INTRODUCTION TO 6 CD'S
This Troubleshooting Pinball CD is aimed at two segments of the Pinball hobby. The Collectors that gather all the pinball tech info they can find and the Game Owner repair group that will use the CD’s as a learning tool. The in depth repairs are for the Game Owner repair group. They are written in plain language with minimal ‘tech talk’. After more than 15 years of doing board repairs I have assembled many notes culled from those repairs and will try to explain the procedures I used to find the problems and then fix them. All of the repairs shown here were accomplished using a $10.00 VOM and a $15.00 Logic Probe. Some repairs were originally done using a (shop) Oscilloscope but I recently purchased an inexpensive ($150.00) hand held Belgium made Oscilloscope for this series of CD’s. For the more serious troubleshooting I recommend purchasing all three. Shown below are the three instruments recommended.
Using an oscilloscope may be difficult for some. There are many settings, and each one could produce a different signal image. To minimize this problem, I used the auto setting on my Velleman Scope for each of the readings shown on the CD’s. This will allow someone else (using the Auto setting on the same instrument) to achieve the same visual reading. VOM readings can vary a little from meter to meter with out indicating any real problem. The Logic Probe is used to indicate the presence of a signal that is high, low or pulsing. One or all of these instruments can shorten the troubleshooting procedure considerably.
The VOM and the Logic Probe are the minimal instruments needed. The oscilloscope will be needed to read some of the blanking signals on Williams’s levels six and seven CPUs along with some driver board signals. A Scope is also needed for voice and sound samplings on a Bally Squawk and Talk. Sometimes a scope is used for Clock signals on an MPU. The logic probe will be the most commonly used testing tool for the board repairs shown on these CD’s. Another item needed for repairs will be a solder station. I have been using this unit (from Jameco 1-800-831-4242) for many years and found it to be very reliable and is priced around $90.00.
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Jameco Part# 236110CJ
Also needed for board repairs are desoldering tools. These 2 inexpensive choices are better suited to the 25 year old PCB’s being worked on than any hot air or other type of ($300.00+) desoldering system.
The boards being worked on were manufactured during the “cost effective” circa 1978. They are typical one and two layer PCB’s with the ‘hole thru’ mounting system. Boards that are 25 years old are hard enough to work on even if they are clean but…..add in the newest hot item-“acid damage repair kits” or an old favorite residual acid damage left under the parts from a recent “cleaning”… or… evidence of repairs from instructions downloaded (pages 1 thru 30) from the web. With all these ‘marvelous mods’ to deal with, this type of desoldering equipment is best suited for the job. With Bally boards it has to be noted that a ‘additional cost saving step’ in the manufacturing of their 1978 PCB’s will prevent using even the mild vacuum produced by the pump shown here.
It can be better explained with this small diagram ] [ which represents a cross section of a PCB’s pad and hole. It is called ‘plate through design’ and refers to a pad on top and another on the bottom of the board with a metal tube (plated through) connecting both pads. Plate thru process requires drilling an oversized hole that allows for the precise metal plating thru the hole, from pad to pad, ending up with a hole sized for the wire lead to pass thru for soldering. Bally decided to skip this extra step and just leave the etched pad glued to both sides of the PCB with no ‘plate thru design’.
Any 80’s repair shop working on one of these “cost effective” PCB found that each pad and trace had to be desoldered with extreme care to prevent pads from lifting off the surface when heat was applied. Advance 20 years…. add in acid damage and dozens of previous repairs and it makes the simplest act of changing a socket a nightmare job. If you went near these ‘floating’ pads with a hot air or power pump desoldering tools the pads would disappear. For this reason I use the desoldering braid wherever I can. Using braid meant that the surface had to be as clean as possible, free from dirt and surface corrosion. Solder won’t move if there is any surface crap left on the board. That goes for soldering or desoldering.
For me cleaning the surface involved using a bead blaster with an extremely fine silicon bead. Even with a bead blaster it takes a lot of skill to clean a board without destroying it in the process. Regardless how carefully the blasting is done there is some copper plating loss in the process. The copper lost from bead blasting was already laced with acid holes or eaten down to less that half its original thickness.
After the bead blasting and all the leads are removed, the solder is removed from the pad holes using the braid. For the holes that won’t give up the solder (from either side of the board), I use a small piece of stainless wire (solder won’t stick to it), set it on top of the solder filled hole, heat the wire up and push the solder thru. The resulting lump of solder can be wiped off with some braid. After all holes have been cleaned, use some braid to clean up the pad surfaces. Finally (when you’re ready to solder), clean the surface with some very fine sandpaper or emery paper. Start Soldering immediately after shining up the copper so that oxidation (tarnish) can’t screw up the surface. If the copper gets dull before you get around to soldering on it, clean the surface again. IT HAS TO BE PRISTENE before the solder will flow over/around/under all the metal parts. This cleaning can be accomplished without a bead blaster (if this were done by hand by the game owner) but the time difference rules out of this kind of work being done for profit. Anyone can repair any board if the clock doesn’t matter.
A repair shop shouldn’t charge more for repairs than the board is actually worth even though some do. That is why 50% of the boards that showed up here for repairs were sent back because owner had put down an “acid damage repair kit” on top of a polluted surface and this would require cleaning up that repair before I could do mine. Problem with that scenario (besides double the time spent on repairs) is the undeniable fact that Bally boards are a ‘ONE SHOT’ repair. First one to work on any board sets the bar for any future repairs. For the most part, repairs done over the years by Distributor level repair techs were clean and neat. After the games ended up in the private sector the ‘shotgun’ repairs began to show up. That meant someone had replaced all parts starting in one corner and ending in another.
Then the boards began to have a ‘special’ look as “repair kits” began to show up. If there were 15 parts in the kit bag the customer didn’t have a clue which (if any) were needed so……….put them all in and TURN IT ON!!! The neatest repairs were the ones that indicated the owner couldn’t get the old parts up out of the muck (solder wouldn’t flow) so they clipped the old part off leaving a little piece of the wire lead stuck off of the board and piggy backed the new part on top. Or…..going to RS and buying a WIRE WRAP socket to so that it could be soldered to the corroded stumps left behind, ending up with a “socket on stilts”.
I got a reputation for being ‘fussy’ about my repair requirements until those very same guys opened up there own ‘repair shops’ and got some of those beauties in to fix. I don’t hear much carping from them anymore. Eventually (after 15 years) I just stopped repairing boards and concentrated on manufacturing replacement boards and now writing repair articles. These CD’s will be a text and photo combination with some hands on troubleshooting and repairs added in, explaining as I go. The format will be PDF allowing anyone to obtain an Adobe reader (5.0 and later) from WWW.Adobe.com.
As the repairs shown on these CD’s progress it will be obvious that clean strong soldering is job #1. Plenty of practice is needed until the results are similar to this:
Results like this can be attributed to both a major cleaning effort prior to soldering along with use of a 1/64” tip and water soluble solder. There are no shortcuts to good finished work but if you have the right tools and plenty of practice it can be learned. The first time you lay down that perfect solder joint you will know you’re getting there. When the one next to it won’t flow- you’ll know the cleaning wasn’t complete.