Kenwood L-07C preamp. Gain Attenuators problem:(

[Scottidog]

Hi,
My beloved Kenwood l-07c started to have issues_scratching and weak sound on left channel. I think the problem lies at the gain attenuator/balance control. I opened it up and intended to clean the attenuator with contact cleaner but could not as there are no openings on the part for the contact cleaner to get in. I spayed some cleaner there anyway. All 2 channels worked properly briefly and then gone bad again. There is so LITTLE info on the Kenwood L series amps. I am hoping someone might have knowledge on the problem with the Kenwood. It is really a wonderful preamp. It has served me so well with my pair of Kenwood L-09M. I will be so upset if I can not get it fixed.
Thank you so very much everyone in advance for lending a helping hand.
Regards,
Mark

 

[rayma]

You should be able to replace the old control with a modern equivalent control.
The board layout may not fit most controls, but a bracket could help this.
Use the same resistance value for the replacement control.

The technical manual is here:
Kenwood L-07C - Manual - High End Stereo Control Amplifier - HiFi Engine

 

[Galu]

If you can't find an access pont for the contact cleaner, it would appear to be a sealed dual concentric pot.

Unless a sealed pot can be dismantled (difficult) for cleaning, the only option is replacement.

If a dual concentric replacement is hard to find, and you don't often need the balance function, you could use a standard stereo pot and join the two separate halves of the volume knobs together with glue or a connecting pin.

Kenwood L-07C on thevintageknob.org

 

[Scottidog]

Thank you Rayma and Galu for the quick responses. Your ideas assured me that there will be options if the pots is indeed dead and cant be repaired. I will download the manuals to study it more. With the covers off, everything looks very clean inside and nothing looks had been touched. I am also wondering if it is sth else causing the problem. I am going to switch things around Later today and see if problem persist.
Thanks again,

 

[rayma]

Maybe it's worthwhile removing the control and trying to clean it. There may be small openings that are not visible now. Use only a brief shot of cleaner at a time, though. More is not better. Exercise the control, another shot,
and more exercise. Then try it out. It is possible that the control is worn out, but if it worked for a while after cleaning, maybe not. Also clean the subsonic switch.

There is a series output muting relay that could be bad as well. You could try bridging the output relay contacts
to see if that cures the problem. If so, then I would reconnect it as a shunt to ground rather than in series.
It is after an output coupling capacitor, so that would be ok.

 

[tvi]

You can get an idea of what s need to clean these type of sealed control here:
??????????

hope it helps

 

[Scottidog]

I posted a message yesterday that did not show up here somehow.
I moved the combination of the balance/gain att in a position where i am able to hear all channels sound out “good” now. There is still scratch noise from that same channel at”that bad setting” of the gain att.
Tvi, that is it what can be done. Reading from service manual, there is a specific illustration on what to do with the “attenuator” in that the wafer can be replaced, not the entire rotary switch. I am almost sure the wafers can be cleaned as well as the pockets they reside in. But for now i will wait..
I had been using an expensive Linn pre in place the l07c while try to figure this out...it is just not the same. The kenwood set is really something special. Thank you guys for taking the time helping me out. What a community!
You all have a wonderful new year!
Mark