Sunn Beta Lead, no sound with "both inputs" input

[imgettingcloser]

At the thread title says, I have a Sunn Beta Lead that's not producing any sound when plugged into the "both inputs" jack. However, it works perfectly fine when plugged separately into either Channel A or B. Another thing I remember is that when I had my foot switch plugged into it, it would not switch channels and would only light up the red LED.

Any suggestions before I start working on it?

[loudthud]

Any suggestions before I start working on it?

Can you troubleshoot digital logic? The Beta preamp channel switching  uses CMOS logic running between ground and -15V.  Many people blame the MC14506 chip which is very hard to find.  What country are you in?

[imgettingcloser]

Yes. I should be able to do that.

I live in the US.

[loudthud]

Check this thread: https://forum.sunnstillshines.online/index.php?topic=6864.msg29374#msg29374

[imgettingcloser]

Any idea on where to even get the CD4011C? I tried Googling and couldn't find anything.

Actually ended up finding the part number on NTE. Which component carrier did you use?

[loudthud]

ICs in DIP packages are being discontinued because nobody is buying large lots. You can still find surface mount chips in SOIC.  CD4011 is an RCA number.  MC14011 is the old Motorola number (now ON Semi). Check places like Jameco or Parts Express.  They probably still have them in DIP. Dip component carriers are also getting hard to find and they are ridiculously expensive. Mill-Max wants something like $10. Aries 16-600-10 is one, Mouser stock number 535-16-600-10. Just use a machine pin socket and solder to the sockets.

Make sure the 14506 is bad. Check that you get a good low on pins 4 and 12 when a cable is plugged into the Both input. You should also have a low on 1, 2 and 10 and a high on 9, 3 and 11. You should also investigate the problem with the footswitch. If one of the LEDs blows, the footswitch will stop working. The logic levels from the footswitch inputs are not very good, marginal at best. This thread has info on footswitch troubleshooting: http://sunnforum.ampage.org/sdp/index.php/topic,6815.0.html

[imgettingcloser]

So, I just got done playing around with it some more before taking it out and testing the logic IC. When the it's a instrument cable is plugged into the "both inputs" section, it does light up both green and red. Also, when the footswitch is connected, it will switch like normal or do both channels. However, there is no sound through any channels when it is plugged in.

[imgettingcloser]

Tested the logic.

Pin 4 -13.97V
Pin 12 -14.01V
Pin 1 -12.66V
Pin 2 -12.66V
Pin 10 -12.68V
Pin 3 -00.1mv
Pin 9 -00.1mv
Pin 10 -00.1mv

So everything tested out. For a brief moment last night it started playing through both channels with the f/s functioning properly. Ended up finding that one of the input wires on the both input was a little loose and re-soldered. Now it is no longer producing sound at all. In either Channel A, B or Both. Frustrating to say the least. The test on the pins were after it stopped producing sound.

[loudthud]

Check that the -15V regulator is still working. The circuit is on the power amp board but plus and minus 15 are supplied to the preamp. It's easy to kill those regulator circuits.