Zenith 10S464

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Zenith 10S464

Post by tsisko on Fri Jan 04, 2013 11:35 pm

Hello All,

I had a 10S464 working and I was going to hard wire a ipod jack under the chassis. I pulled the old girl out of the cabinet and the 10ohm wire wound was dangling by a hair. It was black and almost burned through. All the caps were original so I replaced the caps and the resistor. Brought it back up and now I have a screech on half the bandwidth. Could it have been serviced and tuned with the old bad/leaky caps and now the new are bringing it out of alinement? What is the first step?
Should I try to adjust the alinement and see if the screech will go away? O' all tubes are good.
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Re: Zenith 10S464

Post by N7ZAL on Sat Jan 05, 2013 5:21 pm

Can you describe the "screech" better? Is it an oscillation of a fixed frequency?
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Re: Zenith 10S464

Post by Dr. Radio on Sat Jan 05, 2013 7:27 pm

tsisko wrote:Hello All,

I had a 10S464 working and I was going to hard wire a ipod jack under the chassis. I pulled the old girl out of the cabinet and the 10ohm wire wound was dangling by a hair. It was black and almost burned through. All the caps were original so I replaced the caps and the resistor. Brought it back up and now I have a screech on half the bandwidth. Could it have been serviced and tuned with the old bad/leaky caps and now the new are bringing it out of alinement? What is the first step?
Should I try to adjust the alinement and see if the screech will go away? O' all tubes are good.

I checked the schematic: http://www.nostalgiaair.org/PagesByModel/689/M0024689.pdf

I'm a bit confused...There is a input jack on this radio already, there's no need to hard-wire anything. It's labeled "television/radio" but all it is, is a two-pin connector that will accept any audio.

Were you using the radio as-is with original capacitors before you decided to pull it apart? That's awfully risky/dangerous, but I guess at this point, it's all water under the bridge as they say.

The 10 ohm wirewound would burn-up if C20 was leaky or shorted. You may need to go thru this radio step by step if you were using it as-is, as it may have been on the verge of self-destruction.

What tools/experience do you have for troubleshooting/repair?

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Re: Zenith 10S464

Post by tsisko on Sun Jan 06, 2013 10:51 pm

It is oscillation. The reason I was going to hard wire it is because one of the input pins was split and broke. Someone inserted something too large into the input. It was working, but like I said there was a resistor about to fry. It was black and going to fall apart.
I replaced the caps like I have on other radios. All were original Zenith caps. Most were bulging and sweating so I replaced most of them. I did replace C20. Half the dial will bring in stations but the other half will give me the noise. I have a basic knowledge with antique radio repair but I have a neighbor that gave me a tube tester, signal generator, and signal tracer. I do have good knowledge of modern electronics. My neighbor's brother in law is an engineer and has been into tube radios for years. He told me he has run into this many times before...and said it could be a few things...a cap and also mentioned that someone servicing/tuned the radio before with bad caps. He said I could start with seeing if I move the tuning screws and see if it gets rid of the oscillation. Thoughts?
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Re: Zenith 10S464

Post by Resistance is Futile on Mon Jan 07, 2013 7:06 am

Realign the radio as there can be many problems. Voltages need to be checked and tuning cap also for shorts.
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Re: Zenith 10S464

Post by N7ZAL on Mon Jan 07, 2013 9:21 pm

Realign the radio as there can be many problems.

Have to agree with Cliff, and during the alignment procedure it could point you to the stage that is giving you a problem.
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Re: Zenith 10S464

Post by Wildcat445 on Mon Jan 07, 2013 9:38 pm

How can an accurate alignment be done if there is a possible problem elsewhere in the radio? Unless I am missing something, this procedure would be putting the cart before the horse. Alignment will not fix bad caps or other electrical troubles.

If Cliff is referring to using a signal generator as a diagnostic tool, that would certainly be worth a shot.

A disciplined diagnostic procedure is the only way to find and repair any fault. Shotgunning the diagnostics and throwing parts at it may not result in a successful outcome.

Regards

WC


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Re: Zenith 10S464

Post by N7ZAL on Mon Jan 07, 2013 9:45 pm

I would think if you start at the front end, inject a signal, and walk your way through the different stages it might help.
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Re: Zenith 10S464

Post by tsisko on Tue Jan 08, 2013 7:10 pm

Mr. Repairtech,
Thank you for your post. I was simply asking for some member's feedback in determining a root cause.
I was trying to gather info and see if anyone has run into the same issue. That info would then help me diagnose and move forward. This is an area where members should feel free to ask questions. Asking should be encouraged in this forum. We can not all be THE Repairtech!

All others, thank you for your insight. I will start with checking/testing the new caps. Like I mentioned, all was working fine until I replaced the caps and resistor. After I clear the caps I will then move from there.

Thank you all again!


Last edited by Resistance is Futile on Tue Jan 08, 2013 9:23 pm; edited 1 time in total (Reason for editing : Moderators modifying discussion to keep on track)
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Re: Zenith 10S464

Post by tsisko on Tue Jan 08, 2013 8:33 pm

THAT! LOL!
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Re: Zenith 10S464

Post by sprman on Wed Jan 09, 2013 7:19 pm

Shoot take your time and start from the ant stage and go stage by stage.Check everything caps, resistors all of them.Check the tubes to and do resistance voltage checks.Sprman

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Re: Zenith 10S464

Post by Resistance is Futile on Wed Jan 09, 2013 9:56 pm

Idea Using these methods you can avoid a lot of willy-nilly guessing.

Make yourself a check list to keep your troubleshooting in order.

1a. Get the schematic.

1b. Set up your test equipment and tools

1c. You have made a visual check for damaged and destroyed components.

2. Check all wires and connections for broken or cold solder joints.
and Trace out each wire for proper connections.

4. Make a list of the tube numbers on your chart in a descending column with spaces for listing pin numbers, Also mark those tube numbers on the chassis next to each tube socket.

5. Then post the measured voltages of tube pin numbers and

6. Check the voltages of other parts.

7. test the tubes You have already have

8. Troubleshoot by stage, using process of elimination.

9. Record each step so you know where you left off.

10. Once you get things operating then you can focus on doing the alignment.

You can bypass some steps as you get aquanted with troubleshooting and it becomes natural.
( I think this is worth posting on my forum too! study What a Face Idea )


Last edited by Resistance is Futile on Wed Jan 09, 2013 10:13 pm; edited 1 time in total
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Re: Zenith 10S464

Post by tsisko on Thu Jan 10, 2013 12:01 pm

Thank you very much Ken. I'm in the process checking the caps...I have a hairy feeling you're right.
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Re: Zenith 10S464

Post by Guest on Thu Jan 10, 2013 6:46 pm

Resistance is Futile wrote: Idea Using these methods you can avoid a lot of willy-nilly guessing.

Make yourself a check list to keep your troubleshooting in order.

1a. Get the schematic.

1b. Set up your test equipment and tools

1c. You have made a visual check for damaged and destroyed components.

2. Check all wires and connections for broken or cold solder joints.
and Trace out each wire for proper connections.

4. Make a list of the tube numbers on your chart in a descending column with spaces for listing pin numbers, Also mark those tube numbers on the chassis next to each tube socket.

5. Then post the measured voltages of tube pin numbers and

6. Check the voltages of other parts.

7. test the tubes You have already have

8. Troubleshoot by stage, using process of elimination.

9. Record each step so you know where you left off.

10. Once you get things operating then you can focus on doing the alignment.

You can bypass some steps as you get aquanted with troubleshooting and it becomes natural.
( I think this is worth posting on my forum too! study What a Face Idea )

That should be stickied.

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Re: Zenith 10S464

Post by N7ZAL on Thu Jan 10, 2013 7:28 pm

Yes, I agree and that is a nice check list.
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Re: Zenith 10S464

Post by sprman on Fri Jan 11, 2013 7:16 am

Yes that should be stickied a darn good check list to use.Sprman

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Re: Zenith 10S464

Post by Resistance is Futile on Fri Jan 11, 2013 4:56 pm

It was posted as a helpful Hint and locked at the top of this forum Topic study
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Re: Zenith 10S464

Post by Ken g on Fri Jan 11, 2013 9:34 pm

It happens . I have done hundreds of radios . I usually order caps in bulk , the yellow ones ... I was doing a chassis and did my usuall plug in after 3 caps and it didnt work . It was a defective shorted cap . That only happened once . I have cought some pretty difficult to find mistakes i made .

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