neo geo cd black screen

jetblue

Crossed Swords Squire
Joined
May 6, 2006
Posts
185
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:

neo2_zpsa5f300d7.jpg


other side:

neo1_zpsad5bd78e.jpg


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 :emb:


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:

Mugicha

3t3rn@l n00b,
10 Year Member
Joined
Aug 23, 2011
Posts
3,510
you are awesome jetter. good job you and thesteve!
 

SNKNostalgia

Avid Neo-Expert
Joined
Jul 11, 2005
Posts
1,982
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.
 

saddam

n00b
Joined
Jun 21, 2013
Posts
3
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
 

Xian Xi

JammaNationX,
15 Year Member
Joined
Dec 1, 2005
Posts
27,748
Never bridge a diode. It's a diode for a reason. Remove the bridge and buy a replacement diode. Read the markings on the diode.
 

Xian Xi

JammaNationX,
15 Year Member
Joined
Dec 1, 2005
Posts
27,748
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.
 

ROM-Lover

New Challenger
Joined
Mar 11, 2008
Posts
53
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.
I‘ve printed your post to keep it in for future projects. Maybe it‘ll 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:

Tengugurl

Cheng's Errand Boy
Joined
Feb 9, 2017
Posts
111
Hi all! I am having a similar issue.
Wish I could see true L4 pics. Does anyone have a photo of this area? I want to check the pins that’s near the Cx and do a quick multimeter check to see if I have similar symptoms (5v one side and 0 the other)

Thanks all!
@jetblue or
@ROM-Lover

!! Think I figured it out :) - I am going to Replace mine soon and try bridging it soon.
Is this it?
 

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Last edited:

ladyxyuna

n00b
Joined
May 6, 2023
Posts
6
Olá pessoal, tenho um cd neo geo com o mesmo problema: tela preta, sem som. abri e descobri que o diodo D7 estava quebrado.
View attachment 1665
então fiz a ponte e obtive o som de inicialização na inicialização, mas a tela ainda está preta.
Alguém sabe a designação técnica do diodo?
parece ser o mesmo que os diodos D4 e D5 na parte da fonte de alimentação, mas no esquema eles são designados apenas como DIODO.
View attachment 1666
desde já, obrigado
My board is exactly the same like yours. However I replaced all inductors. And it is still not working
 
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