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daifuku74

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Hello everyone. I have this machine trolling me for a few weeks now and I definitely need advice please. 😢
It starts with glitched video and occasional noise before "stabilizing" and showing the neo geo logo and booting games.
Game either boots fine or the text is incorrectly displayed (and that does it also on the neo geo intro logo when it happens), letters are kind of incomplete.
Here is an example of the problem. The video shows when text is bad.

View: https://youtu.be/qjrtxJY_82g

I only have one game cartridge for testing. I've taken it apart and cleaned it completely. It was not dirty or worn out in any way.

Here is what I've tried so far:
Tried with original bios with no cartridge inserted.
I had dark blue screen most of the time after the glitched video, rarely green, and red once or twice.

tried with a known good power supply 9V 2A negative center
tried with a brand new quality shielded video cable
problem still the same.

suspected the bios so I removed the original BIOS, put some round pin IC sockets and installed an Unibios 4 that I programmed myself.
problem is still the same.
I can sometimes see during the glitched video a brief green screen with EXCEPTION ERROR HANDLING, but I can never have the display stable enough to read the details at this point. It's a pity because that would maybe help.

I tried also the smkdan diagnostic bios.
It reports "all tests" passed.

I tried LOTS of continuity tests, between the main elements (bios, 5814 chips etc). Thanks to that very forum and the kindness of its members, I found many lists with all the corresponding pins to tests. No problem in traces detected.
I also tested continuity in all signals that go between LSPC2-A2 and NEO-B1, here again, no bad trace detected.

I put the 5814 chips also on round pin IC sockets.
I replaced the rest line capacitor with a new one, and also the main power filter one.
I also replaced 3 or 4 ceramic caps that looked dirty on their pin, but still the same.
I reflowed pretty much everything, bios pins, one 74HC04, LS254 (these two chips report fine in the eeprom burner running logic tests)
LSPC2-A2, NEO-B1, NEO-D0, NEO-E0, NEO-C1, NEO-GO, all CX chips, all cart slot pins, AV port and etc

When doing voltage tests, I found a place that seems to make the glitch go away when touched with a meter probe or screwdriver.
It is the red zone in the schematics below. That C54 has been replaced already, and there is no bad trace from there. Resistors around are reporting good values.
I do not need to push down, just touch the cap pin, and it makes the video "stabilize", and I can see the unibios white screen with no cartridge.

I do not understand why, but it may be a clue for more experienced troubleshooters.

I also need to mention this board is quite curved. The pins of the cartridge slot are soldered closest to the board on the left and right edges,
and with more distance in the middle. It is this way from the factory for sure, and used to work with no issues.

If you have any clue, I'd be glad. I hope this machine can be revived fully. Thanks for your time and input.

aes35meter.png
 

ivan.caregnato

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have you completely replaced all caps, 2200uf included? In my case, that was the cause of some graphical issues. I've replaced it with a low ESR ELNA SILMIC II audio capacitor. RGB bypass also could help: visit JNX website for a guide...keep in mind that this mod cuts off the composite signal
 

daifuku74

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2200uf has been replaced, along with the 10uf for the reset line. A full capkit may be necessary in the end. I have just read that the low ESR ELNA SILMIC II make a real difference sound wise, and also that replaced caps should be soldered on both sides of the board. The caps I replaced for now are not ultra quality ones, but should be enough to test is there is improvement I guess.
 

ivan.caregnato

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Mine, like other caps, is soldered only on the bottom side of the board. It makes easier to remove them for future recap. you could try with a RGB bypass if you only need RGB signal...it's the quickest way to try to solve your problem and it's reversible
 

daifuku74

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This board already has a clean enough RGB, but yes I could try as it removes the need of some of the 470uf caps. I remember some topics here and there of unexpected things when performing this mod (image position or other glitches), so I hope I can revert if problems start to pile up
 

ivan.caregnato

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my 3-5 with RGB bypass (the JNX way, not that one describes on RetroRGB) doesn't have any issues (until now...fingers crossing)
The glitches with multicart happen sometimes but when games start (also this happens with NeoSD), everything seems fine
 

daifuku74

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my 3-5 with RGB bypass (the JNX way, not that one describes on RetroRGB) doesn't have any issues (until now...fingers crossing)
The glitches with multicart happen sometimes but when games start (also this happens with NeoSD), everything seems fine

Do you have a link explaining the JNX way please?
Also shouldn't I be concerned with the exception error handling before changing things any further?
 

ggallegos1

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Potentially dumb question, are you sure you have no cold solder joints or bridges in that area? If you're fixing the issue by touching it with a screwdriver, it sounds like a circuit issue
 

daifuku74

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At this point, no suggestion is dumb.
I can't find cold solder joints or anything in this area nor anywhere.
Also the continuity is good from this mysterious pin.
I can't understand why bridging this cap leg with air improves the situation.
I circled the cap leg in red on both sides on images below. This cap is new. With the old one it was the same.
On the picture it seems there is dirt below NEO-D0 but this is only a reflectionof light in the picture, the board is clean.
On the reverse side, some little flux remains near the circle, but it's okay.
There are also little lighter green dots, these appear on the PCB when using hot air.

up.png

down.png
 

daifuku74

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On the line of this 30pf is another 6pf, then it goes to 74HC04 and then on the other side it's the oscillator.
Other sources have suggested replacing the crystal. Thing is I cannot find an exact match. There are 24.000 Mhz available but this one is 24.16782
so I'm not sure if I can go ahead and swap it for a 24.0
 

Nic034

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have you completely replaced all caps, 2200uf included? In my case, that was the cause of some graphical issues. I've replaced it with a low ESR ELNA SILMIC II audio capacitor. RGB bypass also could help: visit JNX website for a guide...keep in mind that this mod cuts off the composite signal
Great choice !
 

ShootTheCore

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On the line of this 30pf is another 6pf, then it goes to 74HC04 and then on the other side it's the oscillator.
Other sources have suggested replacing the crystal. Thing is I cannot find an exact match. There are 24.000 Mhz available but this one is 24.16782
so I'm not sure if I can go ahead and swap it for a 24.0

DigiKey sells programmable clock crystals - tell them the speed you want it clocked to, and they'll set it before they ship it to you.
 

daifuku74

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have you completely replaced all caps, 2200uf included? In my case, that was the cause of some graphical issues. I've replaced it with a low ESR ELNA SILMIC II audio capacitor. RGB bypass also could help: visit JNX website for a guide...keep in mind that this mod cuts off the composite signal
Ivan please, what was the kind of graphical issue you had that was repaired by the complete cap replacement? Do you have a picture example or a precise description? Thank you
 

ivan.caregnato

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I had a strange issue that makes my CRT screen flash sometime during my gameplays (like an increased brightness level that lasts and few ms). It was very annoying. Everything was fine on my OSSC.
 
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