A TC-01 That Starts Up as an Einstein 256

The Einstein 256 looks like a TC-01 with a new badge, but it has a Yamaha V9938 video chip and 192K of video memory where the TC-01 has a TMS9129 and 16K. Owners of the original machine can now have much of the difference for themselves. Board-Folk's V9938/V9958 adapter, designed by Ian Cudlip, plugs into the TC-01's video chip socket in place of the original chip, and with the 256's own ROM fitted alongside it, a TC-01 switches on to the Einstein 256 start-up screen.

A Guide From Someone Who Has Done It Three Times

Adam Groome has fitted the adapter to three TC-01s, and has written the whole job up for the site in Build and Installation of the Einstein TC-01 V9938/V9958 Adapter: what to buy, building the board, getting the main board out of the case, removing the old video chip and voltage regulator, fitting the adapter, and writing the new ROM. He is honest about the risk. The TC-01's traces are fine and easily lifted, he damaged one himself on the way, and the guide has a full section on repairing a damaged pad or trace using the board's vias, with the method that got his machine working again.

At the end, a press of CTRL and P followed by RETURN gives full colour 80 column text.

Two Things the TC-01 Needs

Board-Folk found two problems on factory built TC-01s that did not show up on their replica board, and both are covered in the guide. The first is power: the original LM350T5 regulator overheats with the adapter fitted and cuts out, so it has to be replaced with a regulator rated at 1 amp or more; Adam used a Traco TSR 1-2450. The second is the ROM. The 256 has a port at 26h, for its Alph key, that the TC-01 does not, and the 256's MOS 2.1 reads it, so on a TC-01 Alph lock switches itself on and off. Board-Folk's fix changes three bytes of the ROM so that it no longer reads that port.

That patched ROM is now in the library as MOS 2.1 Patched for the TC-01 V9938/V9958 Adapter, prepared by Adam, ready to write to a 27C128 EPROM. We have checked it against the 256's own ROM: the three bytes are the only difference.

Where to Start

Ian Cudlip's notes on the board are in Einstein TC-01 V9958/V9938 VDP Adapter, and the Gerber files and bill of materials are on Board-Folk's GitHub. If you would rather write for the 256's graphics than solder for them, our Einstein 256 Primer covers the video chip, sprites, scrolling and the 80 column mode; it was written and tested on the 256 in MAME, and we have not yet tried it on an upgraded TC-01, so we would like to hear from anyone who does.

Thanks to Ian Cudlip and Board-Folk for the board, and to Adam Groome for the guide and the ROM.