Dead D4990?

HMG

H = Heinously, M = Massive, G = Gonad,
I've got an MV-1T with a seemingly unfixable calendar error. Sometimes it shows a stuck green screen, other times it shows a black screen with "calendar error". I've already checked for +5v on the D4990 (which is present), replaced the oscillator a couple of times, reflowed the ceramic caps and even the D4990, but I still can't get to crosshatch or a game. The chip is kind of corroded, is it possible it needs to be replaced?
 

smkdan

Galford's Armourer
The calendar I/O goes through the NEO-F0 (see wiki pinout for specifics) so there may be an issue in that area too. Alternatively, you can try burning a diagnostic BIOS, hold ABCD on power on and go to calendar I/O test. It will show you the pin states in real time which may help us figure it out.
 

HMG

H = Heinously, M = Massive, G = Gonad,
Rise from your grave.

Decided to take another crack at this MV-1T. This time I did some comparing against a good MV-1 (well, it has issues of its own, but it can boot to crosshatch).

The only thing of significance I found was D4990 pin 4 was not connected to NEO-F0 pin 5, patched that. Still stuck on green. I then did some logic probing, nearly all pins seem good, except 12 and 13. Both were low, oscillator was new. I swapped 4 other 32.768Khz oscillators, they all are high on pin 12, low on pin 13.

Are all my oscillators bad? Is my D4990 bad? It seems like only the oscillator is holding the board back from booting now.
 

yavuzg

Timid Neo Newbie
Rise from your grave.
Are all my oscillators bad? Is my D4990 bad? It seems like only the oscillator is holding the board back from booting now.

no, you simply cannot get a reading directly at crystal legs (which are directly connected to 12-13 of D4990) with an ordinary logic probe. you "may" hear some signal for a very short time with "some" logic probes. only with an oscilloscope you can...
 

HMG

H = Heinously, M = Massive, G = Gonad,
no, you simply cannot get a reading directly at crystal legs (which are directly connected to 12-13 of D4990) with an ordinary logic probe. you "may" hear some signal for a very short time with "some" logic probes. only with an oscilloscope you can...

I know, I was going by a repair log by channelmaniac. He checked a known working board and pins 12-13 showed high.

Did you burn a Diagnostic bios?

If someone can tell me whether the Neo Geo BIOS (cart ROMs too) have to be byteswapped or not, I will burn one. I even made a thread, never got an answer.

D4990 die easily. Try to swap.

Ugh, really? Man that sucks, I already bought a new one for this board.
 
Top