[TowerTalk] Fwd: Grounding of tower

[Jim Brown]

On 5/10/2013 11:55 PM, Jim Thomson wrote:
> ##  Interesting enough, you won’t find  3 prong plugs on any consumer stereo gear these days !
> They are ALL 2 prong types, with a polarized plug.  Ditto with flat screen TV’s  etc.  If the
> chassis’ ever ended up hot, you would not be aware of it.

Those appliances manufactured without the third grounding pin are Class 
II appliances. Class II appliances are those that cannot present a shock 
hazard, either because they have no exposed metal parts, or because any 
exposed metal parts are "double insulated" from mains power.  Most power 
tools also carry Class II ratings.

> ##  Is anybody actually stupid enough to make pro-audio rack gear with pin 1 problems?

When Neil Muncy published his classic paper on Pin One in 1994, 
virtually ALL pro audio and broadcast gear was built with Pin One 
Problems -- it was hard to find anything that was done right. Ten years 
later, a tour of the exhibit floor would turn up lots of Pin One 
Problems, but also a lot of gear that was good.  Now, nearly 20 years 
later, MOST pro gear does NOT have Pin One Problems, but nearly all 
consumer gear, computer gear, lots of "semi-pro" stuff, and nearly all 
ham gear is still built with Pin One Problems.  The Pin One Problem was 
addressed by the first AES Standard on EMC, AES48.

> I have 2 full racks of pro audio gear, and none of it has pin 1 problems.   If it did,  I would
> just send it back.

I suggest that you carefully examine it, and perhaps do the RF Pin 1 
tests described in the AES paper on my website. It's pretty simple -- 
you drive between the shield and the chassis with an RF generator 
modulated by a 1 kHz tone and listen to the output of the DUT for 1 kHz 
as you sweep the generator from 100 kHz to 500 MHz (or whatever your 
frequency of interest). You repeat that test for every input and every 
output, and  if you hear the tone, you've got a problem. It's also worth 
looking at the connection of the power system "Green wire," which is 
often insulated from the chassis by paint.  That's a common problem with 
Astron power supplies.

> ##  On both my yaesu 1000MK-V’s and also the pair of 1000 –D’s,  I’m sure they both  have the
> pin 1 problem.  On the mk-v, the rca  patch input on the rear apron is a right angle to the board.
> No big deal, I just installed a new rca jack directly to the  AL rear apron....then wired the hot side of the rca directly to the analog BM input...problem solved.

That's the sort of thing that we have to do.  OR put a common mode choke 
on the cable connected to the Pin One Problem.  When I was using  
FT1000MPs, I had RF feedback through the mic jack on 75M and 15M.  A 
sweep with the generator showed peaks just above 75M and at 15M;

73, Jim K9YC