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scouter3d
August 21st, 2011, 10:29 PM
Hi,

The newbrain is not starting, i have replaced all the electrolytic capacitors on the mainboard => did not help
I even replaced the lower 16k memorychips => did not help

Using an oscilloscope, i found the following:

measured on the ZX80 at powerup:
the INT line is static LOW and not changing
at powerup the datalines start to work for about 2 seconds and then D3 stays High (as if the signal is shrinked to 0.5V and "added" to 5V)
BUSAK and BUSREQ are Low instead of pulsing
WR is not pulsing

I do have the shematics, but i am no expert in electronics, just a bit of basic knowledge picked up repairing my Vintage Computers ...

Any Help is Welcome!

pearce_jj
August 22nd, 2011, 12:03 AM
Firstly to say I have no idea about the specifics of this machine.

However, I wondered whether there is a 'power good' signal from the PSU, and if there is whether that is working. Also is the output from it stable enough, i.e. free of ripple?

scouter3d
August 22nd, 2011, 06:14 AM
Hi pearce_jj,

Thanks for your quick reply, the newbrain has an external PSU (+5, -12 and +12V) and an internal conversion to "stable" +5, -5, and +12V.
I have checked all the lines and they are good and without ripple.

Greetings TOM:-)

billdeg
September 3rd, 2011, 03:23 PM
Good luck, I hope you get it running. Where did you get the schematic?

Chuck(G)
September 3rd, 2011, 03:56 PM
I think this is Tom's Blow-by-Blow on another forum (http://www.newbrain.info/component/option,com_agora/Itemid,62/task,viewtopic/pid,93#p93/).

It might save some time.