(Topic ID: 300147)

PCB that needs a little repair, want to make sure I do this right

By jrebs

82 days ago

Topic Stats

  • 7 posts
  • 4 Pinsiders participating
  • Latest reply 82 days ago by jrebs
  • Topic is favorited by 2 Pinsiders


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    #1 82 days ago

    Hi folks, first post here of probably several. Loved pinball when I discovered it as a boy in the 80s but only just got my first machine, a 1989 Williams Police Force. There are a few issues I need to sort out with it, some more significant than others, but to start with I'm tackling this one which seems pretty straight-forward.

    This machine has had all the lights replaced with LEDs and some other updates. There is a lamp on the playfield under the "10K" middle ramp space that doesn't light. I did lots of tests and found that a known good bulb will not light there. Closer inspection showed what I *think* is a solder joint that came loose, probably while moving the machine across town to my place. I've included some photos. The area where the connection looks bad has some coloured smear around it, distinct from all the other joints. My guess is that this is flux (?) and an indication that this connection has been soldered by one of the previous owners, and that might be why it broke loose, as it was not as solid as the factory connections.

    My plan is to try to re-solder this connection, but what I'm unclear of is whether the circuit is exposed enough there that a new blob of solder would fix it. Looking at the area that has come off, it doesn't really seem like there's metal there. Is it possible that when the connection separated, it pulled some of the connective material off the PCB as well? Would it be a good idea/bad idea to sand or otherwise remove the discoloured stuff (flux?) from the area before I attempt to re-solder it?

    Sorry if this looks plain as day to seasoned pinheads. I've never tinkered with too much electrical stuff (I'm a software programmer by day) and want to use great care before doing anything potentially impacting to my first table (of hopefully more to come).


    PS: I declined the suggestion to link this post to the game in question because I think the particular game is not really relevant to the subject, but if the SOP on this forum is to link them even in a case like this, please let me know and I'll adjust that in future threads.

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    #2 82 days ago

    On my lunch break I took out a multimeter and did some tests to confirm if there's any connectivity there. As I suspected/feared, it doesn't seem like the solder joint has any copper trace to grab on to. I was only able to make connection when the tip of my multimeter probe was pointed directly to a very precise spot around where the green arrow is. The red arrow, no dice. I'm thinking I'll need to expose a bit more copper below the green arrow and then I guess trail a big blob of solder to it?

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    #3 82 days ago

    An easy way to test these light PCB's out of the game is a 9v battery and a couple of alligator clips.

    The sockets do go bad. They can lose tension on the bulb or break all together. Or the 2 arms don't quite make full contact with the PCB. You can try bending them downward slightly. Also you can and should refresh the connection point between the lamp socket and the PCB. Do you see those little dots/impressions in the crescent areas on board? Take your soldering pencil and reheat those areas. You can add a tiny bit of solder to the area, just make sure you keep things level and even. Those indentations can cause bad connections as well. The last point of failure is bad/cold solder joints on the connector itself. Reheat each pin with a little fresh solder to make sure those are good to go.

    As to your proposed fix, yes that would work but I would check everything else first.

    #4 82 days ago

    I would not go with a big blob of solder. If this was a repair I was making, I would expose the remaining trace on the PCB, clean off all that dried flux, and then use a short piece of thin-guage solid copper to make a "jumper" from the existing blob to the exposed trace. Delicate work but can be done.

    #5 82 days ago
    Quoted from John_C:

    I would not go with a big blob of solder. If this was a repair I was making, I would expose the remaining trace on the PCB, clean off all that dried flux, and then use a short piece of thin-guage solid copper to make a "jumper" from the existing blob to the exposed trace. Delicate work but can be done.

    I googled this and it looks like the ticket. I'm going out tonight anyway so I hope to find some copper foil tape to do this. Can you suggest the best way to remove dried flux? Would 99% isopropyl do it?

    Thanks also for your suggestions Xenon75 , I do see what you're referring to with the crescent shaped contacts for the lamp fixtures. I did test with a lamp fixture installed and they are making good contact on both sides and it appears confirmed that the identified missing connection point is the issue. I'll probably clean up those contacts at the same time as the required fix for future generations.

    #6 82 days ago

    If you have a 1N4004 (or 1N4007) diode lying around then:

    • Cut the old one off.
    • Remove the legs from the pads.
    • Remove all the solder from the pads.
    • Scrape or sand the solder mask to the twist lamp pad.
    • Install the diode and bend the excess lead over to the exposed trace to the twist lamp pad.
    • Solder the diode in place and the excess lead to the exposed trace.
    #7 82 days ago

    Then God said, "Let there be light"; and there was light.

    Thanks for the tips, pinheads.

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