Has anyone installed a SMSFM board in a PAL EU SMS2 console? Buzzing problems....

[keropi]

Hello!

has anyone installed a SMSFM board in a pal sms2 ? I get some very nasty sound parasite , I made a video about a month ago:
http://www.youtube.com/watch?v=91-SQP8Sjc8

In that past month I have sent my SMSFM board to Tim (the seller of the boards http://members.iinet.net.au/~stinkyf...sfm/smsfm.html ) to check it and he sent it back because it is OK. Installed it back from scratch and still got the parasite.
So I thought it was the console I am using and I just got a second sms2 console and installed it once again from scratch. I am also using mmmonkey's SMS2 RGB AV RGB port mod, with a small change: instead of composite to the rgb port I feed it the c-sync signal to get rid of the annoying jailbars. I still have composite output modded , just on a dedicated RCA. But I am still getting the same buzzing sound!

Keep in mind that when the SMSFM board is NOT connected to the sound output (ie I get the normal SMS sound output) there is no buzzing at all. Everything works fine in both consoles and I am using a standard MegaDrive1 RGB scart cable that works fine on a md1 console. mmmonkey's mod is specific to using md1 cables btw.

I don't understand why I can't get it working properly. The FM chip gets detected and used. Tim verified it works fine. I tried on 2 consoles with the same results... both work fine with rgb/composite without the smsfm. Is there some sort of weird conflict for pal sms2 consoles?

I am attaching some pictures of my 2nd install, maybe someone can suggest an improvement or have an idea of what to try...

SMSFM installation pics:














RGB pics (nothing important really , using mmmonkey's instructions) :






Any info or thoughts will be appreciated, thanks in advance! :)

[Hedgeyourbets]

I experienced the same buzzing when just doing the RGB mod for someone
In the end I found that i couldn't eliminate the problem entirely but i could reduce it to a level where it wasn't noticeable. I had to wire the entire scart cable a little differently

[keropi]

I know what you mean but this does not apply on my case with the sms2 consoles because both of them have almost no noise when they output rgb with the sms2 onboard audio. That led me to believe that the smsfm has some kind of problem but it was sent back to Tim, he tested it extensively and found no problems. But he did test on SMS1 console(s) AFAIK.
I believe there is some sort of problem with the sms2 consoles , but I have no idea what this is :(

[omp]

I have done this twice (well technically 3 times but I swapped out a rev 1 board for a rev1.1). I don't recall any buzzing though. One of them has been modded for rgb out, allthough it goes to a component converter so no jail bars (OT). I will have a look again soon. I did have an audio noise on the rgb one but that was due to a shit quality splitter (the mega drive/32x/mega cd combo was connected to this as well.)

[keropi]

I have an update... I showed the machine to a friend and suggested we solder a ceramic cap between the red+white wires of the SMSFM (input from PSG and mixed output of psg+fm).
So we added a 680pf cap and the buzzing sound almost disappeared... you can still hear at a lower volume but only when I have the volume of the tv to 80% or more, I think that's normal as it's way too loud.



what do you think of this? is this a good idea to have this cap there?