- Joined
- Apr 3, 2011
- Posts
- 5,850
I've got quite the basket case of an MV-1F, typical eBay purchase sold as not working.
In short, the system is so dead it doesn't even have the click of death, it is stuck at the point before that, before the video sync signal is even set correctly. My test CRT doesn't like the signal so it always goes back to a blue screen.
When I first got this board, the SM1 ROM and 2K SRAM for the Z80 had been socketed by someone in the past (that 2K SRAM looks to be a 16K one, when I have a replacement 2K SRAM I'll swap it). The NEO-C1 looked to have been resoldered. The battery itself had been replaced at some point. The traces around the battery have a bit of corrosion here and there but honestly this is not bad for a junk board.
Given the deadness of the board, I figured start with the core of the system, so swap the System ROM to another one, no change. I did try another 24Mhz oscillator, no change. With logic probe I noticed the 68K CPU, System ROM and RAMs had basically no bus activity, so I figured don't have much to lose so I desoldered the 68K, put a socket in and tried another 68HC000 CPU, no change.
Beyond that, aside from replacing SRAM chips and fixing the odd possibly suspect trace I can see, I am not sure what the cause of death is here. I am fully expecting one or more of the custom chips to be bad, like the LSPC or NEO-B1, NEO-C1, NEO-I0 or something. Still I hope in the back of my mind this board can be saved, it is overall in way better shape than most junk MV-1F boards I've seen.
So my main question is, what can cause an MVS board to be so dead it can't get to the click of death? aka the 68K is running code but it keeps crashing over and over again and the watchdog circuit is resetting it every time.
In short, the system is so dead it doesn't even have the click of death, it is stuck at the point before that, before the video sync signal is even set correctly. My test CRT doesn't like the signal so it always goes back to a blue screen.
When I first got this board, the SM1 ROM and 2K SRAM for the Z80 had been socketed by someone in the past (that 2K SRAM looks to be a 16K one, when I have a replacement 2K SRAM I'll swap it). The NEO-C1 looked to have been resoldered. The battery itself had been replaced at some point. The traces around the battery have a bit of corrosion here and there but honestly this is not bad for a junk board.
Given the deadness of the board, I figured start with the core of the system, so swap the System ROM to another one, no change. I did try another 24Mhz oscillator, no change. With logic probe I noticed the 68K CPU, System ROM and RAMs had basically no bus activity, so I figured don't have much to lose so I desoldered the 68K, put a socket in and tried another 68HC000 CPU, no change.
Beyond that, aside from replacing SRAM chips and fixing the odd possibly suspect trace I can see, I am not sure what the cause of death is here. I am fully expecting one or more of the custom chips to be bad, like the LSPC or NEO-B1, NEO-C1, NEO-I0 or something. Still I hope in the back of my mind this board can be saved, it is overall in way better shape than most junk MV-1F boards I've seen.
So my main question is, what can cause an MVS board to be so dead it can't get to the click of death? aka the 68K is running code but it keeps crashing over and over again and the watchdog circuit is resetting it every time.
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