Kurzweil PC3X electronics issue

[ivorycj]

Hi all,

First time poster here. I checked around, and didn't see any stickies about 'NEVER POST HERE' or 'ONLY POST HERE', so I believe I'm in the right place. I have a Kurzweil PC3X that has been repaired by 2 technicians, only to have the same issue. Both of these technicians are well qualified - I used one for many years as the exclusive tech in the Colorado / Wyoming region when I was the Kurzweil rep (2003 - 2010). I'm hoping someone can shed some light on the problem. See this video:

https://www.dropbox.com/s/t49qm5o4f5...noise.MOV?dl=0

This noise is random - it appeared today after said Kurzweil was on for a number of hours with light playing. It most often appears after a few hours - the best time is about hour 3 or 4 of rehearsal when everyone is tired and my master volume is all but maxxed into our Mackie DL32R that we all use in-ear monitors with. Wakes us RIGHT up.

It sounds like it's coming from the output section - maybe the DAC's? All I know is that I'd really like to use this board live and leave my PC3K8 in the studio - which is now in the road case as my main axe.

Feel free to email / PM me with any ideas. The right one may very well get some industry swag from me (I still rep a number of cool guy products in the industry)

Thanks!

CJ

[The Dude]

Welcome to the place!
You may want to remove your email from the post,......unless you enjoy spam. I would not post my personal email publicly anywhere on the web. Forum members can PM you directly here if they choose, so publishing your email is not necessary anyway.

Edit: As to the problem, all we know is that it's "pre volume control" which does narrow it down. Without a schematic, it becomes difficult from there. Do you have a schematic you could post?

[ivorycj]

Thanks, The Dude. Ever shop at Sioux Falls Music? I used to be their Kurzweil rep a lifetime ago...

[The Dude]

.... Ever shop at Sioux Falls Music?...

Yes I have and I often do repair work for them. I also ran a pro audio store in town years ago called Gourley Pro Audio. Did you by chance rep any of their lines?

[Enzo]

OK, several thoughts.

Two repairs by different guys? And do you still have the repair tickets, or remember what was done? I mean specifically, "I think they soldered something" doesn't count.

Turn it up enough to hear, then swat it with your palm. Does that have ANY effect? Slap the bottom, hold up one end to access the bottom. Give it a fairly hard rap, it won't hurt it anymore than animated boogie playing. Also rap the ends of the unit. If it momentarily stops it or cause any change, even briefly, that is evidence of a bad connection inside somewhere.

Even so, inside I would partially pull then reseat every internal connector, and try wiggling each while it is doing it. I would also firmly press down on the middle of each board to see if that bit of flex changes anything.

It sounds to me like some analog stage is motorboating, but it could also be a stuck bit in the digital domain. The former could be a missing ground connection , the latter a bad solder joint on an LSI somewhere.

But we REALLY need a schematic or service manual, because we cannot point to anything in the circuit without a circuit map. I no longer have a PC3X manual here. If I can borrow it back from its current owner I will, but don't hold your breath.