Gorf RAM board repair

[Scottacus]

I have a bad RAM board that I wanted to repair but I didn't know how many chips were bad on the board so I found a RAM diagnostic program written by Mark Spaeth http://www.ionpool.net/arcade/tech/ and had it programmed onto a 2532 ROM by Steph at hobbyroms.  The chip goes into the X1 slot and doesn't require a pattern board so you can use it as a part of your troubleshooting if you don't know which board is bad in your rack.



I knew that the board had bad RAM because whenever that board was in the rack, blue lines were drawn across the screen when it was in slot 6 and yellow when it was in slot 5.  Here is the board in slot 5 with the program running on the ROM board.



When I pressed the fire button I got:



So at least U13 was bad.  This program can only tell the first bad chip and you don't know if there are any others following it.

A year ago I bought a Aoyue 474 A++ desoldering station because it is a pain to try to desolder ICs.  This station works great for jobs like this so if you are looking for a desoldering station, this one works great and is relatively inexpensive.  I didn't know how many RAM chips were going to be bad so I pulled good RAM from another board and put them on this board.  Having a good desoldering station made this a quick job.



Here is the RAM board with U13 out. 



I replaced U13, put the RAM board into slot 6 and got...



So unsoldered U14, replaced it and got...



We are getting closer!  U15 was replaced and...



Life is good!  I replaced the diagnostic ROM with the game ROM and ran a test game.  Everything worked great, in fact I got one of my highest scores since 1982.



In his read me file included with the diagnostic program Mark asked for donations if you liked the program so I sent him a little donation for his work!   

[jennifer]

    I find it curious they blew right down the line like that, What do you suppose caused that? overvoltage?....Good job on this fix.

[Scottacus]

Jennifer thanks for your interest, I really don't know what caused them to go bad.  It is curious that they are all in a row so your guess is probably right on.  I am glad that the carnage ended at U15 and didn't continue down the line!  Now I need to pick up some RAM to replace the ones I pulled in the repair.

[lacanian]

Thanks for the post. Did you just replace the faulty RAM chips? What's the level of difficulty in finding the RAM chips that much your PCB? What's the common cause of the failure?
Thanks

[Scottacus]

The RAM for this board are easily found, I ordered mine from twisty wrist at around $2.65 a piece. 

These RAM are not socketed and I don't know what the industry standard is but if you are dealing with 18 pin soldered chips, you probably will want a desoldering station if you are doing any volume of chips.  The desoldering station keeps the heat that the chip and board is exposed to at a minimum.  Also these old solder joints typically have some oxidization on them so that reduces the efficiency of heat transfer from the iron to the solder.  To make matters worse, if you look at your board you might find that the solder has gone all the way through the board to the component side.  This is hard to suck out with a conventional piston or bulb solder sucker.  If that solder is not removed and you try to force the chip out, it can pull up traces on that side of the board that will require repairs...

These may all be things that you already know about but in case you don't I just want to let you know what the potential problems are.  If you have a RAM board from one of these Midway card racks (Gorf, Space Zap, Wizard of Wor, Robby Roto and Seawolf II), I might be able to help you out with diagnostics and repairs.  PM me if you are interested.

[SavannahLion]

Um.... if the chip is bad why worry about heat?

It's also not uncommon to clip the legs and pull 'em individually

[Scottacus]

You are right, I was thinking more about the good chips that I was pulling from the working board. 

If you cut the pins you can work on them individually which is nice and you can always add a heat sink (alligator clip) to help protect components.  Waiting between pins can also help the chip cool down but patience is a virtue seldom found in men 

[SavannahLion]

That's true....

Go find a junk board and practice soldering on the SMD components tough. You'll get better at soldering/desoldering the THC stuff, guaranteed.

Oh.. pick up one of those lit magnifying lamps as well. I think mine is something like 3x and I picked it up and Frys. Then go get some defogger stuff.

[Scottacus]

The new RAM showed up today from Twisted Quarter.  I soldered them into the open spaces left from the chips that were used to fix the bad board and now all four boards work!