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Thread: neo geo cd black screen

  1. #1
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    jetblue's Avatar
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    neo geo cd black screen

    hi,got a neo cd toploader that needed service last month. thought it was a simple laser issue as it would not boot games. discovered it would not show main menu but game did spin. Av was completely dead,blackscreen,blank,wouldn't display or audio. using my own neo cd i swapped parts and found the av/power board is where the culprit was. the laser and motherboard were fine.
    did a cap change but it had no effect. checked all the caps with a cap meter and they were fine. With the help of thesteve,member here and on pcfx,we looked more closely at the cxa chip which provides av,i thought it was bad and was gonna do a transplant from my own neo cd to see if it works. he said to take volt readings and compare with my working one first. sure enough there was a discrepancy. L4 was a resistor that had 5.0v on both ends on a working unit,i got 5v on one end and 0 on the other in the faulty unit. thesteve said L4 is a choke or inductor and to bridge it. after bridging with a piece of wire the unit came back to life. here's a pic circled in red that needed bridging:



    other side:



    that's it,if you have black screen or no display look for other L series of chokes or inductors or whatever they are called and check them if any have died. do that first and don't bridge like crazy.
    hope this helps revive any dead neocd's and many thanks to thesteve who stopped me from doing a chip change


    heres my half assed volt readings of a working neo and the faulty one if anyone needs it,too hard to explain so il just leave it:

    meter set to 200 v
    power light to the left

    working unit

    power area

    r12 0 both
    r13 09.3 up 09.3 down
    r14 0 right 07.8 left
    r15 08.5 up 0 down
    r16 05.0 both
    r17 09.3 both
    r18 04.2 up 0 down
    r19 0 both
    r20 0 both
    r23 00.7 up 03.6 down
    r51 09.2 up 09.2 down
    r53 0 both
    r54 07.8 right 09.3 left
    r57 05.0 up 03.6 down
    r58 08.5 up 09.2 down

    c21 09.2 right 0 left
    c22 0 up 05.0 down
    c23 0 up 09.2 down
    c24 05.0 right 0 left
    c25 0 right 09.2 left
    c26 0 both

    q1 09.3 right 08.5 middle 09.3 left
    q2 05.0 right 04.2 middle 05.0 left
    q5 0 right 09.3 middle 0 left
    q6 0 right 09.3 middle 0 left
    q7 03.5 right 04.2 middle 04.4 left
    q8 07.7 right 08.5 middle 08.5 left

    d1 09.5 up 09.3 down
    d2 05.3 up 05.0 down
    d3 0 up 09.2 down
    d4 05.0 right 09.1 left
    d5 09.3 right 09.0 left
    d6 0 up 05.5 down
    d8 00.6 right 0 left



    av area

    r4 01.9 up 01.9 down
    r5 01.9 up 01.9 down
    r6 01.9/02.0 both
    r7 01.4 right 01.4 left
    r8 02.1 right 02.1 left
    r9 01.6 up 01.6 down
    r22 00.2 up 00.2 down
    r25 00.2 up 0 down
    r26 00.2 up 00.7 down
    r27 00.2 up 0 down
    r28 00.2 up 00.7 down
    r29 00.2 up 0 down
    r30 00.2 up 00.7 down
    r31 04.6 right 04.6 left
    r32 0 right 01.9/02.0 left
    r33 0 right 01.9 left
    r52 0 up 00.2 down
    r55 05.0 right 05.0 left

    ac8 + 01.6 - 01.4
    ac10 + 01.9 -01.9
    ac11 + 01.9 - 01.9
    ac12 + 01.9/02.0 - 01.9
    ac13 + 01.4 - 00.8
    ac19 + 05.0 - 0
    ac20 + 04.9 - 0
    ac21 + 05.0 - 0

    L4 05.0 right 05.0 left
    L5 05.0 right 04.9 left

    c5 02.1 up 00.2 down
    c6 02.1 up 00.2 down
    c7 02.1 up 00.2 down
    c12 0 up 00.2 down
    c14 0 right 05.0 left
    c15 04.9 right 0 left
    c16 0 up 05.0 down
    c17 04.6 right 0 left
    c18 01.9/02.0 up 0 down
    c19 02.5 right 0 left
    c20 01.7 up 0 down


    cxa

    1 0
    2 02.1
    3 02.1
    4 02.1
    5 0
    6 0
    7 05.0
    8 03.6
    9 02.5
    10 04.6
    11 0
    12 04.9
    13 01.9/02.0
    14 03.9
    15 02.1
    16 01.6
    17 01.7
    18 01.9
    19 05.0
    20 01.4
    21 01.9/02.0
    22 01.9
    23 01.9
    24 0



    flipped over now power light is to the right

    audio area


    r59 05.0 both ends

    ac2 + 07.5 - 0
    ac23 + 5.0 - 0

    c2 02.5 up 0 down
    c9 02.5 up 0 down
    c10 0 up 02.5 down
    c11 0 up 02.5 down
    c13 05.0 up 0 down

    d7 07.5 right 0 left



    opamp1

    1 02.4
    2 02.4
    3 02.4
    4 07.5
    5 02.5
    6 02.5
    7 02.5
    8 02.5
    9 02.5
    10 02.5
    11 0
    12 02.5
    13 02.5
    14 02.5

    Ic1

    1 04.9
    2 0
    3 04.9
    4 00.2
    5 01.3
    6 04.8
    7 00.7
    8 00.7
    9 04.9
    10 02.3
    11 02.4
    12 02.4
    13 02.4
    14 02.4
    15 02.4
    16 02.4



    L20 08.2 both

    r1 01.7 right 0 left
    r2 0 right 0 left
    r21 03.7 both
    r24 0 both
    r37 02.5 left 03.8 right
    r38 03.8 both
    r42 03.8 both
    r44 03.8 right 08.2 left
    r48 03.8 right 0 left
    r47 03.8 both
    r56 07.2 up 08.2 down



    opamp2

    1 05.8
    2 00.4
    3 00.4
    4 07.2
    5 03.8
    6 03.7
    7 03.8
    8 03.7
    9 03.7
    10 03.7
    11 0
    12 03.7
    13 03.8
    14 03.8



    ac1 + 07.2 - 0
    ac22 + 05.0 - 0

    c3 0 up 03.8 down
    c4 03.8 right 0 left
    c8 05.0 right 0 left
    c27 0 both

    r3 0 both
    r10 0 right 03.8 left
    r11 0 both
    r34 0 both
    r35 0 both
    r36 03.8 both
    r39 03.8 BOTH
    r40 03.8 up 02.4 down
    r41 03.8 up 0 down
    r43 03.8 BOTH
    r45 03.8 up 08.2 down
    r46 03.8 BOTH
    r49 03.8 right 0 left
    r50 0 up 03.8 down

    L1 05.0 BOTH


    IC3


    1 03.7
    2 03.7
    3 05.0
    4 05.0
    5 00.2
    6 0
    7 0
    8 0
    9 0
    10 05.0
    11 00.3
    12 05.0
    13 0
    14 05.0
    15 0
    16 00.5
    17 0
    18 0
    19 0
    20 03.8


    power regulators 3 prong

    q3 switch on E 05.0 c 05.0 B 04.3 fluctuates between 4.2,4.3,4.4
    switch off E 05.5 C 0 B 05.0
    q4 switch on E 09.2 C 09.2 B 08.5
    switch off E 09.4 C 0 B 08.7

    Ic2 in 09.2 out 08.2
    Ic5 in 09.2 out 05.0
    Ic6 in 09.2 out 05.0


    ------------results--------------------
    faulty neo cd



    op amp 2

    1 05.6

    4 06.9
    5 03.4
    6 03.4
    7 03.4
    8 03.2
    9 03.2
    10 03.2

    13 03.6
    14 03.6


    Ic1

    5 01.1


    Ic3

    11 00.7

    20 02.1


    cxa Ic4

    10 04.4

    15 00.8
    16 00.8

    19 00.8
    20 00.7
    21 00.7
    22 00.7
    23 00.7
    24 0

    Ic2 out fluctuates between 07.9 and 08.0
    Ic6 out 05.0

    ac23 + 04.8
    ac2 + 07.3/07.2
    ac1 + 07.0

    flipped board switch is on left

    ac10 + 00.7
    ac11 + 00.7 - 00.5
    ac12 + 00.7 - 0
    ac19 + 00.8 - 0
    ac13 + 00.8 - fluctuates between 00.3 and 00.5
    ac8 + 00.8 -this one kind fluctuates too from 00.6 to 00.8


    L 4 is the culprit connected directly to pin 18 or 19 of the cxa
    Last edited by jetblue; 01-16-2013 at 05:41 PM.


    I made the impossible possible,i fixed gradius sega cd!

  2. #2
    3t3rn@l n00b
    Mugicha's Avatar
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    you are awesome jetter. good job you and thesteve!
    Quote Originally Posted by cdamm View Post
    we barely even talk about neo here.

  3. #3

  4. #4
    Axel's Trainer
    SNKNostalgia's Avatar
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    Good ole thesteve knows his stuff. He did wonders for my faulty Duo I bought new 12 years ago and casually played until the past few years due to owning a lot more games. Those caps just go out on black Duo systems no matter what. I can't stress it enough to change caps on them, even if they work fine.
    God made dirt, and dirt bust yo ass!


  5. #5
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    hey guys, i've got a neo geo cd with the same problem: black screen, no sound. i opened it and found that the diode D7 was broken.
    Neocda31.jpg
    so i bridged it and got the boot-sound on start-up, but the screen is still black.
    does anybody know the technical designation of the diode?
    it seems to be the same as the diodes D4 and D5 on the power supply part, but on the schematic they're designated just as DIODE.
    Neo-cda3-1.png
    thanks in advance

  6. #6

  7. #7
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    the diode doesn't have any markings, as you can see on the diode D5
    20130701_092534.jpg

  8. #8
    JammaNationX
    Xian Xi's Avatar
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    Looks like a 200mA diode. If you remove it from the board there should be marking on the under side of the diode. You may need a mag glass to see it on the small ones.

  9. #9
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    no markings under the diode either

  10. #10

  11. #11
    Lazy SNK Employee
    ROM-Lover's Avatar
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    Hi, my NEO-CD has shown the same issue of playing blind.
    After studying your log it was easy for me to figure out it was the L5 coil.
    I ripped a similar part of a not working MV-1F connector and brought it back to live.
    Ive printed your post to keep it in for future projects. Maybe itll be helpful for the repair of a famicom clone console with the same symtoms.
    Thank you very much and keep on your great work and sharing it.
    Last edited by ROM-Lover; 05-30-2019 at 05:55 PM.
    Twinkle Star till i die!

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