- Joined
- Apr 3, 2011
- Posts
- 5,850
Hmm, okay. Simple enough I guess. I don't have a logic probe or oscillator, nor would I immediately know how to use one. I'm horrible at desoldering SMD ICs too, so I think I'll just pack this MV-1 away in it's box again. But I'm happy I did all this, at least I have a much better idea what's wrong with it. Considering how big this board is, I don't think it'd be worth anyone's time or money to buy this thing for parts. Perhaps my skill and toolset will improve enough down the road to facilitate fixing this PCB. Again, thanks for all the help everyone, you guys are awesome!
On a similar note, I found this post amongst Channelmaniac's repair logs. Boy, there sure is a lot that can cause the click of death.
On a similar note, I found this post amongst Channelmaniac's repair logs. Boy, there sure is a lot that can cause the click of death.
channelmaniac said:Model: MVS MV-4F
Symptom: Stuck in Watchdog (Click of Death)
Have a 4 slot board in to repair that was giving the click of death - stuck in watchdog - problem.
This can be caused by many different problems, including:
Bad CPU
Bad Work SRAM
Bad Backup SRAM
Missing control signals on Work or Backup SRAM
Shorted 74AS245 ICs buffering program ROMs on top board to CPU on bottom
Short on address bus
Short on data bus
Missing address or data signals to chips
First thing... Check for gouged traces. Found and fixed one. No effect.
Next... Substitute BIOS. Nothing.
Next... Check control signals on the Work RAM - Stuck high on pins 22 and 27.
Next... Check control signals on the Backup RAM - Stuck high on pins 22 and 27.
Next... Check control signals on the BIOS ROM - These were working.
So we had a problem somewhere in the system to where it was trying to read the BIOS but not able to initialize hardware.
Pulled the 74AS245 ICs buffering the data lines to the top board. Had no effect.
Checked for more broken traces. No more were found.
Checked the address and data lines going to the BIOS and SRAM ICs. All were good. Checked the data lines going to the NEO B1 chip. All were good. Checked the data lines. All were good.
Next checked the A22* and A23* alternate lines. Missing one one! Ran a jumper wire from Pin 55 of the NEO-E0 IC to pin 117 of the NEO-B1 IC and the board came up!
OOPS. Z80 Error. Reset line stuck high. On a Z80 since the reset line did not transition from low to high the Z80 never booted. Ran a jumper and the audio section worked. Replaced the pulled 74AS245 ICs and the board wouldnt' boot. Reset was stuck low.
Turns out the reset line for the Z80 CPU and chips on the left side of the board goes through the 74AS245 IC at E11. Removed the jumper for the reset line and board booted normally.
Plugged the top board back in, inserted some test carts and played a couple of games.