MV1FS click of death, but diag bios all OK?

I recently received an MVS MV1FS 'cartridge holder' (great term used by the auction seller) in non-working state, the battery started a little bit of corrosion but the board itself is in pretty good condition. I've tested most of the points around the battery area and haven't found anything amiss.

The symptoms are:

With stock bios, slow click of death reset, with following graphics showing:

With unibios, fast click of death reset, no graphics displayed.

With diag bios, all tests pass, including Z80.


I set all dips to ON for the work ram test, which I guess works, it shows the text and sits there. I left it for a couple of minutes, but it hasn't fixed the booting issue.

I've also tried shorting the J2 to bypass the watchdog, but the board doesn't progress past the aforementioned states, it just doesn't reset any more.

Any help appreciated! The diag bios OK really throws me

Are you sure the unibios chip is OK?

GadgetUK said:

Are you sure the unibios chip is OK?

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It was taken from a working MVS board, so pretty sure, but I can check. I've also tested the stock bios in another board and that works fine too.

Did you remove the battery? If so, replace it and see if that helps.

I had a similar problem with my MV1FZ, and had to go to town on the connector with an eraser and a fiberglass pen and turn the volume pot down to get it working.

It might have been an intermittent issue I just randomly fixed, but it can't hurt to try.

Could it be a bad cap?

It could be an upper address line that the diag BIOS doesn't hit.

pulstar said:

Did you remove the battery? If so, replace it and see if that helps.

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I did. I can put a holder in with a cr2032 I guess to see if that helps.

DNSDies said:

I had a similar problem with my MV1FZ, and had to go to town on the connector with an eraser and a fiberglass pen and turn the volume pot down to get it working.

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The jamma connector you mean? I guess I will fiddle with the volume, easy enough to try, but hard to believe

Apocalypse said:

Could it be a bad cap?

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I can get a replacement set and try. There aren't that many outside of the audio section though, I think.

mikejmoffitt said:

It could be an upper address line that the diag BIOS doesn't hit.

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Hrm, any suggestions on what to test?


Thanks for the replies, guys

mikejmoffitt said:

It could be an upper address line that the diag BIOS doesn't hit.

Click to expand...

Where can you get that kind of info?
It would be most useful to know what are the limits and what is really tested.

fluxcore said:

Hrm, any suggestions on what to test?

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I would check address lines between the 68k and the RAMs.

Try a logic probe or oscilloscope and check all the address lines going to the BIOS, see if something looks funny. Good to check the control signals for it and 68k main RAM as well, and make sure calendar RAM is not misbehaving.

With the diag bios, run a WRAM test for at least 10 minutes. It will run a continuous loop.

Thread necro! Finally getting a chance to look at this board again.

I booted up the diag rom again, and if I hold ABCD to select tests, the calendar test doesn't work properly. Rather than perform a loop of tests, the first test counts down to 0 and then the board reboots. If I short J2 (disable watchdog reset), the board simply hangs instead of rebooting.

It seems to me like the watchdog never sees the data it's looking for and so reboots.

I left the WRAM test running for about 40 mins and it passed every check.

Things I've currently tried replacing, with no difference in behaviour:
BRAMs
4990
32kHz crystal
68k
74HC32 controlling backup

One weird thing about the diag bios is that if I boot up holding C+D it gives a z80 error, with or without the diag cart plugged in. Holding only D results in full z80 test passing, reliably.

My next thought is to try replace the NEO-B1...

I would check any transistors in the backup circuit.