I have replaced the battery clip with one that doesn’t have the pp3 clip on it, to save space. I unsoldered the old one, and soldered in the new one, knotting the cable as cord relief, as per the original. I can now get the battery holder in and out easily.
I also got the chance to test the tc5501p – there is no output on pins 12, 14 or 16. So maybe a dead chip. New one is already ordered. Need a new 22-pin socket, too. More soldering. Yay!
Updated the thread here: http://music-electronics-forum.com/t45560/#post472977