The Newbrain Forum

Hi Michael,

I checked IC421 and i have activity on RD/ and on the data pins for a few seconds ...
I think the machine freezes at the time it tries to initialize the TV screen.

I checked IC402,3,4,5 there is activity on ROW but no activity an TVAD (tracing the TVAD back i found it is generated using BOL and as BOL stays miracoulously HIGH ...)

tomorrow i will start resoldering all joints and in the process i will socket the ROM´s and EPROM´s so i can try to burn new ones ...

Thanks TOM:-)

Hi Michael,

THE NEWBRAIN IS WORKING AGAIN!!!!!!!

I socketed all the Roms and Eproms (on both machines) and tested my Roms in your board, and they where all OK!

Today i replaced IC421 (74LS245) the Databus Buffer => And the NB booted instantly!!!!!!!!!!!

I also replaced 1 faulty RAM Chip an the Memoryboard and now everything is working again!!!

now i have to remove the headers again and solder in the old flatribbons ...

i hope i can fit the Ramboard (because of the sockets) or i have to remove them too and solder the chips directly ...


THANK YOU VERY MUCH FOR YOUR GREAT HELP

TOM:-)

Hi Michael,

After replacing the rightmost Memorychip, i have full 32K again!

The IC was pretty much corroded (from a nearby leaking capacitor) ...

So maybe: The capacitor leaked, the ramchip corroded - got shorted and IC421 blew ...

I removed the Flatribbons and fitted everything back in the case, this was a little hard because of the sockets, but it did fit ...

So: Operation completed!!!

Thanks TOM:-)

Hi,

I put up a few pictures of the repair here: http://www.8bit-homecomputermuseum.at/r … brain.html

Greetings TOM:-)