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Thread: LM3900 Tester

  1. #1
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    LM3900 Tester

    My component tester can test most Op Amps but the LM3900 is a Norton Op Amp which work differently to most OP Amps and it's unable to test them.
    I remove a lot of LM3900's from Space Invaders boards and I wanted a way to test them without having to put them in a Spacies PCB, fit a test ROM and go through the sound tests. If I do this repeatedly it can cause issues with the sockets.
    I had a look through a Linear IC databook and found a circuit that uses all four Op Amps on an LM3900.
    I've used a 28 pin ZIF socket that I had on hand and the output connects to an oscilloscope to check that it's putting out the correct waveform.



    I knocked a PCB up on Vero board.



    Here's the result with a good LM3900.



    I'm not sure if I got the component values right as the PDF scan isn't 100% clear but it seems to work well enough (though not the correct waveform) to check all four Op Amps on the chip are working.

    I may do another one using a Squarewave Generator and repeat the circuit 4 times which will allow testing the four individual outputs separately.



    Same as this guy has done...



    Edit: I looked up the same schematic from another source and which is clearer and I should have used a 100pF cap instead of 100uF. Will see if I can find one on a parts board and swap it out.
    Last edited by Kaizen; 26th May 2019 at 07:41 PM.
    Namco Starblade - Taito Cocktail 14" x 3, 20" x 2 - NZ SI PtII Upright - Chase HQ DX, Taito Top Speed - Taito Grand Champion - Taito Safari - LAI SI Head to Head Cocktail - SI Cocktail Clone x 2, Pong Clone x 3

  2. #2
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    I knocked up a new board using the square wave generator circuit (x4).



    This one worked perfectly first go.
    The first video is of a good chip with all outputs working, the second one has a faulty chip with no output on amps 3 & 4.



    Namco Starblade - Taito Cocktail 14" x 3, 20" x 2 - NZ SI PtII Upright - Chase HQ DX, Taito Top Speed - Taito Grand Champion - Taito Safari - LAI SI Head to Head Cocktail - SI Cocktail Clone x 2, Pong Clone x 3

  3. #3
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    I got to thinking that it would be better if it was able to be portable and not have to be connected to an oscilloscope so I slowed the output frequency down from 1kHz to just under 10Hz and connected some LEDs to indicate that the outputs are working.



    The changed values are in red in the schematic below.

    Last edited by Kaizen; 26th May 2019 at 07:35 PM.
    Namco Starblade - Taito Cocktail 14" x 3, 20" x 2 - NZ SI PtII Upright - Chase HQ DX, Taito Top Speed - Taito Grand Champion - Taito Safari - LAI SI Head to Head Cocktail - SI Cocktail Clone x 2, Pong Clone x 3

  4. #4
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    I cheated and pulled the trigger on a BK570 back when eBay was doing the 10% off, up to $200, coupons early this year. Saved $100 on it.

    It was still crazy expensive for a small hand-held tester at $900, but that's just 10 Galaga board repairs.

  5. #5
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    I really can't see why these Linear IC testers are twenty times the price of the digital testers.
    With the Space Invaders boards I always socket and replace the LM3900s as a matter of course due to the high failure rate.
    I can test them in circuit which takes a bit of time but since I plan to replace them anyway it's easier to just remove and replace them all with new ones.
    It's nice to be able to quickly test the ones I remove for when I run out of stock on hand and just need to get a board tested with a known good chip but I can't justify shelling out well over AU$1000 on a tester when it will get limited use.

    Making this tester was a good learning experience on how the LM3900 works as well, it's quite a versatile chip.
    Namco Starblade - Taito Cocktail 14" x 3, 20" x 2 - NZ SI PtII Upright - Chase HQ DX, Taito Top Speed - Taito Grand Champion - Taito Safari - LAI SI Head to Head Cocktail - SI Cocktail Clone x 2, Pong Clone x 3

  6. #6
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    I decided to give this an upgrade and designed a PCB for it that will fit in a hand held enclosure.









    https://www.jaycar.com.au/black-hand...osure/p/HB5610

    The minimum order is for 5 PCB's so I'll have a couple spare if any paid members or veterans wants a bare PCB, just pay for postage.
    Last edited by Kaizen; 1 Week Ago at 05:36 AM.
    Namco Starblade - Taito Cocktail 14" x 3, 20" x 2 - NZ SI PtII Upright - Chase HQ DX, Taito Top Speed - Taito Grand Champion - Taito Safari - LAI SI Head to Head Cocktail - SI Cocktail Clone x 2, Pong Clone x 3

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