donnysparks

yamaha pm1000 troubleshooting help needed...
« on: March 12, 2007, 08:44:39 PM »
Hi all.  i'm having some trouble with a module that i've racked.  this is my 4th time through racking a pair of these, so i guess i've been lucky to not have had trouble sooner:

the module passes audio only in the first 5 positions of the input gain switch.  from the 6th position on the audio disappears.  you can still hear a faint (60hz?) hum in the background after the audio is gone, and this gets louder and softer with adjustment of the output pot.  the hum is present in all settings.  

Initially it would only pass audio in the 3rd through 5th positions.  i replaced a transistor that looked suspicious to me and arrived at where i am now.  i would go ahead and replace them all but i don't have enough to do it right now.  i'm hoping someone might be able to tell by looking at the way the input switch is set up on the schematic:

 http://www2.yamaha.co.jp/manual/pdf/pa/english/mixers/PM1000E_2.pdf

also, strangely, when i touch the tops of C10 and C11 i get a buzz.  doesn't happen anywhere else...


any ideas?  thanks in advance for any help.  i'm obviously going to need some beer.  be right back!
--donnysparks


raysolinski

yamaha pm1000 troubleshooting help needed...
« Reply #1 on: March 12, 2007, 09:51:54 PM »
There is a problem in the first amp section. The first six positions of the switch bypass the first amp section..in the last positions the first amp is brought in to get the full gain....replace the caps and transistors in the first section (before the eq)..you might want to check the input tranny as well. Make sure the there are no loose connections in the wiring to the switch itself.
Check the voltages throughout that section to see if there is a short...just a few thoughts. Been a while since I poked around in my pm's...

Cheers,
Ray
"orange whip?..orange whip?...3 orange whips please"

donnysparks

yamaha pm1000 troubleshooting help needed...
« Reply #2 on: March 12, 2007, 11:59:53 PM »
Thanks very much, Ray!  I was hoping you would see this as i remember you had a similar problem a while ago.  Your advice makes sense.  i'll go try replacing the parts from the first preamp section.
--donnysparks

donnysparks

frustrated now
« Reply #3 on: March 13, 2007, 11:21:18 PM »
alright.  i guess i need more help.  i've replaced every component in the first gain stage (Ray, the first gain stage is the group of caps/transistors that is closest to the input tranny, right?).  

~still no signal from position 6 onward.  

~i've confirmed continuity in all the resistors on the board, replaced all caps and         transistors in that first section, and gone back over every solder joint.  

~i've ruled out the input tx b/c i get the same thing with the DI, which is inserted after the tx.  

~i am positive i have it wired properly.

~i tried making a test probe out of a small pc speaker but i couldn't get that to work.  how the hell does that work, anyway? from the speaker i connected neg terminal to 0v and pos term to a test lead.  touching the test lead to "tip" of a dimed line level signal from a keyboard yielded NO sound.  i know i need something stronger than line level ideally, but shouldn't i hear something?

If anyone can check the schematic for the most probable failed component i would be so thankful.
--donnysparks

Jed

yamaha pm1000 troubleshooting help needed...
« Reply #4 on: March 14, 2007, 11:01:56 AM »
This is just a shot in the dark, but you might check to see if there are any cracks in the pcb. On one module I racked up there were several hairline cracks that I didn't notice until pretty far along in the racking process. Once I found them it was a fairly simple matter to bridge the bad connections.

I did a test probe in a not too dissimilar fashion, but I just used a guitar amp. I took a 1/4" cable and cut one end off. I put an alligator clip on the ground wire and clipped that to the board ground. I then used the positive wire as my test lead. For a signal source I just used a song and had that run on a continuous loop out of my daw.

The only problem I had with this method was having The Velvet Underground's "The Ocean" stuck in my head for 2 days after finishing my tests!
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donnysparks

yamaha pm1000 troubleshooting help needed...
« Reply #5 on: March 14, 2007, 11:51:52 AM »
Quote from: "Jed"
This is just a shot in the dark, but you might check to see if there are any cracks in the pcb. On one module I racked up there were several hairline cracks that I didn't notice until pretty far along in the racking process. Once I found them it was a fairly simple matter to bridge the bad connections.


thanks! i'll check for that.

Quote
I did a test probe in a not too dissimilar fashion, but I just used a guitar amp. I took a 1/4" cable and cut one end off. I put an alligator clip on the ground wire and clipped that to the board ground. I then used the positive wire as my test lead. For a signal source I just used a song and had that run on a continuous loop out of my daw.


ahh, i see.  good idea.  i'll do that one, too.

Quote
The only problem I had with this method was having The Velvet Underground's "The Ocean" stuck in my head for 2 days after finishing my tests!


not the worst stuff at all to have stuck in your head.  definitely better than Rick Astly's "never gonna give you up" which is the demo song on a casio that i used for my test source.

thanks all for the help so far.  please keep the ideas coming.
--donnysparks


 

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