SX-42 AC on chassis

[k5ygc]

Measuring from earth ground the sx-42 chassis reading 89 vac with on off swith off or on. Line bypass caps are good disconnected gnd from filter caps and no luck. Check continuity from AF/on off switch to chassis nothing.Any ideas?

[ke7trp]

When you say earth ground are you talking about the power companie ground/neutral?  Or are you talking about a seperate ground in your shack? 

The first thing to try is to flip the leads on the power plug. Its possible its backwards or even backwards at your wall socket. 

Let me know what you find and a way to test is to hold the negative lead of the meter in your hand and the pos to the chassis of the radio.  If there is voltage there it will show up and you wont get shocked.

C

[k5ygc]

Seperate ground in the shack.Reversing the plug didnt work already tried that.Tried the negetive lead in the hand and was reading 29 vac that was with it plugged into the variac.Plugged it into the wall outlet and reads 18 vac.

[ke7trp]

So what I am trying to wrap my head around is that after you added the SECOND Shack ground to the rig, you got voltage on the case???

The rig should have a three wire cord on it with the correct polarity.  The Hot should run up to the on/off switch. You should have a fuse also. If you dont want to drill the hole, then mount the fuse inside. You would then remove the two bypass caps.

After this, You should see little to no ac on the chassis. 

I have measured the voltage from shack ground to rig and have seen voltage there. The consensus was that there is different potential from the shack ground to the house ground. 

[KM1H]

The original line bypass caps are paper and under the transformer cover on the bottom of the chassis. If those arent removed/replaced you will always have excessive AC leakage.

Replacements also have leakage but its at such a low current, if you dont exceed the NEC .015uF rule, that it wont harm you.

A 3 wire cord is the only way to go especially if not sure all your house wiring is correct...lots of electricians routinely reverse hot and common and dont bother confirming every outlet.

Carl

[KA3EKH]

You using a digital meter or an analog meter? Digitals are useless for such measurements, there may be a potential but it can have little or no current. Analog meters have lower impedance and will put a load between the radio and ground and provide a real indication as opposed to a high impedance digital meter, just a thought because it sounds like you checked just about everything.

[ke7trp]

Good point....

I am still waiting to find out if he has a three wire cord on the rig or just a two wire and hooked the shack ground to the radio.

C

[K9PNP]

Have the same issue with my S-85.  It has been that way since it was new in 58.  Even with the line bypass caps disconnected, have low current AC to ground.  Roughly the same voltage to either station ground or AC line ground.  The only thing I could think of is the power transformer has a leakage to ground.  I see on the S-42 that one side of the AC line goes to a connection on the power transformer that shows no internal connection.  Didn't replace the transformer to see if it is the issue since I want to keep the rig original since it was my original Novice receiver.

[WQ9E]

With the chassis ungrounded even with good quality bypass caps a meter with high input impedance is going to indicate an AC voltage  differential to ground and it is likely the transformer itself will have sufficient capacity to its case to transfer some AC to the chassis.  The proper measurement is leakage current-not voltage, see the classic Simpson 229-2 purpose built leakage current measurement instrument manual for more details on how to properly make this test (and there is a long standing UL standard for it):  http://www.simpsonelectric.com/uploads/File/229-2_manual.pdf

[N0WEK]

Two wire cord or three wire cord, the safest way to go is the old standard...The ground is the first thing hooked up and the last thing disconnected!

That said, any boat anchor I get into gets a new three wire cord first thing!

[k5ygc]

I added the 3 wire cord and solved the problem.Still have more hum in the audio than I think it should have.I replaced all the paper caps and resistors that were out of tolerance.Thanks for all the help K5YGC