MPU BOARD REPAIR
There are many things that can wreck an otherwise decent Pinball PCB. When boards were in the hands of Dealer Techs there was only a slight chance they could muck up a customers' repair. If they did- that Mucked up board would be slid into a box under their bench and a new board would quietly appear from the parts room (charged against a traded in pin). This would eventually cease as the Tech got better. Move ahead 10 years and many games are now in private ownership. At first those owners went back to the Distributor for parts and help. When the Dealers gave up selling Pins (new or used) owners turned to the Net for help. Vendors popped up everywhere offering parts and advice. Some actually knew what they were talking about, a lot of them didn't and some still don't. Rather than build some type of test fixture and offer repairs they opted for the "Replace the board with this dandy new one OR put on one of my 'Repair Kits' ". They would never get involved with the customers' actual installation of any of these products, so if things went sour...they would simply imply that the Part/Kit was good, (the customer didn't know what they were doing).
After repairing Boards for 30 years I have picked up some established benchmarks for examining MPU's to determine if they can be repaired. Let's face it..ANY MPU (no matter how rough) can be brought back from the dead. But not in the time frame that a repair shop can afford to spend on one board. There are plenty of well meaning techs that find a great deal of satisfaction repairing those really bad MPU's that no one else will work on. In the final scenario most really bad boards will always have some lingering problems with flickering displays/ lamps and inconsistent game behavior. The tiniest speck of corrosion can short out any one Data line to another. That brings us to the most useful tool in the rebuilding process of any MPU/CPU.
Media used is fine Silicon.
It takes a little skill to manage one of these guns because staying a little too long in one spot can blow a hole thru the board. There is nothing better to solder on than copper left behind on a Bead Blasted PCB. Only a little sanding (after blasting) is needed to get the copper shining and solder ready. I'm not sure how many of these machines are in use by other techs but a board repair is only 1/2 finished without one!
Following shots show areas that were blasted then new parts replaced. The same process can be done with a 'repair kit' if the owner knew exactly which parts to use from the kit. Replacing all the kits contents doesn't make sense and will leave behind a mess of lead lumps on parts that were soldered onto corroded stumps (because solder wouldn't flow). I refuse to work on 'kit' boards because it's a double repair. First-remove all the "kit krap" before bead blasting ...then start the repair all over.
BEFORE BLASTING AFTER BLASTING
After bead blasting and sanding the area around this (Bally) U8 socket, the final cleaning will consist of sliding some solder wick across the pads to pull up any residual solder and then prep copper for soldering. Finally, inserting machined pin socket strips to accept a fresh CMOS 5101 Ram.
In addition to socket replacement there are several other parts that will need to be replaced in the affected area. After a complete cleaning/sanding the board testing begins. When the performance of the self test is satisfactory the final set of (new if needed) game roms (2 X 2732 U2 & U6) are plugged in and board is left to burn in for a few hours. Repeated on/off interrupts are done to see if Flicker/Flash routine is OK too. Finally, a battery backup consisting of a holder, 3 AA batteries, are installed. Score levels are set to check on the boards memory retention.
All this (and return postage) for $75.00 and in a less than 5 days turnaround.