I have a MV1FZ and I'm getting the following error: YM2610 TIMER TIMING (FLAG).
It has no sound aside from a loud static buzz sound.
I tried swapping the ym2610 with another one but the error and the problem persist.
I would check that connectivity between the Z80 and YM2610 as well as the clock going into the YM2610
wiki.neogeodev.org
In the lower left of the pinout, SDD1 to SDD8 should connect to the data pins of the Z80. Then if you follow the dotted line to the top left, those 6 pins. I believe A0-A1 and IRQ should go to directly to the Z80, while the remaining should go to the NEO-D0 right below the Z80.
For what the error means. The YM2610 has timers you can setup. When a timer is up you can have it generate an IRQ or set a flag in one of the registers. The test setups a timer for the flag method, then waits a little while and checks if the flag is set. If the flag is not set then it will generate the error you are getting.