mv1A watchdog clicking noise with garbage screen

babeloued

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Joined
Sep 27, 2015
Posts
52
hi
i have a problem with my slot MV1A who have stay on watchdog and clicking noise with garbage screen
i check all connections with sp1 eprom and 68k
,change work ram,backup ram and video ram but stay with the problem,i change the 2 PAL snk1 et snk2 and sfix rom,put a good smkdan diagnostic eprom ,but still on watchdog.
please help me another way to solve that problem
thanks:rolleyes::rolleyes::rolleyes:
 

GadgetUK

Ace Ghost Pilot
Joined
Sep 27, 2013
Posts
1,323
hi
i have a problem with my slot MV1A who have stay on watchdog and clicking noise with garbage screen
i check all connections with sp1 eprom and 68k
,change work ram,backup ram and video ram but stay with the problem,i change the 2 PAL snk1 et snk2 and sfix rom,put a good smkdan diagnostic eprom ,but still on watchdog.
please help me another way to solve that problem
thanks:rolleyes::rolleyes::rolleyes:

Probably one or more faulty Neo-Buf chips. I've done a number of videos on these recently and came across only faulty Neo-Buf chips causing a watchdog when trying to diagnose with the SMK diag ROM.
 

babeloued

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Joined
Sep 27, 2015
Posts
52
thanks to help me
i will check all neo buf
i can say you the 68k is ok because i test it to another board
 

babeloued

New Challenger
Joined
Sep 27, 2015
Posts
52
hi
i check all 5 neo buf and try them to another slot,there all right,all are good
another way to solve it?????
thanks
 
Last edited:

GadgetUK

Ace Ghost Pilot
Joined
Sep 27, 2013
Posts
1,323
That's a surprise lol! That said, there are always lots more possible causes. Are you sure the CPU has good connectivity to the ROM and RAM? That type of failure could be ROM (you ruled that out with the diag ROM), RAM, 74HC259 (maybe), maybe the GRC (I think it has databus connectivity), maybe the 74HC32 connected to the RAM. It could also be that the OE of the ROM is not being driven correctly due to a bad MGA? (assuming that handles it on the 1A). The F0 connects to the databus too I think. I am sure there are many more causes beyond those too. I would be booting this without any neo buf chips (if you still have them removed) - just incase one of them is being enabled when it shouldnt be. So whilst they seem to work on another board, testing without any of them could provide different behaviour. If it did, you then need to look at the OE signals on each to see which is being enabled when it shouldn't.
 

babeloued

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Sep 27, 2015
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hello
cpu connectivity to rom and ram is good ,i m sure
i will check next day 74h259 and 74hc32
thanks
 

babeloued

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Joined
Sep 27, 2015
Posts
52
hi
i always test my motherboards with smkdan eprom
74hc259 and 74hc32 are good
bios SM1 and bios 000-LO are corrupt,i change the 2 bios but same problems,so all neo buf are remove to the motherboard and i realise after click of death and screen garbage about 2 seconds ,the board want to boot so the screen is green or blue or black or red uniform with any text and again garbage with click noise,so i think it is better than last day
can you help me for the next step you will go...
thanks GadgetUK for your precious help
 
Last edited:

babeloued

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Joined
Sep 27, 2015
Posts
52
hello everybody
today,i work hard to repair my mv1a slot
so i program the 2 pal snkA snkB with a gal 20v8b and great i have again screen come back with smkdan test,so the 2 original PAL are bad
but still another problem,smkdan confirm a problem with :bram unwritable lower,so i change with 2 new rams the 2 backup ram and 74hc32 but it is the same problem
do you have and idea ,is it a problem connection between 74hc32 ,backup rams????
this are the level on pin of 74hc32 U4 near backup ram
1 H
2 H
3 H
4 H
5 H
6 H
7 GND
8 H
9 H
10 L
11 H
12 H
13 H
14 VCC

thanks for your precious help
 
Last edited:

babeloued

New Challenger
Joined
Sep 27, 2015
Posts
52
bingo:multi_co::multi_co::multi_co:
i resolve my problem
about the bram unwritable lower so i change hc259 next 7404 and all test passed with smkdan diagnostic eprom,but when i change with original bios so i have a beautiful screen with text say me :Z80 ERROR.i change z80 ic resolve it but another error say me calendar error,i change the nec ic D4990 and now i have a beautiful crosswatch so i insert a game and every sound and text are ok,i can play now.
thanks you very much for your help GADGET UK,you do a good work,i will become with another board repair a few days
as tala vista,i will be back for another repair
 
Last edited:

BIG BEAR

SHOCKbox Developer,
20 Year Member
Joined
Dec 14, 2001
Posts
8,230
What programmer did you use to burn the GAL chips if you don't mind me asking. I'm in need of a new programmer as the ones I own have a lot of mileage.I'm fighting to get one in particular to cooperate.
thank you
BB
hello everybody
today,i work hard to repair my mv1a slot
so i program the 2 pal snkA snkB with a gal 20v8b and great i have again screen come back with smkdan test,so the 2 original PAL are bad
but
 
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