[GreenKeys] Re: Dovetrons

[Doug Alderdice]

At 05:45 PM 2/12/2005, John Lawson wrote:
>   This is a fairly common 'gotcha' when connecting machines from 
> different eras to one another.  It's truly a bummer that you've had your 
> mobo scrambled - at least your machine's still basically functional and 
> the contents of your HD are safe.  I've had much more terrible results...

Yes.  I am thinking that I am lucky.

>   There is a line filter, sometimes called by the generic 'Corcom' but in 
> reality made by various companies, CorCom included. If this has broken 
> down it would tend to produce this fault, and it *would* be about 60Vac.
>
>   Also - is the Loop Supply bleeding to something? Or do you hev the 
> Tempest version with just TTL outputs, requiring a seperate loop-keyer.

This is the Tempest unit, one of the "Project Big Bird" batch that a number 
of us on this list got a couple of years ago.  It was not connected to 
anything else other than AC in and audio in.

>  If the problem persists, you can use a small 1:1 audio transformer of 
> suitable impedance to isolate the two ground systems....  but I'd sure 
> dig in and find out why the Dovetron is presenting such a solid leak 
> current in reference to it's internal grounds.

I am suspecting the EMI filter on the input of the power 
transformer.  Nothing else on the AC line in goes to ground, and Gil Smith 
mentioned yesterday that he blew a GFI breaker with his unit.  Sounds like 
we all better bypass that EMI filter.  I admit to not having a ground on 
the power cord I wired up for the Dovetron.  I knew it had the transformer 
for the power supply, so why bother with a ground for a quick test?  Errgh.

For now I am not doing anything with this Dovetron until I bypass that EMI 
filter.

73.

Doug, KA2WFT