Watchdog when cart slots plugged in?

avramce

Kabuki Klasher
Joined
Sep 24, 2019
Posts
125
Hi all, received a pretty clean 4-slot, but noticed that it was watchdogging on boot.

I took the board apart, and saw that I get crosshatch when I boot it with the stock BIOS with the daughter board off, and get the service menu if I boot it using UniBios with the daughterboard off.

I ran Neo Diag on the board, and all tests came back clean, but all three BIOS chips return a watchdog when I attach the top board.

At this point, I have the new cart board, and two known working cart boards, but all three of them will watchdog if attached.

Any thoughts on what to trouble shoot next? I don't see any bent pins on the connectors for the daughter board.

http://imgur.com/a/yiwSEWH
 

shadowkn55

Genbu's Turtle Keeper
15 Year Member
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Dec 9, 2006
Posts
2,386
Being stuck on the scrambled green screen is usually related to the calendar. A watchdog problem is a constant reset.
 

avramce

Kabuki Klasher
Joined
Sep 24, 2019
Posts
125
Hmm, my bad for the terminology, in this case, yes, it is a solid screen. I removed the battery on board and saw no corrosion, and performed a backup ram wipe, anything else I can try to resolve the problem?
 

HeavyMachineGoob

My poontang misses Lenn Yang's wang
10 Year Member
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Apr 3, 2011
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5,790
The watchdog reset is from the CPU crashing and auto-resetting. Something is causing the CPU to crash repeatedly. The common area to check for problems is the CPU, Work/Backup RAM and BIOS chips and the traces between them.

Beyond that, the P ROM chips on the cartridge, the PROG board slots and related logic that connects all that to the CPU could potentially crash the CPU if something is wrong. It could be a bad logic chip somewhere on the top board, or a broken trace. I assume you've never had a game actually boot properly on this 4-slot?
 

ack

Ninja Combat Warrior
15 Year Member
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Apr 9, 2009
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537
Solid screen can also be caused by the 5V rail being to low.
 

avramce

Kabuki Klasher
Joined
Sep 24, 2019
Posts
125
Ack nailed it - I had a Supergun with a simple 5V PSU instead of a proper arcade PSU. I swapped it out with a PSU with a voltimeter and dialed it in to 5.05V when powered, and everything is working swimmingly now.

Oddly enough, I used the setup I had the problem with to test a MV4T3 with no issue. I guess the MVH-MV4 has a higher power draw?
 

shadowkn55

Genbu's Turtle Keeper
15 Year Member
Joined
Dec 9, 2006
Posts
2,386
The MV4 has a lot of discrete logic chips used for switching the lines between the cartridges. The smaller boards like the MV4F managed to cut down on the chip count and the power draw by consolidating many of them into ASICs.
 
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