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geojunkie February 15th 04 12:10 PM

Hot Chassis
 
I have an SX-71 in which I replaced the paper and lytic caps and still
have some stray voltage on the chassis. You can get a pretty good
shock under the right conditions. It was there before the recap and I
thought my resto work would have cured it. What could be causing this?
Also notice this on an older SX-16 that hasn't been recapped yet.

Dan

Chuck Harris February 15th 04 02:24 PM

Many radios have a pair of capacitors that go from each side of the
power line to the chassis. They are put there to prevent RF from
coming into/out of the power cord. In the best of conditions, they
put the chassis at 1/2 the power line voltage above ground. That is
low enough not to hurt you, but high enough to make the chassis feel
"buzzy" when you slide a finger across the metal.

Add a 3 terminal power plug/cord to the radio, and connect the green
wire directly to the chassis, and the tingle will go away.

-Chuck Harris

geojunkie wrote:
I have an SX-71 in which I replaced the paper and lytic caps and still
have some stray voltage on the chassis. You can get a pretty good
shock under the right conditions. It was there before the recap and I
thought my resto work would have cured it. What could be causing this?
Also notice this on an older SX-16 that hasn't been recapped yet.

Dan


k3hvg February 15th 04 06:17 PM

I'll confirm the other post. Looks like C60, a .01 600v cap is from one
side of a.c. to ground. I'd certainly suspect it being leaky. If you're
going to replace it, why not use a .01 at 1KV disk, instead. Good luck
with it... doesn't sound like too much of a problem. I'd recomend that
you add a 3-conductor line cord, too. It doesn't detract from the looks
and its a heck of a lot safer!!! de K3HVG

geojunkie wrote:

I have an SX-71 in which I replaced the paper and lytic caps and still
have some stray voltage on the chassis. You can get a pretty good
shock under the right conditions. It was there before the recap and I
thought my resto work would have cured it. What could be causing this?
Also notice this on an older SX-16 that hasn't been recapped yet.

Dan



N4BUQ February 15th 04 07:03 PM

....or take those caps out and install a modern line filter somewhere outside of
the chassis.

Also, if you do install a third ground wire (which I DO recommend), you won't
be able to power the radio on a circuit that is protected with a GFI (Ground
Fault Interrupter). It'll pretty much pop the GFI every time.

Barry - N4BUQ


Uncle Peter February 15th 04 08:17 PM


"N4BUQ" wrote in message
...
...or take those caps out and install a modern line filter somewhere

outside of
the chassis.

Also, if you do install a third ground wire (which I DO recommend), you

won't
be able to power the radio on a circuit that is protected with a GFI

(Ground
Fault Interrupter). It'll pretty much pop the GFI every time.

Barry - N4BUQ


You are kidding, right? If there is that much leakage current, then the
problem should fixed before adding the three wire line cord. There
is no reason to pop a GFI.

Also, the maximum value for the bypass cap, which should be UL
rated, is about .015 mfd.

Pete



Frank Dresser February 15th 04 08:25 PM


"N4BUQ" wrote in message
...
...or take those caps out and install a modern line filter somewhere

outside of
the chassis.

Also, if you do install a third ground wire (which I DO recommend),

you won't
be able to power the radio on a circuit that is protected with a GFI

(Ground
Fault Interrupter). It'll pretty much pop the GFI every time.

Barry - N4BUQ


I don't see why it will pop the GFI unless the line bypass cap is
unreasonably large or something is leaking current. I've done the 3
wire cord modification to a few radios and most of my test equipment,
and I haven't had that problem.


Frank Dresser





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