Author Topic: Neve 33609 J problem please help  (Read 898 times)

Rob Flinn

  • Member
  • Posts: 3076
  • Sussex, UK
Neve 33609 J problem please help
« on: March 12, 2011, 11:00:53 AM »
I have a unit I'm trying to repair that has some strange issues

1.  The right channel has a permanent slight hum, which only appears when the compress section is switched in
2. Occasionally a loud hum with a modulation appears which gets louder & then sometimes just reduces back to nothing & leaves the slight residual hum.   Other times linking for stereo & then unlinking clears the hum.  When the unit is linked for stereo the loud hum appears in the left channel, but only when it is also in the right channel.  When this loud hum is present the make up gain switch becomes very clicky.  This would make me think perhaps there is a flaky cap, but since when I swap the channel audio boards the hum stays on the same side it appears to eliminate problem being a cap.

So far

I have swapped the audio boards & the fault is still with the right channel. This leads me to believe that the problem lies somewhere either in the wiring harnesses or the compress controls, but I haven't found a fault there.

If anyone has any ideas I'd love to hear them because I've spent a lot of time on this already.
regards Rob

Capital letters.  The difference between helping your uncle Jack off his horse, & helping your uncle jack off his horse ........


radardoug

  • Member
  • Posts: 176
  • North New Zealand
    • Doug Jane Recording
Re: Neve 33609 J problem please help
« Reply #1 on: March 12, 2011, 03:11:11 PM »
Sounds like a dry joint in the wiring. The hum points to possible power supply or ground issue. Look at the filter caps to see if there's a dry on them. I'm afraid it's just going to take detective work on your part.
Try pulling at the harness in various places to try and get the fault to happen. And judicious banging around the components. Once you can create the fault, its usually easier to home in on it.

Rob Flinn

  • Member
  • Posts: 3076
  • Sussex, UK
Re: Neve 33609 J problem please help
« Reply #2 on: March 13, 2011, 08:41:58 AM »
Doug thanks for the response.

I think it's unlikely to be a PSU fault since the other side is working OK with no residual hum or the intermittent problem. I also replaced the main smoothing cap, but there is some residual ripple before the LM317, but none afterwards.   Since I've swapped the BA640's & the whole audio boards & the problem stays on the same side the only thing left is the harnesses which all have been pulled & buzzed out with a meter, & the front panel controls/switches. 

Since my last post I managed to get a scope on the output  of the channel whilst the intermittent problem was happening.  The wave form showed showed regular lumps going positive only.    Not like a sine wave with no negative half since there was too much space between the pulses.   The sound is kind of like a raspy hum. 

I've also already done the prodding routine & can't get the problem to occur when I want it to,

Any other ideas would be welcome




regards Rob

Capital letters.  The difference between helping your uncle Jack off his horse, & helping your uncle jack off his horse ........


 

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