audio buzz question.

[bozo55]

Okay, here's a video of this problem:


Sorry for the lousy one-handed gameplay

I noticed something strange... pressing on pin 3 of the op amp only brings the sound back when the meter is on???  Why is that.  If I just press on pin 3 with the meter off I get nothing.

[thesteve]

ok my turn
check the 4 via around C323 (directly right of the amp by the AV jack)
chances the one on the right of the 3 together is bad

[bozo55]

ok my turn
check the 4 via around C323 (directly right of the amp by the AV jack)
chances the one on the right of the 3 together is bad

Thanks Steve.  Gonna clean those vias and flow some solder in them to make sure they're making good contact.  I'm gonna give it a go tomorrow.

[bozo55]

I think I found a glaring issue.

When I put the board up to the light, the traces look like the + end of C323 is supposed to be connected to pin 3 of the op amp.  I have no continuity there. 

It's hard to tell if the traces are from the top or bottom layer so I'm unsure.  Can anyone confirm before I jumper this trace and blow up my Duo lol.

Thanks everyone.

P.S. I couldn't find any issues with the vias around C323.

[thesteve]

that is correct

[bozo55]

Thanks Steve.  I'm gonna jumper it and see what happens 

[bozo55]

So I jumpered pin 3 to C323. 

The static I get out the right speaker is still there.

However,  the sound has yet to distort and cut out.  I have to do more testing, but I think I've made some progress here.  Thanks to Keith Courage and thesteve for all your help, you guys are like the PC Engine Whisperers 

[thesteve]

meter touching pin3 shouldnt have any effect

[bozo55]

meter touching pin3 shouldnt have any effect

It only seemed to when I had the black lead on the power switch ground plate and the meter turned on.  With the meter off it did nothing.  I don't get why it helped.  Maybe when I was pressing in the video I was actually reconnecting the bad trace  .  But I pressed firmly with the meter off and it did nothing, turned the meter on right after and voila. 

Update: I've been playing Air Zonk for a while now and I'm on the 5th stage with the sound still intact.  Before I jumpered the wire the sound cut off on me by stage 2.

[thesteve]

that pin floating would have the meter complete the circuit

[bozo55]

that pin floating would have the meter complete the circuit

That must mean that trace is unreliable since it was having that issue before I removed the op amp.

[bozo55]

I started fudging around because, why the hell not I guess.  I bypassed the via beside C616 by jumpering the cap directly to pin 4 of the op amp directly below (IC521).

It may be my imagination but I haven't noticed static in the right channel during my last play-through of Zonk.  I still am not satisfied with the audio volume.  I don't get why my US Turbo is so much louder.  My Turbo is unable to work with the Everdrive however, and it is getting recapped soon.  Maybe the audio will be different once it's recapped, i.e. quieter.

One thing I notice with my Duo when I compare it to my JVC X'eye is how loud the X'eye is, yet how little hiss it produces.  The Duo puts out way more hiss, and is way quieter.  I should have the genuine AV cables soon enough so hopefully those will help.

[bozo55]

I got my genuine NEC AV cables in today from ebay.  They're pretty beefy, especially compared to the lame Gamedoctor cables.

The hissing is definitely way less . Volume is still the same however.  Much quieter than my Turbo.

The static reappeared in the right channel

I'm going to remove the 2 op amps on the underside of the board and see if cleaning under those helps.