Quantcast

Page 1 of 2 12 LastLast
Results 1 to 15 of 17

Thread: Very odd Mega CD Model 1 Sound issue (Sounds out of tune)

  1. #1
    Retro Nutter! Road Rasher Speedle's Avatar
    Join Date
    Mar 2009
    Location
    UK
    Age
    37
    Posts
    383
    Rep Power
    13

    Default Very odd Mega CD Model 1 Sound issue (Sounds out of tune)

    So turned on my Mega CD 1 today and straight away heard something wasn't right. At the Bios boot screen the music plays but sounds weird and out of tune..

    Games play fine and anything with CD audio sounds normal, but when I tried sensible soccer which has some via sections with what I'm guessing is not CD audio that sounds weird too...

    Here's a video of the boot screen;



    Sorry the audio is a bit low it's late and don't want to wake the misses

    I've spent loads of time searching the interwebs with no results matching my issue...

    Hoping the awesome peeps on Sega-16 can help me out.

    I've opened up the unit and cleaned all the contacts.

    My first thought is that some of the caps may need replacing, but I yield to the superior knowledge on the forum.

  2. #2
    Wildside Expert
    Join Date
    Feb 2015
    Posts
    125
    Rep Power
    5

    Default

    If the caps haven't been done before best to get them done they leak like a sift on these. have u looked on the motherboard for any signs? or trace damage?

  3. #3
    Retro Nutter! Road Rasher Speedle's Avatar
    Join Date
    Mar 2009
    Location
    UK
    Age
    37
    Posts
    383
    Rep Power
    13

    Default

    I couldn't see any leakage on the boards, but I've ordered new caps any way and will do a full cap replacement and report back my findings.

  4. #4
    Hedgehog-in-Training Hedgehog-in-TrainingSports Talker
    Join Date
    Sep 2015
    Posts
    37
    Rep Power
    0

    Default

    Well, I'll rule out caps right here. Yes, they tend to go bad after all those years, but they never cause glitches of these kinds.
    Bad caps will result in moving/rolling picture, quiet or dead audio, color problems.. All kinds of analogue misbehaviour.

    This problem is hard to nail down.
    I'd start tests by using a different Mega Drive, cleaning the MCD/MD connector, inspecting the mainboard for obvious problems.
    And if that doesn't produce anything, a better recording of the problem, please

  5. #5
    Retro Nutter! Road Rasher Speedle's Avatar
    Join Date
    Mar 2009
    Location
    UK
    Age
    37
    Posts
    383
    Rep Power
    13

    Default

    Tried all of the above, no change. Will post some better video in a few mins

  6. #6
    Retro Nutter! Road Rasher Speedle's Avatar
    Join Date
    Mar 2009
    Location
    UK
    Age
    37
    Posts
    383
    Rep Power
    13

    Default

    Ok some much better video evidence of the offending Mega CD who can't play a song in tune...

    https://www.dropbox.com/s/24qdp1o5q2...15720.mp4?dl=0

  7. #7
    Hedgehog-in-Training Hedgehog-in-TrainingWildside Expert
    Join Date
    Jun 2015
    Posts
    168
    Rep Power
    5

    Default

    Sounds like when you touch fuzzy in SMW2.

  8. #8
    Road Rasher
    Join Date
    Jul 2012
    Age
    40
    Posts
    423
    Rep Power
    10

    Default

    Quote Originally Posted by Speedle View Post
    Ok some much better video evidence of the offending Mega CD who can't play a song in tune...

    https://www.dropbox.com/s/24qdp1o5q2...15720.mp4?dl=0
    Wow, its like its stuck between a carnival and a horror movie.

  9. #9
    Hedgehog-in-Training Hedgehog-in-TrainingSports Talker
    Join Date
    Sep 2015
    Posts
    37
    Rep Power
    0

    Default

    Tempo is right and all sounds seem to play. Pitch is weirdly off

    Sorry, I've no idea how this could happen. You've got to debug it. Somehow

  10. #10
    Road Rasher superandroidtron's Avatar
    Join Date
    Aug 2011
    Posts
    276
    Rep Power
    14

    Default

    Hrm, I wonder if one of the lines to the Ricoh PCM chip could be messed up, causing corrupted data writes.

  11. #11
    Retro Nutter! Road Rasher Speedle's Avatar
    Join Date
    Mar 2009
    Location
    UK
    Age
    37
    Posts
    383
    Rep Power
    13

    Default

    So some additional fault finding I've done. I've swapped the main board out with a known working one and it works fine with another board. Moving this faulty board to another unit the fault follows the board so it's definitely the main board at fault.

    I did a full cap replacement (as I had spares ready anyway) no difference as suspected.

    So out of ideas really... no idea what components on the board control the pitch. Perhaps replacing the crystal might be worth a shot? I have a spare pretty dead Mega CD for donor parts.

  12. #12
    Hedgehog-in-Training Hedgehog-in-TrainingSports Talker
    Join Date
    Sep 2015
    Posts
    37
    Rep Power
    0

    Default

    No, the crystal would have to run so far out of spec (to produce those pitch shifts) that it wouldn't work at all.
    I suspect it's a bad IC.

  13. #13
    Retro Nutter! Road Rasher Speedle's Avatar
    Join Date
    Mar 2009
    Location
    UK
    Age
    37
    Posts
    383
    Rep Power
    13

    Default

    Fair enough, I changed the BIOS chip out, so I know it's not that particular Chip... Wonder which one it could be... Huff!

  14. #14
    Road Rasher superandroidtron's Avatar
    Join Date
    Aug 2011
    Posts
    276
    Rep Power
    14

    Default

    I'd wager it's the chip marked "Sega 315-5476A". It's in charge of the PCM sample playback.

  15. #15
    Retro Nutter! Road Rasher Speedle's Avatar
    Join Date
    Mar 2009
    Location
    UK
    Age
    37
    Posts
    383
    Rep Power
    13

    Default

    Quote Originally Posted by superandroidtron View Post
    I'd wager it's the chip marked "Sega 315-5476A". It's in charge of the PCM sample playback.
    Thanks dude that's a big help, I will check the traces in that area as there is some cap leakage that could have damaged a trace. Failing that I'll replace the chip with the spares I have

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •