audio buzz question.

[bozo55]

Pics (sorry if these pics suck, I had to resize them a lot so that they would meet the forum guidelines):

[bozo55]

More pics:

The first one shows what I think is a corroded via? (Right below the C616 text)

The second shows what I believe is one of the opamps for the sound.  One of the legs looks very dull.

[Keith Courage]

There could be broken traces around the caps you have shown or even shorts under the op amp due to old cap goop. Bridge some solder leads through some of those via holes and see if it helps. If not then remove the omp amp, clean up really well, then reinstall.

[bozo55]

Thanks Keith.  I'm gonna give it a shot ASAP and see how it goes... I really appreciate all your help.

[bozo55]

So I cleaned the headphone jack and AV out with contact cleaner and checked points for continuity.  All the op amp pins and traces around it have continuity.  The via that looked bad had continuity.  I didn't check continuity on the underside of the vias yet though. 

The thing is, I can't really reproduce that problem I was having anymore    sometimes I think i hear some static but it's too faint to really say for sure, even at max TV volume.

I did notice why the GameDoctorHK cables suck though.  If you look at the attached picture, you can see that on the left cable (official Genesis 1 AV cable) the Ground ring bump is much bigger, and presses better on the ground pin of the AV out jack of the Turbo.  The crappy cable has a very puny bump.

[Keith Courage]

static and crackling can also be caused by old cap goop underneathe the op amp closest to the m5205 chip under the board. Maybe check there.

this problem usually goes away after the system warms up

[bozo55]

static and crackling can also be caused by old cap goop underneathe the op amp closest to the m5205 chip under the board. Maybe check there.

this problem usually goes away after the system warms up

I'm afraid to pry off any op amps, so I will try just spraying some of my MG Electronics contact cleaner spray to see if that helps first.  The video showing the problem was with the system having been on for well over an hour.

[bozo55]

So I was playing Keith Courage for about 15 minutes, and then the sound became distorted and started to slowly fade until there was no sound... hmmm.  So this problem gets much worse with heat it seems.  I'm gonna pull this board apart and examine it carefully.

EDIT: letting the system rest for a few minutes gets the sound back.  This is a pain in the ass to fix since it is so intermittent.

EDIT 2: I drenched the areas around the op amps under the board with alcohol and contact cleaner spray and wiped with a Q-tip as best as I could.  I've had the system running for nearly 2 hours straight now on Keith Courage and can't get the sound to glitch out.  I'll have to run it for more time to see how things go.

[Keith Courage]

So the sound went away altogether? Sounds like a bad trace near the M5205 op amp or a bad trace near the AV jack op amp.

[bozo55]

So the sound went away altogether? Sounds like a bad trace near the M5205 op amp or a bad trace near the AV jack op amp.

Yeah, well, I could very (very) faintly hear the sword strike sound effect, except it didn't sound correct.  It sounded mostly like faint static, and the BGM was completely gone.  It faded out slowly over the course of about 1 minute.  First it started to distort, then the volume dropped gradually until the sound was gone. 

I turned it off and back on right away and the sound was still completely gone.  After leaving the system off for 5 minutes, the sound came right back to normal.   

There is no sign of trace wear whatsoever on the bottom.  I'm hoping that cleaning it fixed it.  I am going to keep testing it and report back.

Thanks again Keith.

[Keith Courage]

If the sound goes away again, leave the system on and double check the 22UF cap to the left of the M5205 chip. Make sure it's getting 3.7 or 3.8V

Also double check that the op amp near the AV jack is getting the same for the positive lead.

both of those areas are notorious for old cap damage.

[bozo55]

If the sound goes away again, leave the system on and double check the 22UF cap to the left of the M5205 chip. Make sure it's getting 3.7 or 3.8V

Also double check that the op amp near the AV jack is getting the same for the positive lead.
both of those areas are notorious for old cap damage.

So I put the red probe on the + end of the cap and the black probe to the ground plane of the board?  This board has no exposed ground plane... Where should I probe for ground?

Which pin on the 4558/2819 op amp is voltage? I think it's pin 2???

Thanks Keith! 

[Keith Courage]

my mistake, you don't want to check the main power lead for the op-amp. You want to check the top right lead which should read close to 3.8 volts.

grounding plate for the power switch works best.

[bozo55]

my mistake, you don't want to check the main power lead for the op-amp. You want to check the top right lead which should read close to 3.8 volts.

grounding plate for the power switch works best.

Oh so I should test Pin 5 of the op amp.  Sweet.  Thanks again Keith.

[Keith Courage]

there should actually be two leads on the op amp that have this voltage. also same on the 22uf cap next to the AV jack op amp.