Yahoo then there are 2 possibilities.

1. The ROM is bad
2. The ROM is from a version of game unknown to the MAME team.

Check another ROM from the board. If it's known then you can assume the unknown one is bad and needs replacing. Use the MAME dumps to get the ROM image needed to replace the bad one.

Enjoy!
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« Reply #9 on: March 07, 2010, 11:33:24 AM »

Using MAME to troubleshoot:

If a board has graphic corruption it can be tough to troubleshoot if the ROMs are soldered in. The easy way around this is to use MAME for troubleshooting.

For example: A Top Hunter game cartridge was sent in for repair with a complaint of "color issues" which turned out to be a graphic corruption problem. Additionally, it was a bootleg. Bootleg carts are generally full of cold solder joints which means every ROM has to be resoldered. This usually fixes bootlegs, but not this time.

The board had jumpers on it and those were verified to be in the correct position by comparing them to a picture of a working cartridge board set. The board had no gouged traces which meant the board most likely had a bad ROM. To troubleshoot this meant desoldering all of the "ROMs" and testing them one by one which is time consuming. These ROMs were actually flash chips soldered to 42 pin DIP adapters and their big square pins meant changing out desoldering iron tips too.

To use MAME for troubleshooting requires:

  • The MAME software
  • A file containing the ROM code for the game
  • WinZIP or other way to read/write ZIP files

Take the file for the game and play it in MAME to make sure it's working correctly. Next open the ZIP file containing the ROM images and replace the suspect ROM images one by one with a zero byte file. The easiest way to do this is to right click on the Windows desktop and choose New > Text File and give it the file name for the ROM image. Once done, rename the original ROM image name to something else such as adding a ".old" to the end of it then put the 0 byte file into the ZIP archive. Run it in MAME and make note of the corrupt graphics.

If that wasn't the correct graphics corruption then replace the original file and move on to the next ROM image.

For this Top Hunter cartridge this meant doing these steps for the C1 through C8 ROM files. The C7 and C8 ROMs both gave graphic corruption that approximated what was being seen on the game. Desoldering C7 and reading it in the EPROM programmer resulted in a checksum that was incorrect. Replacing the chip with an EPROM with the correct ROM image code fixed the cartridge.
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