Time Pilot - Erratic Sound - Need Help

PhoenixStar

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Picked up a Time Pilot, had no sound. I did a few basic things as listed below, and now I have sound (kind of). Certain sound effects fade in & out, certain sounds maintain constant normal volume, and some sounds you can barely hear. This is what i've done so far.

1) Had no ohms on the original 5" 8K speaker, replaced the speaker with new 4" 8K speaker (couldnt find a 5" anywhere).

2) Cleaned & wire brushed every chip on every board.

3) Tested Volume pot on board. Resistance seems normal and ranges from 10K to 0K when it is adjusted.

I did notice that when I turn the volume pot, you can hear the wiper on the inside of the pot come through the speakers as very slight distortion, and i've never heard that before. This would lead me to believe on a bad pot that all volumes for all SFX would be at equal volumes, and not have different SFX fluctuate at separate volumes. Is that correct? What else should I check?

Thanks!
 
It seems to me I've heard that TP boards are prone to having bad caps in the audio circuit, I've got one at home with no sound that I've been meaning to check that on, but I don't know anything more than that.
 
Do you know which caps belong to the audio circuit? I may be willing to attempt my first cap job if I knew for sure which ones they were.
 
Easy way: If it's an electolytic cap ("can" style), and fairly near the volume pot or audio amp (usually the heat sinked component), it's in the audio circuit.

Less easy way: consult the schematics, http://arcarc.xmission.com/PDF_Arcade_Manuals_and_Schematics/Time_Pilot_Schematics.pdf

Ok, hypothetically speaking...

1) Could it be the volume pot itself if certain sounds go in and out & change volume levels individually? Or would the pot control every sound at even levels? It seems to have proper resistance levels when tested with a multimeter.

2) Could the amp itself cause a fluctuation with individual sounds, or not? Are you saying it may be the caps that power the amp may be bad?

3) I solder daily, but never a PCB. Is replacing a cap as simple as heat up the solder, pull it out, and pop a new one in? (of course matching correct polarity & mf). I have a Weller Solder Gun, but it's not heat controlled. Is there a major risk damaging the cap if I solder it very quickly to expose less heat to the cap?
 
Ok, hypothetically speaking...

1) Could it be the volume pot itself if certain sounds go in and out & change volume levels individually? Or would the pot control every sound at even levels? It seems to have proper resistance levels when tested with a multimeter.

2) Could the amp itself cause a fluctuation with individual sounds, or not? Are you saying it may be the caps that power the amp may be bad?

3) I solder daily, but never a PCB. Is replacing a cap as simple as heat up the solder, pull it out, and pop a new one in? (of course matching correct polarity & mf). I have a Weller Solder Gun, but it's not heat controlled. Is there a major risk damaging the cap if I solder it very quickly to expose less heat to the cap?

1) If you are SURE that it's not all of the sounds being effected, and not just the entire audio changing whilst different sounds are being generated... then no, I woudln't think the volume pot would be a likely issue. The volume pot effects the ENTIRE mixed audio signal.

2) Not really, per se. But I suppose it could be effecting different frequencies differently, which may end up seeming like different sounds are individually effected... The cap thing is just a fairly common issue with audio problems, and it's typically fairly cheap and easy to do, so if I'm having analog audio issues, the caps often get changed pretty early on.

3) The cap will be fine. But don't linger too long (more than 4 or 5 seconds or so) on a joint, so as to avoid damaging the traces on the board.

Personally, I doubt the issue is the caps... but I hope I'm wrong and it turns out to be.
If it's truly as you describe, individual sound sources, then I'd expect to find the problem before they are mixed together. The first possible cuplrits that jump out at me are the 4066 bilateral switches used to turn on/off individual voices. Still, I'd probably replace the audio caps first.
 
Personally, I doubt the issue is the caps... but I hope I'm wrong and it turns out to be.
If it's truly as you describe, individual sound sources, then I'd expect to find the problem before they are mixed together. The first possible cuplrits that jump out at me are the 4066 bilateral switches used to turn on/off individual voices. Still, I'd probably replace the audio caps first.

I'll change the caps first since it's the easiest thing to do. If that dosent work, i'll have to dive deeper into discussion with those switches.
Thanks.
 
ok that's the second time I heard about this. Can you point me to a thread or something I can read to gain some knowledge about identifying, and replacing them?

1) The easy way: start looking within a few inches of the amp for any IC with the numbers "4066" printed on it. There will likely also be letters/numbers before and/or after the 4066; ignore them.. just find things with "4066." If it's not 14-pins, ignore it.

2) The less easy way: consult the schematics (linked earlier).
 
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