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(Topic ID: 252890)

IC’s operating temperature

By oldschoolbob

1 year ago

Topic Stats

  • 44 posts
  • 9 Pinsiders participating
  • Latest reply 1 year ago by mbwalker
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    #6 1 year ago

    The hotter chips aren't AMI brand are they? I notice they run hotter.
    What voltage are you reading at the 5V rail on the MPU board?

    #8 1 year ago
    Quoted from oldschoolbob:

    TP5 reads 4.6 VDC

    TP5 is only 4.6 volts? Where are you losing the 0.7 volts from the power-supply to the board? What current reading are you getting on the 5V rail on your bench power-supply?

    #12 1 year ago
    Quoted from oldschoolbob:

    I hope I haven't lost you in my explanation.

    Yeah I remember most of it. But there was something about the current meter on the ground wire.

    Where do you measure the 0.7 voltage loss though?
    With a board powered on, measure the voltage across the 5V source on the power-supply banana connectors, then between the black banana connector and ground on the MPU board, then between the 5V banana connector to 5V rail on the MPU board.

    Quoted from oldschoolbob:

    Today I did some checking. I checked both the Stern board and the Bally. I got similar results.

    Back to the original question, how about the chip temperatures between the Bally and Stern boards on the bench? Similar or different.

    BTW, can I make a suggestion, every PC power-supply has the red wires as 5 volts and yellow wires as 12 volts. It's almost defacto. Feel like changing them?

    #14 1 year ago

    What about when the board is booted, what voltage do you measure across the power-supplies banana connectors (the connector outputs for your 5 volt supply)?

    #17 1 year ago
    Quoted from oldschoolbob:

    Strange thing when I measured U8 – left side measured 90 and right side measured 83.

    Might be stray heat coming from the 1 watt 82 ohm resistor near it.

    Are the warmer ROMs all ceramic packaging?

    #18 1 year ago
    Quoted from oldschoolbob:

    Wouldn't that be the same as measuring at the alligator clips?

    Ideally yes, but you're getting loss somewhere so we need to see if it's in the leads or the power-supply.

    Quoted from oldschoolbob:

    I can't measure at the banana connectors unless I pull them out.

    Just pull the banana connectors out 1/16" so you can get your multi-meter leads on the connectors to measure.

    #21 1 year ago
    Quoted from oldschoolbob:

    I'm guessing the Stern U2 is the only ceramic.

    Yep, the purple chips are ceramic: Your Stern U2 ROM and also that Bally U9 CPU. You might see some white Fujitsu EPROMs on these early boards that are ceramic too.
    Ceramic is a better thermal conductor than plastic so should be better at dispersing heat away from the internal silicon die but it can depend on the silicon technology/construction used.

    #24 1 year ago
    Quoted from oldschoolbob:

    Then I booted the board and checked TP5 = 4.71
    I pulled out the banana plug enough to get my probe on. 4.96 VDC.

    So you're losing voltage between the output connectors of the power-supply and the alligator clips on the end of the cable when loaded. Didn't you have some connection issues with those alligator jumper leads back when you were building your bench power-supply? You might want to check each end of those leads and make sure you have good solid connections to the alligator clips/male banana plugs.

    #26 1 year ago
    Quoted from barakandl:

    Maybe put a molex plug on it to plug into mpu j4

    Good idea, I've done this too.

    #37 1 year ago

    Post the schematic for the power supply again. Suspect it could be because of the current meter on ground.

    #42 1 year ago

    Well done, great to see you guys sorted it out!

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