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46-480 Recapped now nothing.....
#1
Hi all,

I recently recapped a 46-480 that was working, albeit poorly. Now I have nothing when the tuner or band switches are moved.

The Tone control does seem to get a response from the speaker, but that's it.

I've retraced my steps and barring brain fade, I think I recapped correctly.

In the next week or so, I'll be trying to sort this out. I was wondering if any members could point me to anything specific I should be looking for while diagnosing this chassis?

Thanks!
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#2
When recapping, you could move wires. See if you did.
Also if you disturbed any RF transformer pins, you could pitentially break the magnet wire.
Check conductivity.

And, when soldering around old carbon resistors, if you did not replace those, you could push some of them fully out of tolerance.
Recheck the resistors.

And tube panels, of course. Try rock tubes, see if anything happen.
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#3
Here's the schematics for reference:

http://www.nostalgiaair.org/PagesByModel...013602.pdf

If your tone control (which I believe is R27) makes some noise on your speaker (meaning a little scratching, but otherwise silent), you may conclude that your speaker, audio output transformer, and 2nd AF amplifier are probably OK.

What happens next depends on what test equipment you have on hand.

Ideally you could trace signals with an O-Scope from tube to tube (output from plate of tube X to input grid of tube Y, etc.) When you lose signal, work your way back to where it was last good.

If you have a signal generator with an audio output, there is a test point under the chassis near the back labeled "AF Test" where you might be able to inject an audio signal to check the rest of the audio section. That will eliminate everything after that point, including the first audio amp and volume pot.

If all you have is a multimeter, you can check connections from component to component and resistors without parallel circuits, but Easter-egging like that wastes a lot of time.
It's not how bad you mess up, it's how well you can recover.
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#4
Hi and welcome to the Phorum!
I would just double check my work making sure that all of the replacement caps are where they should be. After that I would do the previous mentioned things to see if I could find a signal and trace it till it ends and find out why.
GL de N3GTE
Terry
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#5
Hi Lawrence, and welcome!
I know this has been mentioned many times, but when recapping, one or two should be done at one time, then a quick test done. Starting with the filers first. We have seen many radios that were somewhat working, turn into a non working set. By replacing one or two at a time, you will instantly know where to look when something does not work. Bad part (rare) or a miswiring mistake.
Eric has good advice to get the troubleshooting started, and hope you can find the (usually simple) mistake you may have made. Let us know what you find.
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#6
The problem is most likely something you did in your rework. Some common issues in no particular order:
-> New component soldered to the wrong place.
-> New component has the wrong value, for instance replacing a 10,000 ohm resistor with a 100,000 ohm resistor.
-> Solder blob that is shorting out two terminals that shouldn't be connected.
-> Electrolytic cap wired in reverse.
-> Bad (cold) solder joint on one of your solder connections.

Good luck.
Jon
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#7
Welcome!

+1 on the double check your recapping job. I just discovered an incorrect solder point on my own recap job that caused problems with operation. I took pictures and made notes as it came apart. I discovered that my disassembly notes were incorrect, thus I reassembled it incorrectly... Doh! After careful checking, it now works.

Eric
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#8
Yes, same thing here at work when repairing ATM's.. If something worked before you touched it then it is a very good chance you did something. Best to check all your work.
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#9
It is VERY easy to misconnect something. I did it on my 48-482 rebuild... one cap soldered to a terminal one off from where it should have been... and I spent DAYS sorting it out until I found my mistake. Best of luck. It can happen to the best of us.
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