Beta Lead input jack problems

[stumped91]

Hey I've been going off of a previous thread about input issues with Beta Leads but I thought I'd share my specific problem but I have a feeling it's in the same ballpark... When I plug into any input jack on my head the LED won't turn on and I have no signal, however when I pull the jack out about halfway, the LED turns on and I have sound but it's drastically quieter. I was hoping it might be as simple as adjusting the nut on the input but it's happening across the board which is a bit disconcerting. There aren't any particularly great techs for solid state amps that I know of in my city (Vancouver BC) and I was hoping I could have some direction to give to whoever I brought it in to lest they exacerbate the problem by messing around trouble shooting. If anyone's experienced a similar issue and found a solution or has a name of someone worth reaching out to in BC I'd really appreciate the advice! it's my favourite amp and I'd hate to have it break beyond repair
Thanks all!

[loudthud]

The inputs of a Beta Lead or Beta Bass use what is thought of as stereo phone jacks. The Switchcraft equivalent is the 12B. The three contacts are called Tip, Ring and Sleeve borrowing from old telephone jargon. When you plug in a mono phone plug, the kind normally found on guitar cords, the Ring contact of the jack is grounded to the Sleeve. Stomp boxes use the same idea to turn the battery on and off. A logic circuit inside the Beta amp detects this and turns the appropriate channels on. The same logic circuit allows the footswitch to control which channel is on if you are using the Both input. If no footswitch is connected, the circuit defaults to both channels on.

Your symptoms would suggest a problem with the power supply for the preamp. This is internal to the amp and needs to be serviced by a qualified technician.

[BassHog]

The Beta Lead heads use CMOS Logic chips for channel switching and controlling the muting and the lighting of the LED's.
I see a lot of Beta heads come in with these types of problems. There are CMOS inverter chips that control this along with a custom Boolean Logic chip.

I find that most often it's one of the Inverter IC's that have failed when the LED's are not lighting, this is part of the same path that controls the channel mute.
You can find these Inverter chips on ebay, there are a couple of different ones used depending on the year your Beta was made.
Hopefully it's not a failure in the Logic chip itself as these are much harder to find but you can still find people with them for sale if you search around.

I keep a supply of the Inverters in stock just for this reason.

This is not a DIY type of repair, you need to have a lot of experience servicing circuit boards and working with static sensitive components. It's very very easy to damage the circuit board when trying to remove the bad IC, and there are several of them so you need to be able to use a Scope and track the logic through the circuit to figure out which IC is not working.

[loudthud]

If the MC14506 chip is bad, there is a workaround.

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