Using A Signal Tracer To Identify Distortion + Prototype Chassis Stand
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- Опубликовано: 3 ноя 2017
- Checking out a friend's Philco 47-205 that suffers from severe distortion. I'm using my Heathkit IT-12 Signal Tracer to identify the issue before taking steps to correct the problem. You'll never guess what caused this one...
A sneak peak at a prototype chassis stand for those small All American Five radios. Detailed plans are forthcoming in a future video.
Thanks for watching and subscribing to my channel on vintage radio repair. 
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I have radios to re-cap (and troubleshoot when necessary) and am reviewing as many videos as I can to get tips on how to proceed. This video is perfect and I now want to add a signal tracer to my bench. Thank you for a great how-to on steps to take to help find the gremlins. I would never have guessed an antenna lead break to manifest itself as distortion. But, I am a newby. I will be watching for other videos you have posted. Thanks again!
VERY helpful Don! I have a Crosley Dashboard that has been giving me fits for a long while now. You've given me a great blueprint to follow to try trace the issue. Thx Mike
+Michael McKenzie Glad it helped Mike. When you get it going, reach out and let me know what the root cause was if you don’t mind. Best, Don
Don,
I really enjoyed this video. Watching how you traced down the fault, using the schematic itself as part of the diagnostic process was very helpful. It will help me immensely when I run into a problem like this.
Best regards, Tom
+THOMMGB Thank you Tom. It was rewarding to get the root cause. Sometimes as you know many hours can be spent looking for the needle in the haystack. Best, Don
Excellent demo on trouble shooting, thanks
+Mike Thuman Mike, I appreciate it. It was an odd issue and the audio distortion itself was different from the norm. Thanks again for your feedback and taking time to watch. Best, Don
don you do such great work and the video's are easy to follow along
+bobby burress Bob, I appreciate and value your feedback. Thank you again. Best, Don
Had this on a Zenith, customer brought it in for repair without the back cover and antenna. Fixed the FM then Spent the time on the AM then figured that the bias to the grid of the RF amp goes through the antenna coil. AGC won’t work and signal over amplifies. Did not have proper voltage on the grid.
Glad to hear you isolated the issue. Thanks for watching. Best, Don
WOW! ...... I was waiting for you to find that the B+ cap was wired wrong.... Thanks!
+Carl Burgess To your point Carl, it sounded like a B+ issue. That was my first thought as well. Thank you for viewing. Best, Don
Great troubleshooting video Don! Good example of using a signal tracer and what to expect. I really thought you would find the distortion around those IF's or a bad cap(even tho they were new, maybe overheated or just a bad one). It was surprising and good info to keep in the vault in the future. Thanks for sharing this! The restore looks like a good job, tell ur friend he did good! Not sure what the dust bunnies were, maybe cotton from cleaning, but ai kept seeing ghosts in the chassis! Lol great job! Best--Larry
+Backtothefutureradios Larry, the antenna was not on my mind. It sounded like AC hum. The old radio was in his shed. I should have taken some time to blow out the dust bunnies (ghost) and bugs. Lol Best, Don
Vin, thank you. The volume control has to be turned up on the radio to test the audio on the plate and grid of the power output tube. The same holds true for wiper (center position) of the volume control. All RF test points the volume can be muted. You may of seen me turning the volume up and down while probing in the RF section. This was done to understand if the radio was being de-tuned by touching the probe to the circuit under test. Hope this answers your question and thanks again for reaching out. Best, Don
Great troubleshooting!
+The Radio Shop Buddy, thank you. It was an odd issue for sure and not one that my ears connected with the root cause. Best, Don
Great video... Thanks
+bbugin4u Thank you, much appreciated. Best, Don
Good trouble shooting big thumbs up mate
+allan mitchell Thank you Allan. It was an odd issue and not expected for sure. Best, Don
Don,
I have to admit that I thought you were a little crazy when you started looking at the antenna. I have never seen a antenna cause such bad distortion - weak signal, or intermittent reception yes but not distortion. Well I guess the old saying that once you've exhausted checking all the good parts, whatever you have left must be the problem! LOL
Great job! I always pick up a few tips from your videos!
+Jim Kodysz Thank you Jim. I was very surprised to find the issue to be a defective loop antenna. I learned something new myself. Thank you for watching and your feedback. Best, Don
Don, I would not have guessed that an open antenna coil would cause distortion.
Am I correct with this?-
The antenna forms a tuned circuit with the tuning capacitor's antenna section, unlike a radio that merely has an antenna connection. Therefore, a break in the antenna does not just cause a weak signal, but actually disrupts the first tuned stage in the radio. Is that your assessment?
I am about to attempt to restore an AA5 bakelite Arkay brand set. The case is perfect, but it was a kit and it looks like it was assembled at gunpoint. Anyway, one of the coil antenna leads is broken and I would never have suspected that was the cause of it not working when I first fired it up. So thanks for the video, it saved me much time and frustration.
thx !
You are welcome. Thanks for watching. Best, Don
So where was the buzz coming from.......... and why dont other similar sets do this when the antenna is disconnected ?
What is the green clip connected to on the other end?
From the circuit common ground back to the signal tracer ground. Best, Don
@RestoreOldRadios thank you for the response, Don. ReSon I was asking is because I'm restoring an IT-12 right now. I just replaced the filter can with a custom made one, and was going to put a bnc connector on it. I noticed your ground wire is not on the probe, did you run it out the back? I'm pretty new to all this and thank you for your willingness to tech us!
Why would he change all the caps but two of them,maybe because they were hard to reach ,but caps that old aren't relieable.,I shot gun all the caps ,then if there a problem if most likely else where. But catching that antenna problem ,I no I would have not caught that one gives me something else to check thanks
Hey Ron - I was guiding and supporting my friend through the repair process. Not having the parts on hand was the limiting factor. The open loop antenna was interesting to find. Best,, Don
You have hum from ps. Scope is infinitely better, thanks
Or have Heater to cathode leak
How bout that, hum induced in bad coil
Something does not add up here at all. This is not an antenna issue. I don't know what you fixed, but I seriously doubt the antennae was the issue unless it was shorted directly to ground, still........hmmmm
That is what I thought. Weak signal yes, but why was it distorted?
That is what I thought. Weak signal yes, but why was it distorted?