After a long time I decided to fix all my Grundy NewBrain computers, starting with my very first one. It worked fine after recap, but after few years second memory bank stopped to work and in fact now the whole computer died.

After some measurements it's obvious that -5V is missing on memory chips. After a change of Zener diode [1] things a kind of improved, once I was able to check PRINT FREE in BASIC (to find out that only first memory bank is working) but overall the computer is still dead. Next step is to find out if one/some of the memory chips isn't/aren't broken and drying the voltage out.

Second repair session hopefully on Saturday.

#newbrain #8bit #grundy #repair