PDP-11/73 boot issues

Aaron Jackson aaron at aaronsplace.co.uk
Fri Sep 24 17:01:36 CDT 2021

> Pete Turnbull via cctalk writes:
>> On 21/09/2021 20:34, Chris Zach via cctalk wrote:
>>> Can an MXV11 be used in a 22 bit system? I thought it was an 18 bit
>>> device?
>> MXV11-B is 22-bit.  MXV11-A is 18-bit but supposedly can be used in a 
>> 22-bit system if the RAM is disabled.
> Yeah this is a 22 bit card. Josh sent me an xxdp image which I could
> easily boot from my scsi2sd (thanks!).  Seems to be reporting an error
> with the CPU unfortunately:
> ]] .R ZKDJ??
> ]] 
> ]] ERROR # =001166
> ]] ERROR PC =040662
> ]] 043632
> This happens regardless of whether W9 is installed or not (supposedly
> disables the LTC register on the CPU?)
> I'll see if I can borrow another CPU card form a friend this
> weekend. Unless anyone else has any ideas?  Another suggestion on IRC
> was to disable the PSU LTC and enable the LTC on MXV11 but will need to
> look up some details on how to do this.
> Thanks,
> Aaron

Probing the BEVENT line and it was 50hz etc, but then I realised it
wasn't actually the right voltage. Replaced a transistor and now it


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