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I have a CR-814 AM/FM/Cassette stereo in my 945T. This stock unit has suddenly picked up a low-tone, medium volume buzzing or humming noise only when the headlights are turned on.
There is no noise with just the park lights on, or if the lights are turned off.
There is no change in the noise when the engine is turned off.
The buzzing tone is at a set volume and can't be adjusted up or down. Only fixes are to turn the radio off or turn off the headlights.
This annoying static buzzing only occurs with the radio is turned on and the headlights are illuminated.
Any ideas folks?
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Interesting.
Since the tone is static and doesn't seem to change with engine on/off (and with it rpm); I would exclude stuff like ignition and alternator. And sice the tone is present at a fixed volume, regardless of volume setting, I'd say the source of the hum is within the radio.
The already mentioned possible arcing inside the headlight switch is not something I'd consider. A bad contact would lead to intermittent and or unstable arcing, nothing like a steady, fixed tone.
So what is it then?
If the headlights are on they draw a nice and steady DC-current (they are still incandescent headlights, right?) which can't create a hum. If all electrical connections, including those to ground, are clean and tight, then it's time to look further.
Hmm, I'm going back to the radio. At this age, most likely the electrolytic caps have degraded which - depending on the circuit they're in - could cause hum. Another reason I'm thinking the radio could be the cause is the following passage from this thread:
"For whatever reason, whenever the car lights are first turned on, the radio emits a loud humming noise. This noise gets weaker as the car warms up, eventually disappearing altogether. I've already checked and replaced all the light bulbs to rule that out. Has anyone else experienced this problem? I briefly popped in a Pioneer headunit I had on the shelf and the problem is not present with this radio, only the stock CR-814. "
Since the Pioneer unit doesn't exhibit the same behaviour, I'd say it was very likely the Volvo radio itself causing it.
Have you got access to another radio you can try?
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You're the winner Gray245.
It turns out the actual cause was in fact the stereo unit. I had it for many years from a "trusted" retailer, and I believed the unit would be the last thing defective.
I appreciate your kind consideration and response.
Now, do you know a "trusted" person who can revive this otherwise nice CR-814?
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Hi,
With only headlights on, makes me think of CID headlights. Are yours still stock incandescents?
If not, a B+ choke filter might work.
I know of no one except someone on the board that has not seen the post yet?
You might have to rewrite the thread title or a place a new post altogether.
There are some people that play with the insides of ECU’s on here.
I cannot believe they don’t know someone in something, like the HAM radio world or those with side line hobbies / almost a business!
The dilemma is, if Anyone else that’s dug into this “throwaway world,” doesn’t want to be bothered.
From what I know about electronics ... you can put in a finger thimble!
I have blow up stuff that I took on, as only a challenge.
Mostly I have been a dump site for others as they didn’t want it back anyway!
I use to break stuff up and take it to recycle, but now they charge a small fee!
It’s has curtailed my interest along with proprietary parts or “no user serviceable components inside.”
The days are garage tinkering are waning fast!
I would suspect a capacitor, used as a signal filter, has gone weak on the input side of the power output transistors. Electrolytic Capacitors are notorious for drying out and changing value.
All it takes is one that cost ten cents or free in waste electronics.
In this scenario it’s most likely in a “preamplifier section” ahead of the power amplifier transistors for your speakers.
I think you are saying the “hum” is there without any sounds being processed.
If it was only happening with one part of the unit, say like the radio only, then it could be in the heterodyne circuit for both AM/FM signals and that goes out to the power amplifier circuit.
Same for cassettes or other inputs sources that get driven over to the speakers.
Ok, that exhausted the dust bin holding my brain!
Phil
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Thanks Phil!
Turns out the reliable source I used for reconditioning my CR-814 was not so reliable and when I installed it, an internal amplifier craped out.
Thanks everyone for taking the time to respond to my inquiry. I'm much obliged.
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I don't know anyone specific that I could recommend, but perhaps you could look for someone doing repairs and restorations of old and/or vintage electronics.
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Try an in-line power noise filter to your radio. Old radio noises.
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Dear Townshend Act,
Hope you're well. As the noise is specific to the headlight setting on the headlight switch, I suspect an internal failure of the headlight switch, which causes arcing.
When electric arc welding is done - current passes between the welding rod and the work-piece, melting the welding rod - a "crackling" noise is produced. A micro-arc inside the switch will produce some heat. You may not be able to hear anything, but the radio may "detect" the noise and make it audible.
Remove the switch array panel from the dashboard. Turn on the headlights. See if: (a) there's any noise coming from the headlight switch; (b) the headlight switch gets "warm" or "hot". Noise or heat suggests switch failure.
If you have a hand-held infrared thermometer, take a reading of the switch housing before you turn on the headlights and again, after the headlights have been on for a few minutes. If there's a small arc, it may take a few minutes for the heat to radiate from the failing switch contacts to the switch's housing. The switch housing's temperature should not change much, unless there's an internal failure.
Try cleaning the contacts between the headlight switch and the harness. An aerosol corrosion-remover (e.g., DeOxit) can be used on the wiring harness connector.
Finally, if you have a "known-good" spare headlight switch, swap it for the in-service unit.
The headlight switch (#1362699) is no longer available (NLA), from Volvo, but the part can likely be found at a salvage yard.
Hope this helps.
All that's best for 2021!
Yours faithfully,
Spook
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Thanks Spook. I'm appreciative of all who reached out.
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Makes a buzzing not changed with volume using radio, tape, CD changer when the engine if off yet the headlights are on?
Does the buzzing come out of all speakers, like the dash speakers (from in-radio amp), and the door speakers, using the remote amp.
--
Beh.
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The static sound comes out of all the speakers
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All the time? Radio on, engine off.
Static buzz sound no matter the sound source? Faulty relay?
Same volume no matter your CR-814 volume adjustment
May be a connection to ground?
Can we look at what wiring diagrams are there to see if the headlamp and radio circuits somehow coincide?
Maybe a looksy at the fuse and relay platform behind the ashtray for anything odd?
Mitchell Service Wiring Diagrams
(Copy and paste URL in new browser tab or window.)
http://www.v8volvo.se/mekartips/volvo/index.html
--
Beh.
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