(Topic ID: 300414)

Bench Testing Williams System 3-7 MPU/Driver - 5V Issue

By Knxwledge

12 days ago


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  • Latest reply 11 days ago by Knxwledge
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    #1 12 days ago

    I wasn't sure where exactly to put this thread, as I'm not sure if I have a board issue or an issue with my power setup. I am attempting to bench test Williams System 3-7 MPU/Driver boards. I plan on making something more permanent in the future but for now I made a few wires with spade connectors on one end, and alligator clips on the other. I made 3 for 12v, 5v and ground, and hooked them into my arcade JAMMA test setup which is using a Suzo-Happ Power Pro
    image_2021-09-15_004237.png

    Power supply is good, and when I measure the power at the alligator clips I'm getting the proper 12v and 5v, but when I hook them up to the board, the 5v supply drops to ~3.6v. The 12v remains at 12v when hooked onto the board. I tried hooking them up at IJ2 and TP 9/TP 10. I'm trying to figure out if this is because the power supply is ill-equipped for the job, or it's something wrong with the board. I tried it on another MPU I have (that's very corroded, I didn't expect it to boot), and the 5v supply dropped to ~4.1v. This makes me think the power setup I'm using is insufficient.

    Any help appreciated, I plan on making a more permanent pinball-specific test rig in the future but just wanted to try it out with what I already had. Would like to figure out exactly why what I'm doing isn't working. Do I just need to crank up the 5v adjust? I'm worried that's gonna raise the 12v too high

    #2 12 days ago

    Dont crank it up. The 5V should be able to handle 15A load, and the CPU/driver combo needs about one amp. Check your connections. Measuring the current at 5V line would help - if it is normal then your power supply is faulty. Does any chip get hot on the boards?

    #3 12 days ago
    Quoted from Tuukka:

    Measuring the current at 5V line would help - if it is normal then your power supply is faulty.

    On my JAMMA setup I have a JAMMA passthrough connector which displays the voltage at the edge connector (along with giving me a compact way to test inputs), and it measures 5v. The JAMMA side works fine (I unhooked the 5v from the power supply even though there was no arcade board hooked up in the meantime though). I'm 99% sure it's not my power supply.

    Quoted from Tuukka:

    Does any chip get hot on the boards?

    I was feeling the socketed RAM/EPROMs/CPUs and didn't feel anything getting hot, but I can check the other chips when I'm back out there. I don't know that this board works, I got it in a bulk lot of stuff and was told that it's very likely working, but I'm not 100% sure. The previous owner soldered the bottom-entry male pins directly to the driver board so they're inseparable without desoldering. I plan on fixing it in the future and doing it right. In an attempt to isolate the issue I did grab another MPU I have which isn't connected to a driver board and it also had voltage drop on the 5v

    #4 12 days ago

    The power supply should not significantly drop its 5V output if current is less than 15A. And if the board draws that much, something should get VERY hot.

    #5 12 days ago

    I had a horrible time bench testing Williams and Gottlieb boards with alligator clips. My 5v was always below 4. I crimped up a molex connector and it solved my problem.

    #6 12 days ago
    Quoted from Cheddar:

    I had a horrible time bench testing Williams and Gottlieb boards with alligator clips. My 5v was always below 4. I crimped up a molex connector and it solved my problem.

    I will try this, thanks!

    #7 12 days ago
    Quoted from Cheddar:

    I had a horrible time bench testing Williams and Gottlieb boards with alligator clips. My 5v was always below 4. I crimped up a molex connector and it solved my problem.

    This solved my 5v problem, Im getting proper 5v and about 13.5 for the 12v (which should be fine since its unregulated).

    Board is still hanging at 2 leds lit. I noticed that PROM 1,2 and 3 are getting warm pretty quickly. The boards still have a lot of original Scanbe sockets and the AMI branded 6802s which from what I gathered are big no-nos and need to be changed ASAP

    #8 11 days ago
    Quoted from Knxwledge:

    This solved my 5v problem, Im getting proper 5v and about 13.5 for the 12v (which should be fine since its unregulated).
    Board is still hanging at 2 leds lit. I noticed that PROM 1,2 and 3 are getting warm pretty quickly. The boards still have a lot of original Scanbe sockets and the AMI branded 6802s which from what I gathered are big no-nos and need to be changed ASAP

    Great news. The pincoder roms helped me quite a bit with non booting boards

    #9 11 days ago
    Quoted from Cheddar:

    Great news. The pincoder roms helped me quite a bit with non booting boards

    I saw that. Do I need displays in order to utilize it or does it use the Leds on the board?

    #10 11 days ago
    Quoted from Knxwledge:

    I saw that. Do I need displays in order to utilize it or does it use the Leds on the board?

    Different tests do different outputs. I uploaded some videos he has listed on his site. One shows how to use a logic probe to verify the output on a board without leds

    #11 11 days ago
    Quoted from Cheddar:

    Different tests do different outputs. I uploaded some videos he has listed on his site. One shows how to use a logic probe to verify the output on a board without leds

    One last noob question, for the MPU to boot, does it need a driver board attached?

    #12 11 days ago
    Quoted from Knxwledge:

    One last noob question, for the MPU to boot, does it need a driver board attached?

    Some of the basic tests (leds, blanking) can work without. I'd try a 01A Leds without and with. If it fails with then there could be a short on the driver board pulling the 5V low

    #13 11 days ago

    yes the driver board needs to be attached to the MPU for it to boot

    #14 11 days ago
    Quoted from Rikoshay:

    yes the driver board needs to be attached to the MPU for it to boot

    Quoted from Cheddar:

    Some of the basic tests (leds, blanking) can work without. I'd try a 01A Leds without and with. If it fails with then there could be a short on the driver board pulling the 5V low

    Thanks guys

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