Zenith 3000-1 Question / Problem

[hth999]

I recently bought a Zenith 3000-1 on eBay a few months ago. It works well on all bands except the AM Broadcast band. I should say it's only a problem on a small segment of the AM Broadcast. I get wonderful sensitivity on most of the band, however at the lower end between 550-570 the radio goes deaf. When I turn the tuning knob I do hear strange static, ( like the tuning knob is causing the static ) so I am not sure what the problem is.
For example, I can tune all the way to the left, around 530 khz. ( we get a cuban AM station in FLA ) I get that okay, then I can tune up to 540, which I get sometimes, then after that the radio goes deaf, so 550-570 is deaf. But again I can hear static when I turn the tuning knob. Once I get to about 580 the radio springs back to life.( from 580 -1610 it's okay ) I can't figure out why. Does anybody have a suggestion ? I have used de oxit....pulled out the tuning knob and sprayed, didn't help. I have not removed the Chassis, because I don't think this is too big an issue for about 30 khz. All other bands work beautifully. FM is good, and so is any SW band. Any suggestions ?
Hal

 

[majoco]

Are you sure that the problem is only on the AM broadcast band? In theory it should affect all the AM bands at the same place on the tuning scale.Often with older radios a bit of dust or fluff will find it's way into the tuning capacitor - the thing that gets turned when you turn the tuning knob. Unfortunately in the 3000-1 it's quite difficult to get into to clean it. In the pic it's the thing with the vanes at the bottom right - from the front - so you have to get the whole chassis out of the case to see it. The bit of dust gets between the plates and shorts them together as you turn the tuning knob - and it moves so every time it is different. Disregard the red arrow, that was another problem! You can often dislodge the fluff with a thin piece of card in between the plates - all of them! With a bit of luck you may find that turning the radio upside down and turning the tuner may dislodge the fluff.

I wouldn't go spraying switch cleaner around indiscriminately - the coil formers and switch wafers soak up the cleaner and sometimes take weeks to dry out again - most people apply the cleaner with a Q-tip or similar. Also the scale drum is very delicate and some chemicals may take the print off!

If you decide to take the plunge I can send you the service manual or you can google for it. Just go very carefully and take photos as you go so you know where everything goes later!

Two words of warning - don't use a 12v wall-wart power supply - the radio takes so little current that the voltage may float up to 15volt or more and can easily pop the 12volt capacitor across the supply line - most people including me use a 9volt wall-wart - and the tip of the plug is NEGATIVE! It works fine.

..and don't pick the radio up by the handle! I know this sound stupid but after 40 years or so the plastic has become quite brittle and the handle will break in the middle with the waverod inside - especially if you have loaded it up wit "D" cells!

 

[hth999]

Thanks Martin,
I think you are 100% correct with the tuning capacitor. The only time there is a problem is when the 2 " plates " meet, which is the low end of the broadcast band. I think you are right, a bit of dust or something is between the plates causing the problem. I would never use de-oxit on them. I have sprayed a bit of compressed air on them, hoping to free up dust, but it does not seem to work. I have checked all the other bands, FM and SW...all seem to work okay except the AM Broadcast. I'm also aware of the handle. If I move it to another room I pick it up from the bottom. This unit has a good in tact handle / antenna, so I don't want to disturb it. Also, I would only use batteries. I have a good battery box with NO corrosion on this radio. Works well, and will last a very long time with batteries. I guess the only way is to take the chassis out....your right, it's very hard to get to the tuning capacitors, there appear to be 3 of them in order.
Thanks for your comments.....hth999 Hal

 

[Boombox]

I have the same problem on my 3000-1. It's the tuning cap. Some metallic crud or something must have gotten inside it. Blowing canned air did nothing. I'll have to take the radio apart to get to the tuner and see what is inside it, and then try to get it out. Which is why I've put it off. Good luck. There are instructions on the net as to how to remove the chassis on Zenith T-O's.

I'll second Martin's caveat RE power to the radio. I use batteries only. Anything over the required voltage will heat up the final transistors and your radio may go temporarily deaf. This happened to mine. Luckily, the transistors just got warm and shut down -- they didn't blow. Still works well in that department. After that incident, using a wall wart (required voltage, but wall warts often put out more volts than rated), I went to batteries only and have had no problems except the tuning thing.

T-O's are light on batteries, by the way. A set will last a long time.

Good luck in the repair.