Clavinet C wiring/sound problem

Started by DickyFingers, August 03, 2022, 11:51:28 PM

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I am currently restoring a Clavinet C and have run into an issue.
Please forgive me as I am not extremely well versed in the field of electronics. However, I am always trying and willing to learn and would very much appreciate if anyone has any help they can provide!

I purchased and installed replacement DC jack plate from Vintage Vibe.

I was not getting any sound whatsoever from the unit using battery or PSU. Only a pop when turning it on.
I tried cleaning the switches, disconnected both pickups and checked their continuity (176+205 ohm).

After reconnecting the pickups, I noticed by accident that if I reverse the battery leads I get good tone from both pickups in all switch orientations, however it comes with a loud, constant scratching noise in the background. Here is a link to audio example

If I put the leads back, no sound again.

Does anyone have any idea what would cause the unit to only work on battery with reverse battery leads? And why the accompanied noise would be so loud?

Is it likely that the preamp components have been damaged due to the reverse battery hookup? 
Link to more images:
Here is an image of preamp and my PSU, that is the correct PSU right? 9V DC 300ma center negative? 
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Center negative is correct. Was this problem happening before you installed the VV plate?


I just spoke to Vintage Vibe and they were very helpful. My Clavinet now works with both the battery and power supply!

It turns out the instructions that came with the DC Jack plate were not correct for this specific model (clavinet C).

From Vintage Vibe:
"I think the issue here is that the Clavinet C preamp design uses PNP transistors and thus it is a positive ground circuit. You need to switch the polarity of the DC wiring to match this."
They provided new wiring instructions.

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Quote from: theseacowexists on August 05, 2022, 09:34:55 AMCenter negative is correct. Was this problem happening before you installed the VV plate?
Yes it was. Thanks for clarifying on the center negative