Malfunctioning VT240 - help please

[Charles]

On 6/11/20 3:15 PM, Mattis Lind wrote:
>
> The T11 is not halted - it's looping endlessly in the first ROM. There 
> is a brief burst of DRAM select activity on the scope just before it 
> hangs in the loop.
>
>  That burst of DRAM activity might indicate a DRAM problem. One thing 
> I have tried in the past is to put a known good DRAM on top of one 
> DRAM is the array. So to say in parallel. In the cases I have tried I 
> managed to make systems pass the memory check. Then test each and 
> every one in the DRAM array in the same way. Might be worth a try.
<snip>
>
> The 2681 https://www.nxp.com/docs/en/data-sheet/SCC2681.pdf shouldn't 
> be to difficult to configure and is located on the same bus as the 
> keyboard so you should be able to send something  on the UART to 
> either the printer/aux or the host.

========

Thanks again. I have some 4116's on order too. I'll try the piggyback 
trick, and if it works, will desolder the offending RAM (and install a 
machined-pin socket!) I will probably never have to change it again - 
but the PC board wouldn't like another desolder operation...

If that doesn't work, then I'll start writing diagnostic software using 
the 2681. Of course then I have to debug the program before I can debug 
the terminal ;)