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Car radio gets only static need help troubleshooting

rcnrcf

Nov 27, 2021
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I have a seventh generation Honda Civic EX (sedan). The radio gets only static - both AM & FM. The CD player works just fine.

  1. The antenna is an in-glass antenna in the upper half of the rear window. The lower half of the window has more traces but they are mainly for defrosting ice/snow. But I "think" they also act as part of the antenna - I am not sure about the details. There is a connector for the upper traces (antenna) and there is one connector on both the sides of the lower traces (defroster). So three connectors total.
  2. I checked the antenna continuity all the way from the antenna plug to the connector on the in-glass antenna on the rear window and it is fine. Also, there is no short between the antenna ground and hot (not sure if I am using the correct terminology but I am referring to the tip of the plug as hot and the outer shell as the ground).
  3. Once I plug in the antenna in the back of the radio and check the continuity on the rear window between hot (upper connector in the rear window) and ground (one of the side connectors on the rear window) then I get continuity! Is it supposed to be this way?
  4. I get static even when I disconnect the antenna from the radio. I would imagine that I would get at least some reception, even though noisy! Has the tuner gone bad? Can I get some troubleshooting tips?
  5. I get static even when I connect an FM transmitter in the cigarette lighter i.e. I have a very strong source of FM signals. Again, has the tuner gone bad?
  6. I checked the grounding on the radio and that too is fine.
I can take apart the radio but I would not know which components to test as I do not even know what the problem is!

p.s. It is an old car and don't want to spend any money on it so I am taking the opportunity to mess with it and fix stuff and learn things at the same time. Thus, even though I can go buy a new radio - I do not want to, I would rather buy a new car! I am curious to know what the problem is and how to troubleshoot it all the way through, thus this post!
 

Bluejets

Oct 5, 2014
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Try another radio.
If it does the same that eliminates the radio.
One can get an elcheapo multi everything for around AUD$20 these days.
Even if a crappy buy, cheap tester.
 

rcnrcf

Nov 27, 2021
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Try another radio.
If it does the same that eliminates the radio.
One can get an elcheapo multi everything for around AUD$20 these days.
Even if a crappy buy, cheap tester.

I do not have another radio otherwise I would already tried it!
What does "elcheapo multi everything" mean, what type of device are you referring to?
 

davenn

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Sep 5, 2009
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  • I get static even when I disconnect the antenna from the radio. I would imagine that I would get at least some reception, even though noisy! Has the tuner gone bad? Can I get some troubleshooting tips?
  • I get static even when I connect an FM transmitter in the cigarette lighter i.e. I have a very strong source of FM signals. Again, has the tuner gone bad?
  • I checked the grounding on the radio and that too is fine.


you have only mentioned FM .... does it work on AM ?
 

rcnrcf

Nov 27, 2021
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you have only mentioned FM .... does it work on AM ?
I did mention that both AM & FM does not work. It's mentioned in the first line of the first post!
 
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Tha fios agaibh

Aug 11, 2014
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I can take apart the radio but I would not know which components to test as I do not even know what the problem is!
A radio model number would be a start.

Close up pictures of circuit board would be helpful.

And if you could post a schematic, well, that'd be phenomenal.

Be advised, a repair like this can be very labor intensive and often harder without the right test equipment.
 

73's de Edd

Aug 21, 2015
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Sir rcnrcf,
Lets not spend ANY of your hard earned "MUNNEYS" just yet, by initially testing out the antenna aspect of your radios troubleshooting.
For the last 80 years the most common connector has been the Coaxial Motorola auto antenna plug and jack.
My drawn illustration has the male connector and its A ground shell with its 3-4 tensioning bifurcations and the active antenna signal being carried in the center C-prime connection pin.
This male plug inserts into female B connector shell and bottoms out with male C-prime fully engaged into female C connector of the pair. (HEY . . .this is sounding NASTY **)
I chose a naked ** female connector, instead of an enclosed / hidden internals . . .one . . . so that you would be able to see how the top inserts RED circle triangular metal folds will surround and grip C-prime connector pin.
REFER TO THE BOTTOM PARTS NOW . . .
The plan now is to get about 10 ft of loose stranded hook up wire as is shown at D and then refer to female connector D-prime-prime to see that insulation is stripped and the then exposed wire ends are cut to about the length of C on the female connector (1/4 in) and all splayed back to about a 45 degree angles, equally spaced around, in a complete circle . . .as is shown in the illustration.
INSERTION . . . . .
Have the Motorola plug installed and then grip A and, in your gripping, place your thumbnail flush to E , , ,the face of the Motorola jack .and use that as a marker, (or USE a Sharpie marker) so that when you pull out the plug, you will then see how deep the connector is going inside B. AS well as where the C depth is .
So now you hold D prime prime wire up against the male connector and you can then see where to place a like fingernail grip on the wire to then insert it to have the clustered wire mass sprigs line up with the C female contact area..
If you have previously strung the hook up wire, vertically by using string / cord guying or being bound onto a thin vertical wood., etc pole .
Turning on the radio and tuning it in , should then have stations rolling in.
If you still have the same effect . . . . .HELLO INTERNAL RADIO PROBLEMS.
D-prime wire shown . . . .? . . . .was just another option, if you tried using just one 45 degree bend all of the wire strands en masse.
BUT then, you DO have to insert the bend so that it would NOT align into the wide open slot . . . since there's no contact . . . as is seen at the top of C

NOWGODOITTOIT !

upload_2021-12-12_5-41-54.png


73's de Edd . . . . .

What has four legs and an arm? . . . . . . . . . . one very- very happy pit bull.





 
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rcnrcf

Nov 27, 2021
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A radio model number would be a start.

Close up pictures of circuit board would be helpful.

And if you could post a schematic, well, that'd be phenomenal.

Be advised, a repair like this can be very labor intensive and often harder without the right test equipment.

I have attached the pictures of the part number label and PCB's top and bottom.

The part number is 39101-S5A-A610-M1 and I tried searching for the schematic on the internet but did not find any.

In the PCB pictures you will notice a component desoldered and kept beside. I am not sure what this component is, can you tell what it is? Quite a few different types of car radios have the same. Anyways, I took it out to see if it was the one causing the short between antenna socket's leads. But that is not the case as these socket leads are routed straight to the FM_ANT input to the part of the radio circuit that is in the Faraday Cage. That is, I am getting continuity between the antenna socket leads even after taking out that component. So maybe the short is in the circuit that is inside the Faraday Cage.

Q: I am guessing that there should not be any continuity between the antenna socket leads, however, is this assumption correct?

Q: Is the circuit inside the Faraday Cage the complete radio circuit or merely the demodulator, any ideas? I am planning to take it out and check to see if there is a short in that circuit. Hopefully only a component in there might have to be replaced.
 

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Tha fios agaibh

Aug 11, 2014
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Not unusual to have continuity or low resistance range from antenna to ground because there is often an inductor (coil of wire) parallel with the antenna.

That component on the side is a diode.
Where exactly did you desolder it? If it was in the signal path that may be your problem.
Inside the Faraday cage is the tuner section.

Careful, don't fiddle with any of its adjustments!

You can check that diode with the diode test function of a multimeter which should give a forward voltage reading in one direction.
 

rcnrcf

Nov 27, 2021
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I have marked the place from where the diode was taken out in the attached image. You can see that it was the first component connected to the antenna and was parallel to the same.

I'd measured the continuity of the diode both ways and got nothing. So that was one reason because of which I wasn't sure what component it is. And the second reason is the little knowledge I have about radios - that there is an inductor in parallel to the antenna. I know there are color coded inductors but I do not have any first hand experience to be sure if this component is an inductor or not!

Anyway, lets say this is a diode. Which type of diode is it, is it a schotky or a zener diode? What is its value?
Both ends look goldenish-orange and one end has a red band and the other has a green band.
If I know what it is and what its value is then I can order and install it and give it a try.
 

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Tha fios agaibh

Aug 11, 2014
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Which type of diode is it, is it a schotky or a zener diode? What is its value?
Both ends look goldenish-orange and one end has a red band and the other has a green band.
It looks like a germanium diode but couldn't tell you its value.
Looks to me like orange green red bands?
 

rcnrcf

Nov 27, 2021
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Yeah orange (both ends), green on one and red on the other end. I am unable to decode these color bands. A search on the internet shows me all different schemes!
 

Tha fios agaibh

Aug 11, 2014
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I have marked the place from where the diode was taken out in the attached image.
This picture baffles me because it looks like both sides of the diode appear to go to the same node.
In other words, there should be continuity between the two trace points.

Can you post a close up photo of this blue component?
Screenshot_20211215-042340_Chrome~2.jpg
 

rcnrcf

Nov 27, 2021
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"it looks like both sides of the diode appear to go to the same node."
- It doesn't look it. One side is on the ground plane and the other is isolated and goes straight into the FM_ANT connector of the tuner.

"Can you post a close up photo of this blue component?"
- Attached. Its silkscreen label reads L001 and the marking on the component reads 4R7K.
 

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davenn

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That component on the side is a diode.

This picture baffles me because it looks like both sides of the diode appear to go to the same node.

Not a diode ... a spark gap device .... it's going across the antenna input

Yup, my multimeter has both continuity and diode test in the same function so I guess its fine. I checked resistance as well, both ways, but nothing!

Yeah, because it's a spark gap device
 

Tha fios agaibh

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A design for lightning protection?
Looking at this photo it looks like this "spark gap" was Unsoldered from upper left right nodes. Not the lower antenna input. If you follow the upper solder joints, you you can see they are connected at upper left.Screenshot_20211216-045942_Chrome~2.jpg
 
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