From motherboard we can see that there is no user port and there is no place for MOS6551/8551 ACIA chip for serial communication, it uses 2x RAM chips IMS2620p-15 150ns 16Kx4 so giving total of 16KB ram, this board contain only 2x EPROMs 27128 ( 2x16KB rom) in total 32KB ROM. The P19 board uses essential same 32KB ROM, but in 3 EPROMs. One is 27128 (16KB) and 2x 2764 (2x*KB). From marking on P19 EPROM we see HI and LOW so content may be same. So depending of size of EPROMs you had you could populate 4×2764 (4x8KB) or 2x27128ROM (2x16KB) and mix variant as it is found on P19. And if we inspect board a little bit more we se 27128 and 2764 jumpers. As for missing IC in U4 this might be for 7400 or something related 7400~7432 (DIL 14 PIN IC) for either Commodore PROMs and/or adding more RAMs like 64Kx4 so it could been used as 32KB or even 48K system without some roms and with PLA addition 64KB did come to life. Fuses are also interesting, the board use two fuses, one seems to be fast and other one slow one. As for keyboard interface it is interesting that there is no SPI MOS6529 but only diodes used, in production they added the real thing for reading keyboard MOS6529.
There are two features that I like very much in this board first is normal joystick ports, second is normal expansion cartridge.
We do not know if lines were compatible with Commodore 64 ones, but there would be tons of cartridges developed that could be used ie second SID, and as cartridge is same as C64 , 3rd party developers would produce software and hardware faster.
Also international VIC 20 users could buy Commodore 16 with more colors and use it with joystick they already had and no mini DIN proprietary joysticks.According to source C16 TED Developer Alpha number P15 all ports and functions including EPROMs works and you are left with 12277 Bytes Free.
The empty ROM sockets are there because this board will either take 2764 EPROMs or 27128 EPROMs. There are jumpers to select 2764 or 27128. Andres board had a mix of 2764s and one 27128. I am not sure what the small chip socket is for.
We hope that with recent discovery it will be possible to fix also his younger brother P19 and make happy Anders Carlsson 🙂
Make sure you also checks link bellow, there are great pictures of TED Developer Alpha number P15 and some of P19 that you must see!
Parts of pictures above are borrowed to do analysis and to invite you to those sites 🙂
source:TED Developer Alpha number P15
source:TED Developer Alpha number P19