Here is a quick and dirty drawing of fm audio pre-amplification part from an ACE I/O board : Model K5710DE

Its' not finished yet : some signals to/from OPM are missing, adpcm mixer is not here and this drawing stop to the output connector located on the back (We will refer this connector as AO). Please, note also that transistors are DTC114 (NPN with built-in resistors), my symbol representation is wrong.
Components values may also differ from a Compact, as well as references names. But I'm pretty sure implementation is the same. So any value/names equivalent from Compact are welcomed.

Anyway, the important part is fully here !

Now, testing while fixing sound issues should be done using this AO connector, as it seems to be the closest to the YM3012.

If the problem does not come from the PSU (correct +12v and -12v rails) or opamps or broken traces, it should be located somewhere around here : DAC amplification (the part at the right of YM3012), and channels preamplifications. Relevant components : all ceramic precisions caps (C41, C28 and C29) ! These are rated at the lowest possible tolerance (B = ± 0.1 pF), this is really important.

Also, Q4 an Q5 may be removed for testing purposes (AND ONLY FOR TESTING !) with the use of AO connector. If the sound is correct then, these transistors may be dead, or the diode D7 could be shorted.


A word about the design : it seems to be a typical implementation of YM2151 and YM3012. I would like to try some improvment by changing both opamps with something some dedicated to audio amplification (like a TL074, or NJM2059). Changing C41, C28 and C29 by polystyrene type capacitors could also be a good idea.