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Old 9th March 2011, 07:34 PM   #11
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Can you perhaps tell us which model Marantz this started life as, and then we'd have a sporting chance of finding out how it was originally wired. Even in the 70s I think there were few products supplied with one side of the mains intentionally connected to chassis. This is sounding slightly incredible.
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Old 9th March 2011, 07:45 PM   #12
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No, the unswitched outlet is also two-prong, (presumably) one being hot and the other neutral. I took the one that was connected to the case to be the neutral because it was shorted to the other (switched) outlet and because I, so far, have lived to tell the story. The AC voltage from the case to the metal trim on my kitchen counter is 0V and while I haven't played around with reversing the plug and measuring, I haven't always plugged it in the same way while using it either, and I haven't been zapped yet. I do intend to replace this mess with a proper IEC plug. I won't have the outlets any more, but I never use them anyway.

Upon reflection I wonder if I've been saved from becoming fried bacon by the fact that the current has an easier path to ground through the transformer - either by means of the on switch or (if the switch is off) the small cap across the switch.
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Old 9th March 2011, 07:49 PM   #13
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Not sure...I have a 1973 vintage Marantz 2230 and it is not wired the way you describe - on plug-in you have a 50% chance that the chassis is hot assuming the plug is unpolarized!
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Old 9th March 2011, 07:50 PM   #14
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Huntingdon, I'll check the model when I get home and post. I've gutted a few amps to reuse the cases (about six I think) and I've never seen anything like this.
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Old 9th March 2011, 07:52 PM   #15
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Quote:
Originally Posted by schubert View Post
The AC voltage from the case to the metal trim on my kitchen counter is 0V and while I haven't played around with reversing the plug and measuring, I haven't always plugged it in the same way while using it either, and I haven't been zapped yet.
This sounds even more incredible; the 2 prong plug is UNPOLARIZED and one wire was connected directly to chassis? I'd have to agree with Huntingdon, this is just too incredible. I'd say this can't be true, there must be some error in your decription or what you are assuming is the stock Marantz wiring.
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Old 9th March 2011, 07:58 PM   #16
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Believe me, I'm quite mystified myself!!! It certainly looks like stock wiring - the connections all look the same and mass-produced. There's a small protrusion in the case that appears to have been put there specifically for this connection. There's no doubt about the connection or the fact that the case isn't live, and I just can't figure it out.
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Old 9th March 2011, 09:21 PM   #17
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Quote:
Originally Posted by Huntingdon 361 View Post
Can you perhaps tell us which model Marantz this started life as, and then we'd have a sporting chance of finding out how it was originally wired. Even in the 70s I think there were few products supplied with one side of the mains intentionally connected to chassis. This is sounding slightly incredible.
Well, this unit spent its childhood as a Marantz SR-325 stereo receiver from 1984-85. I cursorily looked around for a schematic/service manual but couldn't find a free one.
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Old 10th March 2011, 12:06 AM   #18
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One thing I considered was that there was a 1M or so resistor in the sleeve, but I measured the resistance between the input wire and the case and got the familiar "beep" from my DMM indicating a short. Now I'm wondering if I was accidentally shorting my meter some other way, for when I measured the AC volts between the poles of the unswitched outlet I got 120V, but only 19V between the hot pole and the case, and 1-2V from the neutral pole to the case, depending on whether it's switched on. Sooo....there must be a resistor in there. Now I'll take it apart and find out for sure.
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Old 10th March 2011, 12:16 AM   #19
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Yep....carbon comp resistor, 2.2M. I guess that explains things.
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Old 10th March 2011, 12:52 AM   #20
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The AC voltage from the case to the metal trim on my kitchen counter is 0V...............
You need a decent ground reference for troubleshooting....either a proper earth ground at your workbench (direct connection to good ground rod) or (better) a connection to the ground of your AC house supply.
'Cheater' plugs assume that the wall box is grounded and connect to the faceplate screw...so that is one place to look.

With 'modern' plumbing, it's not a sure thing that you can get an earth ground from a plumbing connection - too many ways that you can get a plastic 'break' in the line, IMO.
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