My manual is beyond worn-out from reading, re-reading and referencing. Either I'm not stating the question clearly or you're not understanding it.
My problem is with the internal Effect loop. To apply, say, Delay, to a channel you highlight Delay from the Single Effect pop-up menu. You press "Yes" to confirm that that's the Effect you want. Then you press and hold the Single effect key (it lights) and simultaneously press and hold the "Select" key of the channel you want to assign it to (it lights, too; then both buttons flash).
I've done this a million times. Now, all of a sudden, it doesn't work. I can bring up the Effect menu, I can highlight and select Delay (or whatever) ... but when I then simultaneously press and hold the "Single" key and the "Channel" key ... nothing happens. It works fine with the "Mic Effect" and the "Multi Effect." But not with the "Single" effect. The procedure for assigning any of those three to a channel is identical, as you well know. So, I know I'm not doing this wrong. I'm just wondering if someone else has encountered the problem and solved it by ... I don't know ... prying the button up and sprinkling fairy dust under or something.
If this forum can't help, I will contact Tascam customer service.