General > General Technical Chat

Consumer VHF-UHF receiver measures 100vac from chassis to ground

(1/2) > >>

videobruce:
I have two similar scanning receivers (Radio Shack Pro4004 & Pro2006) of similar design that I just discovered both have a 'hot' chassis. Measuring 100vac (no load) to earth ground (grounded roof antenna). It's a non-grounded line cord.
They both have a 'old school' power supply (metal enclosed xformer), not switching that is mounted to the metal chassis. There is a 1.8 meg resistor from the neutral to the chassis. There is no other component between the AC line cord and the xformer.  They were designed in the late 80's by GRE and were very popular.

If I de-solder the resistor, the leakage voltage drops to 9vac. So the question is, is it ok to leave it disconnected? I assume the 1.8 meg resistor is to drain any static charges off the chassis .

The odd thing is I have had one of these for probably 30+ years and never noticed this which I did now by re-connecting the antenna cable and holding a external metal enclosed FM broadcast filter and the antenna cable connector.

Tomorokoshi:
Is there a schematic for this thing anywhere?

tom66:
Looks like you have swapped L/N in your socket or cable somewhere.  (Or is that the reversible American cord that has no polarity?)

1.8Meg to chassis is probably not an issue.  Leakage current is <1mA.  But may be worth testing that.

videobruce:
It looks like that is/was the problem.  :(

BrokenYugo:
That's typical, no need to disconnect anything. The 66 microamps you'll get if the outlet is wired wrong aren't going to hurt anything or one. A couple orders of magnitude off from tripping a GFCI. Modern switching supplies and metal cased 2 wire equipment will show similar leakage if you go measuring them.

Hot chassis, strictly speaking, is when one side of the mains is directly connected to the chassis, mostly found in series string table radios from the 30s.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod