Spy Hunter Sound Interference

[ManiN]

So I had mentioned this in another thread, and thought I'd start a new one. I have been running through a tall list of repairs on a Spy Hunter I purchased months back and am at my last one before cosmetics.

There is a considerable hiss interference sound coming through and is only on the cheap squeak (CS) peter gunn side. When unplugged, the hiss goes away. I can hear sound effects such as machine gun with no hiss.

I have pulled the CS and replaced the caps, and also the MC3340 @ U1 as suggested by another klover in his experiance. CDjump suggested looking at the LM39XX, but I cannot locate that IC. Any help there? I also re-flowed the pins on all connections to the board.

I am wondering if the 12V coming from the linear power supply is dirty for some reason. I recently rebuilt it with Bob's kit. When I turn the 12V pot, I can hear crackling and other effect in the CS sound. The pot is new with the kit. I may try to isolate the power to the CS with an outside source to try and eliminate it.

Thoughts?

Video example of sound (might need to crank the volume):
http://youtu.be/TRSif1x2C2o

 

[That80sGuy]

You've checked and made sure all the grounds are making good contacts? I remember SH has a butt load of them.

 

[cdjump]

did you reflow the solder on the header pins? or just look at them? Reflow them for sure. They always cause problems.
You should also reflow the headers and amps on the sound amp pcb.
I just went and looked at a CSD - they're LM359's, not LM3900s. I was going from memory.

Does the CSD produce sounds? If it does, are they crackly or crunchy sounding? If so, you'll need to replace the dac on it as well.

 

[ManiN]

hey guys, thanks for the replies

Grounds are present. I re-flowed the pins on the CSD, but not the amp board. I'll do that next. The sound plays just fine, there are no real errors, just the hiss interference. It's loud enough that I know there is a problem somewhere. I know some arcade games have noise, but this is more than normal. So the LM359's can cause a hiss you think?

 

[That80sGuy]

How high do you have the volumn? I think there are two seperate volumn pots..one for game sounds and one for the csd. If either one is turned up too much you'll hear that hiss.

 

[ManiN]

Already checked that. The hiss does in fact change with volume, but is quite hissy even at low/no sound position.

 

[That80sGuy]

Yeah.. I remember mine had that hiss. If you unplug the csd does it go away? If not then at least you can narrow it to the audio board in the main stack. Are the interconnect cables on the boardset original .. they can cause issues as well.

 

[ManiN]

Yeah, when I unplug the CSD, the hiss totally goes away and the remaining sound effects come through just fine with great quality. When the CSD is plugged in. Hiss with peter gunn playing just fine.

To recap, all sounds are working fine, even peter gunn, with no error, just that there is a hiss interference when the CSD is plugged in.

 

[ManiN]

Well finally had time to look further. Eliminating wires minus the ground, I noticed the hiss seems to be in the 12v line. I decided to bypass the 12v from the game with a switcher and found the hiss goes away. I believe its either the 12v or the ground from the MCR power supply that is carrying the hiss interference. Anybody have issues from the power supply like this? I rebuilt it with a bob kit. I can't remember if the hiss was there before I rebuilt it, but part of me thinks it didn't hiss this bad. Does the large 50,000MF cap affect noise levels in the 12v source? Looking at the schematic, it doesn't seem too complicated. Any ideas?

 

[barakawins]

spy hunter white noise

I get the white noise on my spy hunter. I think this is normal. I've had 3 spy hunters and all have this white noise sound. Not sure why, but it's there.

 

[ManiN]

White noise is a good way to describe it. It sounds exactly like a TV that has just snow on the screen but not quite that loud. Just enough to know somethings not right and irritating cause it's right in your face (speakers above head). Yeah, you'd would think, but it's pretty loud. My video kinda sucked with expressing the sound, but it's more than just noticeable. If you were in an arcade and walked up to the machine, you'd think Hmmm there's something up with this thing.

If it is something that's just there and I cannot reasonably fix, has anyone ever done like a ground loop isolator, or some kind of filter such as in automotive stereos?

 

[tec9]

My Spy Hunter did it, and I swapped the power supply from another MCR game and it went away.
-Mark

 

[demogo]

I've never noticed this before on mine but it's pretty hard to tell from your video.

Can you do another one that puts it in context with normal game audio?

 

[demogo]

My Spy Hunter did it, and I swapped the power supply from another MCR game and it went away.
-Mark

You swapped the power brick or the linear power board?

 

[ManiN]

Hopefully this is better:

http://youtu.be/ZFH5v9w30eI

The iphone doesn't really capture the depth of the sound it should. It may seem like normal interference, but It's pretty snowy during play. Of course this is nothing like a bad DAC where it's crazy loud and crappy, but it is annoying and not worth overlooking.

 

[barakawins]

Yep

Yep yep... It's normal. All spy hunters do this. I think it is the power supply. If you change to the switcher, it will go away but I didn't want to put in the kit or switcher so I left it alone.

 

[komodo]

I spent about a month troubleshooting a Spy hunter and researched extensively. A hum is attributable usually to the power brick. I did try filters and chokes with no luck. A hiss I am not familiar with so I cannot address that aspect of your issue. I did want to state for the record that every spyhunter I have tried the MCR power supply replacement with made a hum much worse than the original linear power supply and power brick. YMMV

 

[ManiN]

Interesting. Does anyone know if the large 50000MF and 100000MF caps have involvement in power filtering? If they're bad, I'll replace them, but at $15 a pop, would want to know for sure rather than just a shotgun.

 

[barakawins]

hehe

I replaced mine. This is great for the picture! But, the white noise is still there.

 

[ManiN]

How did it improve your picture?