I wonder if anyone can assist me in diagnosing a sound problem I have with my PCE Duo console.

Basically I've noticed that for CD based games certain sound effects are so quiet they are almost impossible to hear. For example:

Tenchi wo Kurau: The voices are all missing (even when playing with them turned on)
Chiki Chiki Boys: All sound effects are almost mute (bar the coin pickup sound strangely)
Dracula X: Certain sound effects like the "getting hit", "window shattering" and the little speech the Grim Reaper gives at the start of the game are all missing. Weirdly the fully voiced intro is still perfectly ok.

The music for all these games play perfectly fine. As mentioned above I can hear the sound effects, but they are so quiet they almost always get drowned out by the CD soundtrack.

Hu Card games all seem ok. For example Street Fighter 2 sounds perfect - with all the music, sound effects and voices all perfectly intact so I believe this issue is most likely isolated to CD games only.

Secondly I had the capacitors replaced on my PC Engine just this week as I was aware of this issue for a little while. I was hoping replacing the capacitors would have fixed things but clearly the issue is ongoing.

Any tips/advice on what might be causing this issue? I've tested the console on two TV's and the problem is present on both, and also tried the games on the PC Emulator "Magic Engine" and the sound issues aren't present there so I believe its a console based issue.