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#26 25-09-2011 20:45:24

scouter3d
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Re: Broken NewBrain Help needed!

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:-)

 

#27 26-09-2011 20:17:34

Saphir17
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Re: Broken NewBrain Help needed!

Hi Thomas...

I don't know what versions the ROM's on the Dutch webpage is for, regarding circuit board rev.

It could be nice to know that ROM's works with what hardware or is it simply the newer the better... ?
If someone have the knowledge of that, please, let us know....

You have my permission to remove my ROM's and take a copy of them.

br
Michael


Aarhus, Denmark
NewBrain's: Model A & AD, ExpansionBox, DiskController + Drives, ROM-Box
 

#28 28-09-2011 12:37:59

scouter3d
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Re: Broken NewBrain Help needed!

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:-)

 

#29 28-09-2011 19:04:15

Saphir17
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Re: Broken NewBrain Help needed!

Hi Thomas...

Hmm... well there you go.. smile

Kluder actual mentioned to me in the beginning of this post, that he once have had some trouble with the IC421.

It could be fun to know if the LS245 actual "works" or is totally defect.
The LS245 is capable of 15mA in high state and 24mA in low, so actual a pretty rugged chip.
It's speed is measured in a few nS, so it also plenty fast and timing at 4MHz should not be a problem.

The load seems to be a IC420, the RAM (both typ. 0.1mA/input) + a 4.7K pullup (1.1mA) ...not something that can blow the LS245.

Ok.. You still need to get the full 32k RAM working smile

br
Michael


Aarhus, Denmark
NewBrain's: Model A & AD, ExpansionBox, DiskController + Drives, ROM-Box
 

#30 29-09-2011 17:32:06

scouter3d
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Re: Broken NewBrain Help needed!

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:-)

 

#31 29-09-2011 22:42:00

Saphir17
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Re: Broken NewBrain Help needed!

Hi Thomas...

Yes, sounds as a plausible explanation.
One for the books...

Congratulation with you working NewBrain.

best
Michael


Aarhus, Denmark
NewBrain's: Model A & AD, ExpansionBox, DiskController + Drives, ROM-Box
 

#32 24-10-2011 20:06:13

scouter3d
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Re: Broken NewBrain Help needed!

Hi,

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

Greetings TOM:-)

 


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