[cctalk] Re: Rainbow H7842 PSU Fault

[Paul Koning via cctalk]

> On May 1, 2023, at 6:23 PM, Brent Hilpert via cctalk <cctalk@classiccmp.org> 
> wrote:
> 
> On 2023-May-01, at 2:25 AM, Peter Coghlan via cctalk wrote:
>> It seems a bit odd that a power supply from someone like DEC of that era 
>> would
>> be designed to depend so critically on the absolute value of a rail used
>> for startup purposes.
> 
> Further to Peter's point above, the 1988 NatSemi databook - which is to say, 
> from the era of this power supply - specs the 7812 output min-max to be 11.4 
> to 12.6V (+/-5%). Your measured Vstart=12.4V is well within this.
> Looking at the schematic, nothing stands out where the distinction from 12 or 
> 12.1 would matter.

The usual DEC spec for power supplies was +/- 5%.  In reality there 
occasionally were issues: FS told me on one occasion when we had DMC-11s not 
working right that those actually need +5%, -0%, and that FS people knew this 
and would adjust power supplies as needed.

        paul