Some variants of the CD4013 that people have been using seem to stall or at least go into an always on state if the gate signal is > 5v. This shows itself as the accent always being on, and the decay knob not adjusting the envelope.
You can solve this by attenuating your gate signal to ~5v, but if your gate trigger is sending > 5v signals and you want to have a permanent fix, then a small tweak to board pre version 1.6.3 allows the signal to be attenuated on board.
You will need a 4.7v Zener Diode – such as a 1N5230B (Mouser part : 78-1N5230B).
You need to cut the existing trace between the Gate Input jack signal pin and pin 11 of the CD4013. You can either cut this close to the gate jack itself, or close to the CD4013, the pictures below show the trace. Note that depending on your PCB version, the trace maybe like the board layout CAD picture below – or like the photos.
In all cases the pictures below show lime green marks where we’d recommend you cut the trace – note only one cut needs to be made, so pick the one you feel is easiest for you to cut. Make sure you only cut this one trace!
Then make your own trace basically, with the 1N5230B diode inline between the two points. The black band should be facing away from the Gate jack pin, towards to CD4013 as shown in the picture.
Ge0sync Synth 
One response to “TB-EFA 5v Gate Fix”
[…] May 2023 – Decay pot appearing to do nothing? – For those that may experience an issue with the decay pot, seemingly having no effect on the envelope/sound. It has been found that sending a gate signal > 5v can result in some variants of the CD4013 IC entering a state where it defaults to “hi” output – i.e. the accent is always on. This in turn removes the decay control from the envelope which reduces the sound tweaking potential. A revision has been made for the next batch of PCBs, starting with v1.6.3. In the meantime a work around if you experience this is to attenuate your gate signal or to try a different gate generator that sends a ~<5v gate trigger. If you want to make a permanent fix to your PCB then we outline the modification here. […]
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