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 Post subject: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Thu 12, 2012 11:29 pm 
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Joined: Jan Thu 12, 2012 11:03 pm
Posts: 9
I'm new to these fourms, so I'll keep it short and sweet. My dad has a trans-oceanic 3000-1. The last time he used it, he tried using the external power jack. Sadly, he got the polarity reversed and killed it. He had no idea where to start. He said he would give it to me if I help him figure out the problem. We swapped all the transistors in another T/O he got, but the numbers on the transistors don't match. They all seemed to work, but the audio transistors seemed distorted in the other T/O, and got hot. Me and my dad finally thought we narrowed it down to the oscillator, due to we could not swap it with the other radio(the killed one has 4 pins, and the working one has 3 pins), and we tried to use another radio to pick up the signal from the oscillator, but we could not. My dad collected the voltages from the test points on the killed one and got as followed:
FM AM
1:-0.61 1:-0.61
2:-0.51 2: 0
3:-0.51 3:-.36
4: 0 4: 0
5:-0.20 5:-5.40
6:-0.20 6:-3.89
7:-0.28 7:-3.89


The radio makes a slight pop sound when turned on, and the dial light works. We ran an audio signal into the tuner output and get sound out of the speaker. Any help is appreciated


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Fri 13, 2012 12:51 am 
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Joined: Feb Thu 24, 2011 1:29 am
Posts: 3021
Location: Dallas, TX - in the city but with bobcats and coyotes
Service data here:
http://www.transoceanic.nostalgiaair.org/pics/r3000sm.pdf

Expected voltages for the seven test points are listed in the service manual.

It is also possible that the electrolytic filter caps failed when reverse biased. However, getting audio is a sign that they may well be OK.
Do both AM and FM fail? If so, there is a section in common to both modes that would be suspect.

_________________
In a triode, no one can hear you screen.


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Fri 13, 2012 2:12 am 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 2444
Location: Sunnyvale CA
mescalero wrote:
Service data here:
http://www.transoceanic.nostalgiaair.org/pics/r3000sm.pdf

Expected voltages for the seven test points are listed in the service manual.

It is also possible that the electrolytic filter caps failed when reverse biased. However, getting audio is a sign that they may well be OK.
Do both AM and FM fail? If so, there is a section in common to both modes that would be suspect.


I did something similar but mine "recovered" after a few hours of just sitting - presumably because I didn't quite kill the backwards-voltaged capacitors.

I would strongly suspect the electrolytic caps across the power supply. They're easy to get to, and the two likely candidates are right under the opening in the chassis where the speaker goes through. And definitely check the voltages on FM and AM.

The part numbers are in the service manual but if you check this post:

viewtopic.php?f=6&t=180886&hilit=+royal+3000

you will find some of the variations, and some of the NTE equivalent part numbers. It also has the corrected voltages (there's an error in the service manual). If it's just AM/SW that has the problem you can use the data in that post to troubleshoot, as well. If it's both FM or AM, I doubt that it's the oscillator (since it would be two separate oscillators), it would almost have to be the IF transistors or maybe the first AF (check the schematic and see if the external audio is tapped before or after the first AF stage).

I have made many various "oopsies" with 60-s style bipolar transistors over the years and I would be a little surprised of 12v the wrong way actually blew any of them, but it's possible.

Brett


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Fri 13, 2012 7:53 am 
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Joined: Feb Thu 24, 2011 1:29 am
Posts: 3021
Location: Dallas, TX - in the city but with bobcats and coyotes
Yes, Brett did a killer write-up with visual teaching aids.
I never thanked you for that work, Brett. :oops:
Thank you :!:
BTW: The OP on that thread never posted again after 12/14 so one can only assume that his problem with the radio was solved. It just might have been a short on that third transistor.. :wink:

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In a triode, no one can hear you screen.


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Fri 13, 2012 8:15 am 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 2444
Location: Sunnyvale CA
mescalero wrote:
BTW: The OP on that thread never posted again after 12/14 so one can only assume that his problem with the radio was solved. It just might have been a short on that third transistor.. :wink:


Maybe. I sent him a PM around Christmas and he said he was going to go look for parts and get back to me/us later.
Brett


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sat 14, 2012 8:11 am 
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Joined: Jan Thu 12, 2012 11:03 pm
Posts: 9
mescalero wrote:
Service data here:
http://www.transoceanic.nostalgiaair.org/pics/r3000sm.pdf

Expected voltages for the seven test points are listed in the service manual.

It is also possible that the electrolytic filter caps failed when reverse biased. However, getting audio is a sign that they may well be OK.
Do both AM and FM fail? If so, there is a section in common to both modes that would be suspect.

Yes. Both AM and FM fail. Me and my dad just got the chassis out. What's the best way to test the filter capacitors? :?: Also, thanks for the help!


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sat 14, 2012 9:04 am 
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Joined: Jan Thu 12, 2012 11:03 pm
Posts: 9
Brett_Buck wrote:
mescalero wrote:
Service data here:
http://www.transoceanic.nostalgiaair.org/pics/r3000sm.pdf

Expected voltages for the seven test points are listed in the service manual.

It is also possible that the electrolytic filter caps failed when reverse biased. However, getting audio is a sign that they may well be OK.
Do both AM and FM fail? If so, there is a section in common to both modes that would be suspect.


I did something similar but mine "recovered" after a few hours of just sitting - presumably because I didn't quite kill the backwards-voltaged capacitors.

I would strongly suspect the electrolytic caps across the power supply. They're easy to get to, and the two likely candidates are right under the opening in the chassis where the speaker goes through. And definitely check the voltages on FM and AM.

The part numbers are in the service manual but if you check this post:

http://antiqueradios.com/forums/viewtop ... royal+3000

you will find some of the variations, and some of the NTE equivalent part numbers. It also has the corrected voltages (there's an error in the service manual). If it's just AM/SW that has the problem you can use the data in that post to troubleshoot, as well. If it's both FM or AM, I doubt that it's the oscillator (since it would be two separate oscillators), it would almost have to be the IF transistors or maybe the first AF (check the schematic and see if the external audio is tapped before or after the first AF stage).

I have made many various "oopsies" with 60-s style bipolar transistors over the years and I would be a little surprised of 12v the wrong way actually blew any of them, but it's possible.

Brett

All bands are dead. We couldn't find the audio out on the schematic, but looking at the chassis, it appears to be connected to the first af transistor. When we ran audio into the output jack, we had decent volume, but it wasn't 100%. Also, after the test, the audio transformer was fairly hot. Here's the test point voltages again, they were a little jumbled on my first post:
FM AM
1:-0.61 1:-0.61
2:-0.51 2: 0
3:-0.51 3:-.36
4: 0 4: 0
5:-0.20 5:-5.40
6:-0.20 6:-3.89
7:-0.28 7:-3.89
Thanks for all the help!


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sat 14, 2012 8:01 pm 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 2444
Location: Sunnyvale CA
dodge2461 wrote:
All bands are dead. We couldn't find the audio out on the schematic, but looking at the chassis, it appears to be connected to the first af transistor. When we ran audio into the output jack, we had decent volume, but it wasn't 100%. Also, after the test, the audio transformer was fairly hot. Here's the test point voltages again, they were a little jumbled on my first post:
FM AM
1:-0.61 1:-0.61
2:-0.51 2: 0
3:-0.51 3:-.36
4: 0 4: 0
5:-0.20 5:-5.40
6:-0.20 6:-3.89
7:-0.28 7:-3.89
Thanks for all the help!


Those are clearly not right and the transformer should definitely not be getting hot. I wouldn't bother with testing the electrolytic capacitors, just replace them. I would strongly suspect C61 (500 mfd, big one on the front right below the speaker opening ) and C62 (50 mfd, just to the left of C61 as you look at it). Note that the radio is POSITIVE ground, so hook the positive side up to the chassis.

You mentioned swapping the transistors around with another radio - could you maybe explain that some more?

I think the 1st Audio is not involved in getting audio into the driver and output transistors, by the way, looks like it picks off the output to send out. The "input" mode it puts it into the tone/volume control and then drives the driver.

Brett


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sun 15, 2012 1:46 am 
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Joined: Jan Thu 12, 2012 11:03 pm
Posts: 9
Brett_Buck wrote:
dodge2461 wrote:
All bands are dead. We couldn't find the audio out on the schematic, but looking at the chassis, it appears to be connected to the first af transistor. When we ran audio into the output jack, we had decent volume, but it wasn't 100%. Also, after the test, the audio transformer was fairly hot. Here's the test point voltages again, they were a little jumbled on my first post:
FM AM
1:-0.61 1:-0.61
2:-0.51 2: 0
3:-0.51 3:-.36
4: 0 4: 0
5:-0.20 5:-5.40
6:-0.20 6:-3.89
7:-0.28 7:-3.89
Thanks for all the help!


Those are clearly not right and the transformer should definitely not be getting hot. I wouldn't bother with testing the electrolytic capacitors, just replace them. I would strongly suspect C61 (500 mfd, big one on the front right below the speaker opening ) and C62 (50 mfd, just to the left of C61 as you look at it). Note that the radio is POSITIVE ground, so hook the positive side up to the chassis.

You mentioned swapping the transistors around with another radio - could you maybe explain that some more?

I think the 1st Audio is not involved in getting audio into the driver and output transistors, by the way, looks like it picks off the output to send out. The "input" mode it puts it into the tone/volume control and then drives the driver.

Brett

On the transistor swap- The dead radio is chassis 12kt40z8. We also have a chassis 12kt40z3(This is the radio we swapped transistors with, it works fine). All of the transistors except for the Fm section had different part numbers. We were kind of hesitant, but we decided to briefly swap transistors one stage at a time. The oscillator transistor had different number of pins,so we could not swap that one stage. None of the transistors from the good radio made any change in the bad radio. All of the transistors from the bad radio worked in the good radio. The audio amp transistors did work, but were somewhat distorted and were hot when we put them back in the dead radio. The audio amp transistors in the good radio are larger than the ones in the dead radio.

Thanks for helping! i'm excited to get it working! :lol:


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sun 15, 2012 2:51 am 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 2444
Location: Sunnyvale CA
dodge2461 wrote:
On the transistor swap- The dead radio is chassis 12kt40z8. We also have a chassis 12kt40z3(This is the radio we swapped transistors with, it works fine). All of the transistors except for the Fm section had different part numbers. We were kind of hesitant, but we decided to briefly swap transistors one stage at a time. The oscillator transistor had different number of pins,so we could not swap that one stage. None of the transistors from the good radio made any change in the bad radio. All of the transistors from the bad radio worked in the good radio. The audio amp transistors did work, but were somewhat distorted and were hot when we put them back in the dead radio. The audio amp transistors in the good radio are larger than the ones in the dead radio.


OK, so all the transistors from the broken radio worked in the good radio, and when you put the transistors from the good radio into the bad one, it still didn't play. That essentially exonerates the transistors.

As an aside, the "3-legged" transistor is probably a replacement. The original oscillator transistor had 4 pins in line. The pin in the middle, adjacent to the gap, is just hooked up to the case of the transistor and doesn't necessarily need to be there. The 3-legged replacement probably just doesn't have that one, so you could use it. I would bet a fair bit of money that if you look at the socket in the good radio (where the 3-legged transistor came from), you will find 4 pins holes, and the 3 legs go into the two outside pins and the middle pin and leaved the shield hole open. It makes more sense looking at the pictures in the other thread. So you could substitute that one, too. But I don't think it matters, that's not likely the problem.

I will also make an additional guess - that the lettering on the 3-leg transistor says "NTE 160" on it!

I stick with the original idea - that C61 and/or C62 are bad (show low equivalent resistance) and is shunting off most of your B+ voltage, and probably you are getting DC through the output transformer (which is why it is getting hot). the low B+ voltage is probably preventing oscillation, but it's good enough to make the output transistors work, weakly.

I THINK you can simply disconnect C61 and C62 and test it - VERY BRIEFLY - to see. I would recommend any extended run time, if you are getting high currents through the transformer or transistors, you are likely to fry something eventually. It might be a little noisy with them disconnected but your voltages should be OK.

If it was me, I would just cut those babies out of there, replace them and then try again. These are the parts most likely to be damaged by reverse polarity and they are hooked directly across the power supply. But I have the parts available. I don't know if you can get them locally - maybe Rat Shack? The values aren't critical, so anything withing a country mile of the 50 or 500 is good enough to test, just make sure they are 12 V rated or more, or you could wind up with 20 seconds of playing, then the same problem, and some confetti to clean up.

Brett


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sun 15, 2012 3:35 am 
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Joined: Jan Thu 12, 2012 11:03 pm
Posts: 9
Brett_Buck wrote:
dodge2461 wrote:
On the transistor swap- The dead radio is chassis 12kt40z8. We also have a chassis 12kt40z3(This is the radio we swapped transistors with, it works fine). All of the transistors except for the Fm section had different part numbers. We were kind of hesitant, but we decided to briefly swap transistors one stage at a time. The oscillator transistor had different number of pins,so we could not swap that one stage. None of the transistors from the good radio made any change in the bad radio. All of the transistors from the bad radio worked in the good radio. The audio amp transistors did work, but were somewhat distorted and were hot when we put them back in the dead radio. The audio amp transistors in the good radio are larger than the ones in the dead radio.


OK, so all the transistors from the broken radio worked in the good radio, and when you put the transistors from the good radio into the bad one, it still didn't play. That essentially exonerates the transistors.

As an aside, the "3-legged" transistor is probably a replacement. The original oscillator transistor had 4 pins in line. The pin in the middle, adjacent to the gap, is just hooked up to the case of the transistor and doesn't necessarily need to be there. The 3-legged replacement probably just doesn't have that one, so you could use it. I would bet a fair bit of money that if you look at the socket in the good radio (where the 3-legged transistor came from), you will find 4 pins holes, and the 3 legs go into the two outside pins and the middle pin and leaved the shield hole open. It makes more sense looking at the pictures in the other thread. So you could substitute that one, too. But I don't think it matters, that's not likely the problem.

I will also make an additional guess - that the lettering on the 3-leg transistor says "NTE 160" on it!

I stick with the original idea - that C61 and/or C62 are bad (show low equivalent resistance) and is shunting off most of your B+ voltage, and probably you are getting DC through the output transformer (which is why it is getting hot). the low B+ voltage is probably preventing oscillation, but it's good enough to make the output transistors work, weakly.

I THINK you can simply disconnect C61 and C62 and test it - VERY BRIEFLY - to see. I would recommend any extended run time, if you are getting high currents through the transformer or transistors, you are likely to fry something eventually. It might be a little noisy with them disconnected but your voltages should be OK.

If it was me, I would just cut those babies out of there, replace them and then try again. These are the parts most likely to be damaged by reverse polarity and they are hooked directly across the power supply. But I have the parts available. I don't know if you can get them locally - maybe Rat Shack? The values aren't critical, so anything withing a country mile of the 50 or 500 is good enough to test, just make sure they are 12 V rated or more, or you could wind up with 20 seconds of playing, then the same problem, and some confetti to clean up.

Brett

We just got back from "Rat Shack" :wink: , and got some capacitors. We found a 47uF and a 470 uF,both at 35 WVDC. Our only concern is that these replacements are so much smaller than the originals. Are these OK to use or are we missing something? By the way, the transistor number is 121-48, which matches the number in the radio, however it does go in a 4-pin socket. There's also VFA2745E on the transistor.

VERY excited and hoping to have it up and running tonight :D


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sun 15, 2012 3:43 am 
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Location: Indianapolis, IN
You're fine with those caps---electrolytics have decreased a lot in physical size through the years thanks to improving technology...

John


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sun 15, 2012 4:11 am 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 2444
Location: Sunnyvale CA
dodge2461 wrote:
We just got back from "Rat Shack" :wink: , and got some capacitors. We found a 47uF and a 470 uF,both at 35 WVDC. Our only concern is that these replacements are so much smaller than the originals. Are these OK to use or are we missing something? By the way, the transistor number is 121-48, which matches the number in the radio, however it does go in a 4-pin socket. There's also VFA2745E on the transistor.

VERY excited and hoping to have it up and running tonight :D


Those are fine, and should have a little margin on the voltage. The originals were only rated for 12v and they saw up to 12.5 with new batteries. They're a lot smaller just because technology to make them has advanced considerably in the last 50 years.

I sure hope this is the problem, if it isn't, it might be pretty tough to diagnose over the internet. You would want to replace them in any case, since they were subject to reverse polarity and overstressed.

A 121-48 should work in the oscillator position, but it must be a later replacement (or someone cut the shield pin off, which sometimes makes them work). It was working before, right?

Brett


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sun 15, 2012 4:53 am 
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Joined: Jan Thu 12, 2012 11:03 pm
Posts: 9
Brett_Buck wrote:
dodge2461 wrote:
We just got back from "Rat Shack" :wink: , and got some capacitors. We found a 47uF and a 470 uF,both at 35 WVDC. Our only concern is that these replacements are so much smaller than the originals. Are these OK to use or are we missing something? By the way, the transistor number is 121-48, which matches the number in the radio, however it does go in a 4-pin socket. There's also VFA2745E on the transistor.

VERY excited and hoping to have it up and running tonight :D


Those are fine, and should have a little margin on the voltage. The originals were only rated for 12v and they saw up to 12.5 with new batteries. They're a lot smaller just because technology to make them has advanced considerably in the last 50 years.

I sure hope this is the problem, if it isn't, it might be pretty tough to diagnose over the internet. You would want to replace them in any case, since they were subject to reverse polarity and overstressed.

A 121-48 should work in the oscillator position, but it must be a later replacement (or someone cut the shield pin off, which sometimes makes them work). It was working before, right?

Brett

We replaced the capacitors, but the radio is still dead :cry: We only had the Wavemagnent connected, but didn't get anything. We connected another speaker(not the one in the case) and got no sound :cry: we took the test voltages again, and here's as follows:
FM:
1:-.87
2:-.72
3:-.72
4:0
5:-.29
6:-.31
7:-.40
AM
1:-.88
2:-.67
3:-.65
4:0
5:-7.59
6:-5.62
7:-5.47

Any ideas, or is this a parts radio?
ALSO: when my dad turned it off, he said the audio transformer was noticeably warm :x


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sun 15, 2012 6:19 am 
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Posts: 2444
Location: Sunnyvale CA
dodge2461 wrote:
Any ideas, or is this a parts radio?
ALSO: when my dad turned it off, he said the audio transformer was noticeably warm :x



Oh, don't give up on it! I note that the new caps made a big difference in the voltages, but something is still way off. Let me think about it some more, and I am sure that others will add their inputs, too.

It seems as if you are getting DC through the output transformer. You did substitute both output transistors with known good ones, right?

Brett


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sun 15, 2012 7:28 am 
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Brett_Buck wrote:
dodge2461 wrote:
Any ideas, or is this a parts radio?
ALSO: when my dad turned it off, he said the audio transformer was noticeably warm :x



Oh, don't give up on it! I note that the new caps made a big difference in the voltages, but something is still way off. Let me think about it some more, and I am sure that others will add their inputs, too.

It seems as if you are getting DC through the output transformer. You did substitute both output transistors with known good ones, right?

Brett

We did try other transistors, maybe we should try turning it on without any output transistors and see if it still gets warm. The test voltages are getting better so at least we're making progress. I just hope we didn't fry to many parts, or else it might be to hard to fix. We keep looking at the schematic and it makes a little more sense each time.

I appreciate the help!


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Sun 15, 2012 8:26 am 
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dodge2461 wrote:
We did try other transistors, maybe we should try turning it on without any output transistors and see if it still gets warm. The test voltages are getting better so at least we're making progress. I just hope we didn't fry to many parts, or else it might be to hard to fix. We keep looking at the schematic and it makes a little more sense each time.

I appreciate the help!


My gut feeling would be to replace most of the other electrolytic caps, particularly those around the audio end of the chain, near the volume control. But I can't see how that causes abnormal current through the output.

I would also check the voltages at the collectors of the output transistors to see of one or the other is conducting or short and that the output transformer is intact. -12 volts is supplied the center tap of the output transformer and in the absence of a signal that should to through both sides of the primary and appear at the collectors. If one or the other transistor is "on" with no signal it would put DC through the windings, heating it up and maybe sagging a lot of the other voltages. If you test it with the output transistors out that would certainly not cause the transformer to heat up, both ends of the transformer would be open and then there should be 12V.

Brett


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Mon 16, 2012 8:47 am 
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Brett_Buck wrote:
dodge2461 wrote:
We did try other transistors, maybe we should try turning it on without any output transistors and see if it still gets warm. The test voltages are getting better so at least we're making progress. I just hope we didn't fry to many parts, or else it might be to hard to fix. We keep looking at the schematic and it makes a little more sense each time.

I appreciate the help!


My gut feeling would be to replace most of the other electrolytic caps, particularly those around the audio end of the chain, near the volume control. But I can't see how that causes abnormal current through the output.

I would also check the voltages at the collectors of the output transistors to see of one or the other is conducting or short and that the output transformer is intact. -12 volts is supplied the center tap of the output transformer and in the absence of a signal that should to through both sides of the primary and appear at the collectors. If one or the other transistor is "on" with no signal it would put DC through the windings, heating it up and maybe sagging a lot of the other voltages. If you test it with the output transistors out that would certainly not cause the transformer to heat up, both ends of the transformer would be open and then there should be 12V.

Brett

Today, we stared by turning on the radio and feeling to see if any of the caps were getting hot. I then felt a output transistor, and burnt my finger. We thought these transistors were only getting hot in the good radio due to there smaller size and incorrect number. We never checked them for overheating in the dead radio, until tonight when we touched it :oops: . The voltages at the collector are -9.3 and -5.2. One transistor is shorted b-e and the other transistor is shorted b-e and b-c. We'll order some replacements but expect there's more wrong than just the transistors since swapping with the good radio didn't change anything. We'll probably change some caps in that circuit before installing the new transistors.

Let me know if you have any suggestion and thanks for the help.


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Mon 16, 2012 9:03 am 
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Posts: 2444
Location: Sunnyvale CA
dodge2461 wrote:
Brett_Buck wrote:
dodge2461 wrote:
We did try other transistors, maybe we should try turning it on without any output transistors and see if it still gets warm. The test voltages are getting better so at least we're making progress. I just hope we didn't fry to many parts, or else it might be to hard to fix. We keep looking at the schematic and it makes a little more sense each time.

I appreciate the help!


My gut feeling would be to replace most of the other electrolytic caps, particularly those around the audio end of the chain, near the volume control. But I can't see how that causes abnormal current through the output.

I would also check the voltages at the collectors of the output transistors to see of one or the other is conducting or short and that the output transformer is intact. -12 volts is supplied the center tap of the output transformer and in the absence of a signal that should to through both sides of the primary and appear at the collectors. If one or the other transistor is "on" with no signal it would put DC through the windings, heating it up and maybe sagging a lot of the other voltages. If you test it with the output transistors out that would certainly not cause the transformer to heat up, both ends of the transformer would be open and then there should be 12V.

Brett

Today, we stared by turning on the radio and feeling to see if any of the caps were getting hot. I then felt a output transistor, and burnt my finger. We thought these transistors were only getting hot in the good radio due to there smaller size and incorrect number. We never checked them for overheating in the dead radio, until tonight when we touched it :oops: . The voltages at the collector are -9.3 and -5.2. One transistor is shorted b-e and the other transistor is shorted b-e and b-c. We'll order some replacements but expect there's more wrong than just the transistors since swapping with the good radio didn't change anything. We'll probably change some caps in that circuit before installing the new transistors.

Let me know if you have any suggestion and thanks for the help.


Sounds like a plan forward. Burned your finger, eh? Not a good sign!

Brett


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 Post subject: Re: Zenith Trans-Oceanic 3000-1 Not Working
PostPosted: Jan Tue 24, 2012 1:51 am 
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Posts: 647
Location: Cedartown,Ga. USA
I had that same problem in mine, the outputs would burn you. When I finally got all the correct transistors in place ,she went to working! Don't give up. I think it's probably a transistor problem.
Rickey


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