[solved] Problem with right audio channel of a sega naomi 2

[Orakelschaf]

Hello,

i hope someone here can point me in the right direction with the (right channel) audio problem of my sega naomi 2:

Problem

• within the test menu -> sound tests i turn left and right speaker to ON
• left speaker outputs sound
• right speaker does NOT output sound (the problem!)
• video and gaming works 100% perfect, but right audio channel is missing

Things i tried so far

• Checked if there is a jumper or setup config for mono/stereo stereo. Have found none.
• Checked jumper setting with another working noami2: matches
• Replaced Filter board: No change. It is not the filter board.
• Checked cables: It is not the cables.
• Power supply provides enough voltage.
• Replaced IC 39. No change
• Complete recap if the board and the filter board.
• Visuell Inspection of blown parts/missing traces : None

NEC C844G (IC39)

I replaced and measured the NEC 844G (IC39):

• Pin 01 (Out1): 5V - Shows Sinus wave if left channel is active
• Pin 02 (Ii1): 2.6V
• Pin 03 (IN1): 5V
• Pin 04 (V+): 12.2V
• Pin 05 (IN2): 5V
• Pin 06 (Ii2): 2.6V
• Pin 07 (Out2): 5V - Does NOT show sinus wave if right channel is active
  
• Pin 14 (Out4): 5V - Does NOT show sinus wave if right channel is active
• Pin 13 (Ii4): 5V (shouldn't this be 2.6V? maybe there is an issue?)
• Pin 12 (Ii4): 5V
• Pin 11 (V-): 0V
• Pin 10 (IN3): 5V
• Pin 09 (Ii3): 2.6V
• Pin 08 (Out3): 5V - Shows sinus wave if left channel is active

It looks like either a component which feeds the right channel to the NEC C844G is blown, or there is really a "mono" setting. Does anybody know what feeds the NEC C844G and what else i can test/replace.

Thanks alot!

 

[Orakelschaf]

Does anyone have some information to this topic or any idea how i can trace the issue?

Did someone of you ever desolder all components of a naomi2 pcb to be able to trace issue? (if so the photos of the clean pcb would help )

 

[Orakelschaf]

My Issue is solved. Today i traced the L/R audio from the amp to the DAC (PCM 1725U on IC36). Replaced the DAC and both audio channels are working again.

I will -maybe- add some photos of my traces later to help others

Preview: