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 Post subject: Re: Zenith TO 3000-1
PostPosted: Dec Tue 13, 2011 10:03 pm 
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Location: Halfway between Possum Trot and Monkey's Eyebrow KY
ON mine I had to replace the transistors in the AM portion as they all were bad. I tried bending the ground pin as well but they were just bad.

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 Post subject: Re: Zenith TO 3000-1
PostPosted: Dec Wed 14, 2011 12:31 am 
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Location: Sunnyvale CA
simplex1040 wrote:
ON mine I had to replace the transistors in the AM portion as they all were bad. I tried bending the ground pin as well but they were just bad.


Yeah, the ground pin is only one of the possible failure modes just from tin whiskers, not to mention the other possible failure modes. I ended up replacing all 3 IF transistors in a Royal 1000 recently, and the mixer in a Royal 3000. Fortunately, as near as I can tell, the NTE replacements work just as well at least in these spots, and are widely available. I have two places within 3 miles of my house that sell them right off the rack.

In this case, I would have to check the cross-reference gadget, but I think the NTE 160 is the replacement for all three of the suspect transistors. It might not work as well as the original RF transistor but it will function. I think the original is an Amperex 2N2089 which is a little tricky to find and expensive, being used (wasted?) in some relatively famous guitar amp noise gadget.

Brett

p.s. I checked my service manual and the three radios I have in hand, and they aren't all the same. One version has RF = 121-44 (2n2089)
which is a lot like the early Royal 1000, and I think that wants an NTE 126 as a replacement. The other version uses a 121-349 which is replaced by an NTE 160. I may not get a chance tonight but I will check for sure which one works with which. In both cases the Oscillator and Mixer can be replaced with an NTE 160. I have noticed a big alignment shift when I replaced the oscillator with either an NTE 160 or a different 121-350.

p.p.s. I was too curious not to drop everything and try it. That's really more of a personal problem...

In the three radios I tried (two Royal 3000-1s, 12kt40Z8 and one Royal 1000 , 9CT41Z2)
In all cases, it worked with and NTE 160 in the Oscillator and Mixer positions
None of them worked with one particular NTE 160 in the RF position and appeared to oscillate. But a DIFFERENT NTE 160 did work in the Royal 1000 as an RF transistor, and not the others
An NTE 126 worked in the RF for any of the three radios
An NTE 126 worked in any of the other positions as well.

So I recommend that to maximize your chances, use an NTE 126 in the RF position, and an NTE 160 as an oscillator or mixer. You *could* use 126s in all three positions but an NTE 160 is about half the cost. And they are all very expensive compared to any modern transistor - and NTE 160 is about $5 and an NTE 126 is about $10. Compared to a double handful of any common NPN MOSFET for about a $3.

Earlier, I suggested that (probably based on having done the above test before) that it wouldn't work with the Mixer or Oscillator transistors in the RF socket. So I tried that, too, and in all three cases, it at least played something with the transistor swapped around.

Note that when I say "worked" in any of these cases, I mean it picked up a moderately weak BC band station in the 3 seconds I tried it. I didn't check the sensitivity or check any of the higher SW bands. Based on previous experience the NTE replacements seem to work about the same as the original Zenith or EIA parts as long as you redo the alignment. An NTE 126 even works just fine in the FM RF position at 108 mhz. and the NTE 160 works fine on FM in the IF section at 10.7 Mhz. Other people have had other results, and I haven't been particularly picky or tested the sensitivity carefully.

I have also used an NTE 160 as the 1st AF and driver positions. It got hot in a few seconds but it worked for a little while. It would fail quickly if you left it. Those should really be NTE 102As that can handle the current. Point being that one NTE 160 and one NTE 126 can be used effectively for troubleshooting failed transistors for any of the positions as long as you don't do it for long. Once you know what is failed, then you can be more careful with replacements.


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 Post subject: Re: Zenith TO 3000-1
PostPosted: Dec Wed 14, 2011 8:29 am 
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Location: Sunnyvale CA
tagski wrote:
Hey evryone, I tried bending the shield pin on both transistors and still the same, FM works good, all other bands nothing.
George


You say "both", but there are three of them that might be bung.

If you can't get them easily in your area, PM me your address, and I will send you some NTE replacement transistors (2 NTE 160s and a NTE 126) to test with. All I ask is that you report the results here, and that you send them back or replace those that you use.

If it's not the transistors or the bandswitch, it's approaching the limit of what I can troubleshoot over the internet, or without a signal generator. In this case the symptoms (FM works) preclude almost all of the other obvious problem areas. The other moderately common problem component are the electrolytic capacitors but I don't think any of them in this radio are unique to AM. There are many hard-to-reach little ones up behind the dial drum but all but one of them (C35, 10 mfd/6v) is associated with the FM IF strip and discriminator, as I recall. The others are on the power supply and audio both of which are obviously working, at least well enough to tune in stations.

Another item suggested by your symptoms is that the antenna is not connected. Might want to inspect the wires going into the back of the BC antenna connector. It's possible that the BC antenna is bad or has a bad connection, and you don't hear anything on SW because there's nothing on SW that you can receive whenever you have tested it. If you had one, or I had the radio here, I would fire up my signal generator and set it to the middle of each SW band and see if I hear it, and also test the IF frequency. It's at least remotely possible that the FM IF strip is OK, the transistors are OK, but there is something wrong with the AM IF transformers or the disc caps. That would be rare but not out of the question.

Brett


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 Post subject: Re: Zenith TO 3000-1
PostPosted: Nov Tue 26, 2013 2:40 am 
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Can someone help me to identify those two small square plastic parts that I found on a bottom of chassis of Zenith Trans Oceanic 3000-1 after it was disassembled.

Where they are from?

Trying to preserve radio as much close to the original as possible.

Thank you for your help.
Sincerely,
Paul


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 Post subject: Re: Zenith TO 3000-1
PostPosted: Nov Tue 26, 2013 5:34 am 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 3595
Location: Sunnyvale CA
pnimitz wrote:
Attachment:
plasticpart02.jpg


Attachment:
plasticpart01.jpg


Can someone help me to identify those two small square plastic parts that I found on a bottom of chassis of Zenith Trans Oceanic 3000-1 after it was disassembled.

Where they are from?

Trying to preserve radio as much close to the original as possible.

Thank you for your help.
Sincerely,
Paul


They are some sort of high-density rubber - that is now the same density but more like rock. They are there to keep the battery box from rattling around in the back. I haven't found a good source for the material but some very dense foam rubber would work. Mine have all long since fallen out and I didn't bother replaceing them.

Brett


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 Post subject: Re: Zenith TO 3000-1
PostPosted: Nov Tue 26, 2013 7:11 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10457
Location: Mpls, Minnesota
Here is my listing for the TO's

Image

Dave


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 Post subject: Re: Zenith TO 3000-1
PostPosted: Jul Wed 16, 2014 7:39 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 486
Location: Saskatoon,Sk.,Canada
I just repaired a Zenith 3000-1.Original symptoms were no AM and very weak FM reception.I found both the 1st IF transistor and the 2nd IF transistor had ground whiskers.I was lucky in that I bent the ground leads out of the way and the radio worked great
Jim Frey


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 Post subject: Re: Zenith TO 3000-1
PostPosted: May Fri 19, 2017 9:04 pm 
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Joined: Jun Fri 24, 2016 5:07 pm
Posts: 28
Location: Louisville, KY
Could having whiskers on the transistors cause distortion on all bands? The audio gets loud and seems to be fine and the tuning is spot on but all bands have distorted Audio.


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 Post subject: Re: Zenith TO 3000-1
PostPosted: May Sun 21, 2017 1:18 am 
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Joined: Mar Mon 27, 2017 4:29 pm
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"The audio gets loud and seems to be fine and the tuning is spot on but all bands have distorted Audio."

Brett, our Zenith expert, posted about this somewhere in this forum (you could try to search Zenith distorted audio). As I recall, he said this meant a transistor in the audio output stage. I will try to dig up the post.


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 Post subject: Re: Zenith TO 3000-1
PostPosted: May Sun 21, 2017 1:20 am 
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Joined: Mar Mon 27, 2017 4:29 pm
Posts: 29
I found the post:

viewtopic.php?f=4&t=318784&hilit=transoceanic+distorted+audio

Here is the summary:

low volume or hiss, but no distortion - 1st audio or driver
low to normal volume with lots of distortion - output transistors


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 Post subject: Re: Zenith TO 3000-1
PostPosted: May Sun 21, 2017 1:33 am 
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Location: Black Hills, SD 57745
This thread rocks and needs to be a sticky or pinned. The transistor TOs come up all the time. You could dredge up the old threads, but Brett has supplied such a nice annotated guide it needs to stay on top and we can just point to it.

One niggling item not mentioned is one that happened on my TO-3000-1. The shaft of the bandswitch is only crimped to the contact wafers. Or maybe it was the detent ring that became loose. Either way, If you watch closely while slowly rocking the bandswitch knob, you'll see the shaft move a bit before the contact ring follows. Thus, the detents no longer hold the shaft at the point where the contacts are, due to this slop.

If you can slightly rotate and hold the bandswitch and things come to life, that's a dead giveaway. Another good clue is you can rotate the bandswitch knob and it travels a bit before anything happens. This could also be a loose set screw holding the knob, but in that instance the contacts and detents will still align.

On mine the simple cure was to solder the shaft to the slipping crimps with things aligned so the contacts and detents are both in the right position. You can do this by rocking it one way or the other and backing up just enough to align the assembly. Then solder the crimps in a couple spots or use your own methods for securing the two.

It was so long ago, I don't recall how or where I got that soldering iron in that rat's nest to solder the shaft itself. I recall having to solder a couple spots along the shaft to hold things. Must be I had it out of the cabinet at least. I've never had to redo it since, but before, it would never stay in the sweet spot and I always had to nudge the bandswitch knob or it would go dead if bumped or changed.

What causes it is somebody forcing the knob past the last band up or down. Something's gotta give over time. Kids like to spin knobs, or just wear and tear.

Not a problem in the OP's TO, since his FM works. But here's one last tip. What some folks may not know, is one of the FM IFs has two ferrites in the same coil. One above and one below the chassis line. You need one of those diddle sticks with a slim shaft and shorter hex section to adjust each slug separately. Or align it with chassis removed. I'd get the special diddle stick.
-Ed


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