DEC TU-80 Trouble shooting info

Tony Duell ard at
Wed Nov 22 19:40:39 CST 2006

> Hi Tony
> Yes, there is activity in the address lines at least.
> I would beleive is gets hung on something. I can see
> some activity for a breif period in different parts 
> of the board. like it was in self test. Then it looks
> like it gets hung. Not sure what type of a Processor 
> it uses, but watching the address lines on the roms
> it starts out Ok.  With all of the Error codes in the
> manual and none being displayed, It would have to be 
> a very low level problem. 

It would be worth identifying the processor...

My experience is that if a peocessor-based system gets really confused 
(as this one seems to be), then quite often the RAM or RAM control 
circuitry is to blame (for example if the stack can't be stored correctly 
in RAM, the system will go into lala land at the first RETurn 
instruction). ROM and processor failures, while also possible, seem to be 
a lot less common.

> As Dave pointed out, it's not a  true DEC item.  
> So with out much to go off of it would be a long up
> hill battle.  

Do the chips have recognisable numbers, or are they house-coded?


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