[Tech] Buzzing sound

[guddler]

[ukvac] [Tech] Buzzing sound
I recently got the sound working on my "The Pit" board, but now it
buzzes quite loudly all the time. I know the amp I replaced is a good
one as it worked perfectly when I wired it up as a separate amp to the
board. I then stuck the amp IC in the board and I get loads of buzzing.

I spent some time this evening replacing (as a long shot) all the caps
and resisters that form the rest of the audio circuit, and a couple that
smooth the +12v (one of these was 1000uF), but still no luck.

I think it may be video related as the buzz changes when the screen
changes and the more black the screen has the less of a buzz it makes,
BUT I checked out the adapter that I made and the wiring all looks good.
One thing that I was suspicious of was the speaker - is connected to
ground which is the same ground as the video gnd, but removing the video
gnd (and sync for good measure) makes no difference whatsoever.

So, unless I shagged the amp fitting it - which I shouldn't have done it
was all pretty straight forward, I'm stuck for where else I should look.

Anyone got any ideas please as this buzz is REALLY annoying me??

Cheers,
Guddler.

-------------------------------------
Martin White

http://www.guddler.com
Arcade search site with PCB info too...

 

[Macro]

Re: [ukvac] [Tech] Buzzing sound
LA4422 amp chip ?

is it anything like a make trax PCB

if so, check out the maketrax repairs on my site www.arcades.org.uk as I had
a similar problem with crazy painter / make trax hardware and found a
solution that you may be able to adapt. (and yes, the brighter the screen,
the nosier it was!)

 

[guddler]

RE: [ukvac] [Tech] Buzzing sound
No MB3730 amp, but I shall certainly take a look anyway, cheers...

-------------------------------------
Martin White

http://www.guddler.com
Arcade search site with PCB info too...

>

 

[dz1n3]

Re: [ukvac] [Tech] Buzzing sound
Is it a buzz or a humm, one will be a dc offest problem and the other will
be cross talk of some description, and allmost certainly a power problem,
scope the dc line in on the sound chip nice straight line hopefully and not
bouncing up and down. and also check the gnd too, sitting at 0v with no
interference. check these and you should know what your looking at then.

Hmm, this aint like me!! <SORRY>

D!

 

[guddler]

RE: [ukvac] [Tech] Buzzing sound
A buzz I think! Not much difference between a buzz and a hum tho is
there?!

Anyway, good info - bit busy at the mo but I will scope those lines when
I get a chance. Suggestion was (that I was going to try) to put a cap
(say) 220pF between the last point BEFORE the input pin on the amp - but
not at the pin - and ground.

Cheers,
Martin.

-------------------------------------
Martin White

http://www.guddler.com
Arcade search site with PCB info too...

>