crackles and pops. re-cap time?--388 related

  • Thread starter Thread starter williambslack
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Ok, I pulled all the cards and listened--nothing bad happening. I kept adding cards, but I wasn't hearing any problems until the last card was added, which was the DBX card for Ch 5-8. Once that card was in, the same ol problem returned, but only on channel 6 as usual.

Well this seemed encouraging at first. I left that card in, then removed ch1-4 DBX card and checked--same problem. Then I removed ch 6/8 card--same problem. At that point I thought surely it was a DBX card problem, but then I removed the DBX 5-8 again, and the problem continued!

A this point I put all cards back in--problem continued.

I tried putting pressure on the cards to make the noise occur, but none of my actions seemed to correlate to the fizz/pops.

Then I switched between RMX and LINE, and did seem to notice come correlation between putting downward pressure on the switch and the pops. Does this mean anything? Could it be the switch?

Thanks
 
Well, sure it could!

Do you have any DeoxIT D5 or a way to get some?

That would be my suggestion is to get some of that and inject it into the switch body from the underside and exercise the switch. If that doesn't do it then maybe there is a bad trace or land around that switch.

There are no components between that switch and connector on the card that brings the signals from the line and rmx sources. It could be that oxidation or soilage is causing poor contact that manifests depending on the loading of the bad contact. The other thing to do while you've got it up on its side with the bottom panel off is to exercise the connections to the mixer card.
 
I believe I do have some moving contact cleaner somewhere around here. So, are you saying it's easier to get to that switch body from the bottom than it is to take off all the knobs and such to remove the top panel?

Exercise the connections to the mixer card:

1) I assume this just means to remove the card and re-insert it, yes?

2) When you say the mixer card, do you mean the card that makes up the channel 6 strip (trim, EQ, Aux send etc.)?

THANKS Sweetbeats!
 
Dont remove the top panel!
Its a bitch to line everything back up when trying to put it back on.As Sweetbeats said...Go in from underneath.

And yes.The Channel card has the eq,eff,trim etc....Just be very caerfull when removing the board that runs along the bottom of them all.
Do this very carefully!
 
Yeah, I actually have removed the top panel before, so I'm glad to hear the bottom is easier. I accidentally reversed the two pgm faders (odd to even, even to odd) when I reassembled the top, but I would rather just deal with the minor inconvenience than take the top off again.

I'll report back once I've cleaned the switch.

THANKS.
 
I took off the bottom and sprayed deoxit into the the switch body--i actuated the switch a handful of times. I exercised the mixer card connections as well.

I turned the unit back on and Channel 6 still had the problem. Then I checked the other channels, and the problem began to occur on almost all channels! (Let me mention again, if it helps, that I am only hearing the problem when in RMX mode, not line mode or Mic mode as far as I can tell).

So, I actuated all the switches a bunch, but this doesn't seem to help.

I seemed to have made the issue worse, so I hope this at least helps to narrow down the issue.

I'm totally stumped--what should I try next?
 
it is occurring in rmx mode with the amp cards removed?
 
It did not occur at all with the amp cards removed, but the DBX cards were removed as well. Perhaps I should have tried it with DBX cards in and all amp cards out?
 
Can you hear the noise at the TAPE OUT jacks as well?
 
Sweetbeats,

NO, there's no noise at the tape outs. BUT, today I have yet to hear noise at the sends either! This actually seems more frustrating then good. I guess, in terms of chasing this intermittent problem, the tape outs are clean for now, but it could just be that the problem isn't occurring at the moment.


THANKS.
 
Okay, the next step really is to just wait until the noise is occurring again at the send jacks and at that time see if it is also present in the tape out jacks. This would be with all cards loaded. Also make sure, other than the cables you have connected to monitor for noise, there are no other connections made to the 388. And do this: re-seat the rest of the cards in the cardbay (the 4 cards on the right half of the cardbay).
 
OK, for now I'll wait until the problem returns.

I reseated the cards to the right, and noticed a heat-damaged area on the Reel Servo PCB. ANyway, this could be totally unrelated, but I thought I'd post pics. Something I should replace? What is that part?

Thanks.
 

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Power transistor. They get hot. Its okay. Even if it was toast it wouldn't cause noise in the audio path.
 
Ok, Sweetbeats, the problem is back today. (I was listening to some tape and I heard it through the monitor outs, though it wasn't printed to the tape).

I disconnected everything and listened to a few of the channel sends, and sure enough the crackling was there. I did not at any point hear the problem on the tape outs, however. I went back and forth between the two for a while to make sure it was still occurring at the send. So, perhaps we can rule out the tape outs.

What does this tell us?

THANKS.

EDIT: i hooked the monitors back up to the stereo outs and the noise seems to be more of a problem than ever. The crackling and pops go away with the stereo master fader turned down. This probably doesn't help narrow it down since I imagine anything causing a problem would lead to the mains, but I thought I'd mention it. This problem seems to be growing as we look for it.
 
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The other day when I took out all the cards I heard no problems, but I was thinking this could have been just the intermittent thing not occurring. So, I just did the following:

removed both DBX cards--still had noise

removed each record/play card, powering up each time to check. The noise persisted, even once all cards were out.


I don't quite understand (not seeing on the pictogram) the signal path to this send we're testing. In line mode, the problem isn't heard, so I assume this means the problem is before the switch. In RMX mode, AND with all cards out, the problem is occurring at the send, and at the stereo outs, but not at the tape outs. Does this narrow things down?
 
I'll take that info and compare to the logic diagram and schematics and get back to you.

So, just so I'm clear, no dbx or amp cards installed, input sourced to "rmx", noise is heard in all 8 channels at the "send" jack and the "stereo out" jacks but not the "tape out" jacks 1 thru 8, correct?
 
Maybe I'm missing it, but I don't see the signal path to the channel send on the pictogram signal chart. Can anyone explain the path, particularly in RMX mode?
 
When you can hear the noise in the stereo out jacks, are you also able to hear it in the monitor out jacks and in the headphones?
 
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