(Topic ID: 134377)

Big Brains Needed...G System 1, 5V at 1/2 output.

By lpnsocal

4 years ago

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  • 9 posts
  • 3 Pinsiders participating
  • Latest reply 4 years ago by lpnsocal
  • Topic is favorited by 1 Pinsider


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    Gottlieb_Sys_1_Power_Supply_Schm_07292015_0001.pdf (PDF preview)

    #1 4 years ago

    Before I throw in the towel and buy an after market Sys 1 power supply board, I thought I'd throw this out to the Great Pinball Gurus!

    After I spent 6+/- hrs testing and replacing components I took my 2 boards w/ same problem to my board guy and we spent another 4 plus hrs duplicating some of my previous efforts, retesting and replacing more components. All to no avail, still 2.4v - 2.6v at the 5V pin(A2P2.) All input voltages(A2P1) are correct. Let's see if I can remember all replacements;

    7 pin Connector(A2P1), CR1 & 2, CR 3 & 4, Q1, IC1, CR5, CR101 & 201, Pot R4, CR21, R21,LIC1, additionally C1 w/ supplemental grounding line added.

    Additional info...., -12v good, 60v and 42v good on A2P3 , as expected 4v & 8v virtually nil.(can't remember exact)
    My board guy has a good board/working machine(Joker Poker). Oddly and likely meaningless, both bad boards are off Genie.

    Thoughts, suggestions, directions(even toward the fridge) are welcomed.

    #2 4 years ago

    Without looking at schematics or specifics to the game (sorry if this is quick an stupid) but, whenever I hear 1/2 voltage problems I think of bridge rectifiers and wrong AC/DC settings on the DMM for the test points.

    #3 4 years ago

    Thanks for the Reply, I'm fairly certain there's no bridge rectifier on the power board, and voltages to board measure out correctly. Somewhere in the convoluted mess of them tweaking the incoming 11.5 VAC it doesn't quite make the 5DVC outgoing to the MPU.

    See attached.Gottlieb Sys 1 Power Supply Schm 07292015_0001.pdf

    #4 4 years ago

    Re test CR1 and CR2 the 1n5401. They should be 3amp, 100v rectifier diodes. Look for cracked solder joint also. Those will be doing the same thing a bridge would have been doing and an open connection at one of them will cut your voltage in half.

    If not, the schematic show plenty of voltages along the way. They are not test points so you'd have to be careful. But you should be able to narrow it down. But you already replaced the usual culprits. The UA723 (IC1) and Q1 are the main ones.

    #5 4 years ago

    Make sure Q1 is connected. If you have an open circuit on one of the legs you get a 2.5v on the 5v rail (dont ask me how i know this *grumble*).

    It is really easy to bust the through hole as you have to pull that transistor off to even get at the solder side of the board.

    #6 4 years ago

    Our initial test on CR1 & 2 tested good, however because of the disassembly of the board and backing plate every time a component is replaced(because of Q1 mounted from behind plate and then soldered to board), we began to replace multiple components. Some I had replaced and/or were thought good or new, including CR1 & 2.

    I lik might be very tight working those tests on the front, but there's no getting to the back once assembled.

    Thx for the input!

    backing plate w Q1.JPG
    Sys 1 power board on plate.JPG

    #7 4 years ago

    @ barakandl

    Make sure Q1 is connected. If you have an open circuit on one of the legs you get a 2.5v on the 5v rail (dont ask me how i know this *grumble*).
    It is really easy to bust the through hole as you have to pull that transistor off to even get at the solder side of the board.

    Forgive my less than perfect reply technique, but this is fairly new to me.
    The Q1 was actually replaced(in our process) a couple of times, the insulator is good(even for thru holes) mica and heat sink goop good. Are you maybe speaking of the thru holes on board that have the metal circles that the solder joins the board to pins?

    #8 4 years ago

    Use the schematic linked above and a DMM on continuity mode. Make sure the transistor is connected to the next components. You are relying on a solder joint to melt all the way through the board and connected on the other side. Repeatedly removing the can transistor damages the through holes and you end up with an open circuit.

    #9 4 years ago

    Thanks, I will share that info with my board guy/friend in possession of both boards. Did I mention, both boards have same issue, he's never seen this.

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