Zenith 3000 Power Jack issue

[mcdmgb]

I have been slowly repairing a Zenith Trans Oceanic 3000-1 radio that was dead when I got it. I am in the home stretch of putting it back together, but have run into an odd problem. When I reattach the 12-volt power jack to the chassis and use the wall wart, the radio is dead. If I have the jack loose and hanging, it works fine with the wall wart. It appears to be some sort of grounding issue, but I'm not sure what I need to do.

Anyone run into this before?

Thanks

[liammc00]

Originally Posted by mcdmgb

I have been slowly repairing a Zenith Trans Oceanic 3000-1 radio that was dead when I got it. I am in the home stretch of putting it back together, but have run into an odd problem. When I reattach the 12-volt power jack to the chassis and use the wall wart, the radio is dead. If I have the jack loose and hanging, it works fine with the wall wart. It appears to be some sort of grounding issue, but I'm not sure what I need to do.

Anyone run into this before?

Thanks

If you could take a picture of jack I might be able to help.

[mcdmgb]

Okay, I'll try to get it posted tomorrow.

Thanks

[mcdmgb]

Photos attached. Obviously, I don't make my living by photography.

[Electronic M]

If the case is metal it is possible there was an insulative washer between jack and case and between case and nut your missing...they could have made jack barrel negative and case positive.

[jr_tech]

On mine, the sleeve of the connector is grounded to the chassis...0 ohms!
The red wire measures open/infinity to ground with the switch off and about 300 ohms to ground with the switch on.
I would check to see if perhaps the red wire is shorting to ground when the connector is mounted.

jr

[mcdmgb]

Originally Posted by jr_tech

On mine, the sleeve of the connector is grounded to the chassis...0 ohms!
The red wire measures open/infinity to ground with the switch off and about 300 ohms to ground with the switch on.
I would check to see if perhaps the red wire is shorting to ground when the connector is mounted.

jr

Apparently that was the problem. I reinstalled it paying attention to avoid shorts and powered right up.

Thanks much!

[Jeffhs]

I have three of these radios (one is a TO 1000-1, the other two are TO 3000-1s) and would like to pass along a cautionary note:

Be careful if you have to rewire the wall-wart plug (the one at the end of the wall wart's output cable that plugs into the jack on the side of the radio). Zenith, for some reason I have never understood, wired the wall-wart plug (and its mating jack on the side of the radio) such that the tip is negative, the barrel positive, exactly the reverse of how most wallwart plugs are wired. If the wall-wart plug is wired tip (+) barrel (-), you will damage several transistors and other components in the blink of an eye, or even faster. I'm sure the schematic diagram will show this. I am not at all sure (in fact, I have no idea) why Zenith decided to design the solid-state TOs of the '60s with these oddball AC adapter sockets; it seems odd, to say the least, for any radio made in the US.

[jr_tech]

Yep, positive ground, just like some older British automobiles. I suspect that a fair number of transistor radios that were designed incorporating PNP transistors were configured that way as a matter of design convenience.

jr