Question about 2 prong power cable on a Sansui 990DB Stereo

[DrGonz78]

So I am currently cleaning up a working Sansui 990DB stereo receiver and have a question in regards to the 2 prong power cable. It is not a polarized cable but it does have a white stripe down one of the wires. I don't usually work on too many stereo receivers so some of my questions will seem very newbish. Looking at the schematic there are EU and US versions of the AC power wiring. The unit I have has a 220v sticker on it's side and there is a 120v selector box. If you look at the attached schematic image you will see the US version has the two extra AC sockets but the EU version does not. The version I have seems to have cobbled the EU and US versions together since I have the switched & unswitched AC sockets.

My question is should I replace the 2 prong with another 2 prong that is polarized, will that be enough? Or should I put a 3 prong with a ground connector? I don't understand the US version with the 3.3M resistor to chassis ground and usually we see a death cap in that position. The AC wiring on the back of this unit is really hard to trace out but I will have to look at it a few more times. If I install a 3 prong cable are there any components that need to be removed? Any thought on these matters will help greatly, thanks.


The service manual can be found here if needed...
SANSUI 8080DB 9090DB 890DB 990DB AM-FM STEREO RECEIVER Service Manual free download, schematics, eeprom, repair info for electronics

[DrGonz78]

Not a lot of people interested in old Sansui receivers? LOL. Was just looking for opinions on what would "you" do? I have become use to the idea of installing 3 prong plugs on amps for guitar, bass, etc. In this case I could at least put a polarized plug on the receiver but the switch is on the opposite pole to the fuse. If I were to wire it would the hot side go to the switch side? I could just examine the wire and let the customer know that white stripe is hot or neutral, so he can plug it in with correct orientation. The easiest solution is the best in this case since installing 3 prong will be a bit more work(time cost is a factor).

Edit: Just to mention there is a ground cable connection that can be plugged into this device. Can adding the grounded 3 prong actually interfere with the way the amp was designed?

[SpareRibs]

Hello,
Regardless of anything else you do install the three prong plug !!!!!!!!! Use the ground connection as the ground for the three pronged plug. I don't know the answers to your more technical questions however, just by the fact you are talking about 120 or 240 makes it much worse than usual.
Maybe someone else will chime in, but I am sure they will agree with the three pronged plug as the first step.

[52 Bill]

I would probably replace the plug with a polarized one so that the neutral side connects to the chassis side. Rewiring it for a three wire with a ground is good, but there is limited risk involved as there not much contact with the grounded chassis during normal operation.

Guitar amps put the ground connection directly in contact with the player's skin all of the time. Home receivers not so much.

Just my 2 cents.

[Chuck H]

Like Bill said^^^^^^^^^^^^^^^^^^^^^

There's a slim possibility that something about the circuit will ground loop with the polar plug and chassis ground. Noise in these devices is sometimes worked out in tiny resistive increments. That's probably why it's not chassis grounded now. With multiple units in play the chances of a ground loop go way up. I've had to solve for this a few times with home systems from that era where interfacing wasn't well understood and standards were a little loose. It'll probably be fine. Do install the chassis ground and do make the neutral the 0V association and it should be phased with everything else that's done correctly.

[DrGonz78]

Thanks for the advice ya guys! I think I will go the extra mile on this one and just stick to the 3 prong cable. I am sure the customer will not mind the little extra bit of money for a bit of extra safety!! Honestly though I don't think many people out there working on these 1970's receivers even bother. Like Bill said the risk of shock is not as prevalent as with guitar amps and such. All your answers/opinions are greatly appreciated, thanks.