Vintage Synth Repair

The unit arrived with missing screws in the case. 
Always a bad sign.

The service manual, kindly given to me (also the one on the web), is only 71 pages and really only goes through the tests.

My DX7 and TQ5 service manual are much more detailed.
Were these synths just 'swap the board" type devices?

Anyway the test stops at the self test with a message "* M3 IRQ CHECK ERROR. TEST ABORTED *" and you can't go on to the other tests.
The service manual only say "If Test B" the M3 test " is NG" no good "then the error may be related to one of the M3 IC's IRQ levels"
What does that mean??

The 2 M3 chips YM7119 are on the DM2 board have something to do with the Wave ROMs.
Is this test trying to read all the Wave ROMs and failing?
Is the CPU just timing out because the M3 isn't returning soon enough?
It's the interupt request part I don't get.

Anyone with any more info about this chip?
Anyone had this problem and managed to get past the IRQ test ?

I can get a few weird notes out but it sounds like misaddressing of the Wave ROMs and locks up fairly quickly. 

Thanks for the help
Royce