Questions about MV-1F I just got

I just got an MV-1F to go with a SuperNova. Two of the first four times I booted it, I got a "Z80 error" message. This happened one time each with a barely used SVC Chaos cart (purchased from Trieu) and an excellent condition Bust-A-Move cart. I never had a problem with either of these in my consolized MV-2F. I have since rebooted it about a dozen times, with SVC, BAM, and Waku Waku 7, with no further problems. Also, the audio went out a couple of times (I have it set to mono, since the audio is going through the JAMMA harness). I think this was due to a loose or dirty contact with the harness, and it has worked fine for the past couple of hours. Could both of these problems be related to dirty contacts? I am cleaning both the cart and JAMMA contacts. Some of the copper(?) on the JAMMA contacts is worn off.

Also, I'm not sure what type of BIOS (US, Jpn, Euro) I have. In Bust-A-Move, the "Puzzle Bobble" intro screen comes up, while the "Bust-A-Move" intro came up in US mode with Unibios on the MV-2F. However, I get English text in SVC Chaos in the character dialogue, while I remember getting Japanese text in Jpn mode of the Unibios. Do I have a Euro BIOS, or a different version of a US BIOS, maybe? How can I tell?

TIA for any assistance.

Intermittent Z80 errors can occur with an intermittent connection between the Z80, 68000, YM2610, even poor connection with the SLOT 1F cart socket sub board. Make sure the plug socket connections here are clean between the sub board and mobo. There is a watchdog on the z80 that reports any unexpected interupts to the main 68000 processor afaik, this will give the error message, sometimes the sound just mutes.
The MV-1F is a 3 layer board, it may look like there are no dry joints around this stage, but it may be worth reflowing each pin, including the SM1 rom and 6116 ram. I have experienced this problem and after doing that the problem seemed to clear.