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Thread: Delco Radio Repair - Right-Channel out / static / thumping noise....

  1. #31
    Senior Member white89euro's Avatar
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    Another cool fix-it thread from David. Thanks David! I'll bet many other GM forums would like to see this thread too. You may want to consider posting your info to a how-to web site. I can't think of the names of any right now, but I'm sure you've seen them.

    Great work!
    George



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    David have you ever dealt with the CDM Box from the 86-96 units? There were a lot of issues with the CDM Box( Tuner amp section ) of the head unit, the Box was easily replaced when it failed so that you didn't have to replace the entire unit.. A lot of the time the tuner seemed to quit, or the power would be inop..

    Just curious if you had ever deal with any of those older 5 Band CDM units used with steering wheel controls more than most of the time...

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    Perfect. I literally have a stack of these that need that fixed. But my main concern is my 1982 symphony sound. As long as this repair does not affectbthe awesome bass responce of the unit then this will be awesome. My whole right channel is weak. And pops and cracks an carrys on sometimes but usually clears up. But the sound is noticably louder on left. The other thing i want to do is figure out a way to boost fm reception. My buddys radio i got him can strech about 80 miles of clear reception. For the most part. Mine goes about 60 but it is weak. Idk ithe early radios werent as strongor if there is something i can do to up the reception. I also would like to find a way to install a "fine tune" knob for those times you get crosses between neighboring channels.

  4. #34
    Senior Member turbokinetic's Avatar
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    Quote Originally Posted by cody1234 View Post
    Perfect. I literally have a stack of these that need that fixed. But my main concern is my 1982 symphony sound. As long as this repair does not affectbthe awesome bass responce of the unit then this will be awesome. My whole right channel is weak. And pops and cracks an carrys on sometimes but usually clears up. But the sound is noticably louder on left. The other thing i want to do is figure out a way to boost fm reception. My buddys radio i got him can strech about 80 miles of clear reception. For the most part. Mine goes about 60 but it is weak. Idk ithe early radios werent as strongor if there is something i can do to up the reception. I also would like to find a way to install a "fine tune" knob for those times you get crosses between neighboring channels.
    The capacitor fix won't change the bass response at all. I'm not an expert on tuners - not sure what can be done about the distance reception!

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    I have son boosters but it helps more if the reception is already good.

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    And on this subject. Would anybody know where exactly the pre amp stage is.. Volume controlled area of pre amp I know older stereos its typically the lines on the control knob itself but I bet the Delco symphony sound is different.. I would like to add my own line output.. I also want to add an auxiliary that cuts out the am fm part. And if anybody has any recommendations on sheilded wires to cancel out interference on that. Or if its all within the radio I that would make a difference.

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    Senior Member Century7667's Avatar
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    Quote Originally Posted by cody1234 View Post
    And on this subject. Would anybody know where exactly the pre amp stage is.. Volume controlled area of pre amp I know older stereos its typically the lines on the control knob itself but I bet the Delco symphony sound is different.. I would like to add my own line output..
    It would be very cool if someone could answer that. It would allow you preserve the head unit, and feed a powerful power amp. I've search and search, and haven't found an answer.

    I never developed my electronic skills sufficiently to figure out how to trace the circuit boards. If we could just locate a schematic......

    Ken T.

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    Senior Member SegaGT's Avatar
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    " I would like to add my own line output.. "
    " I never developed my electronic skills sufficiently to figure out how to trace the circuit boards. If we could just locate a schematic......"

    The "fast & nasty" method to find the post EQ, pre-driver/output stage is to use an old school "Crystal headphone". You know the old mono type that were tan in color and were used on small TV sets or AM radios back in the day. We used that trick in AV when you don't have schematics or a scope handy. DC/AC doesn't hurt the headphone and touching the tip to the traces is all it takes to "listen" for the signal.

    Soldering on some RCA leads from there would be cool but I think most people take the easy way out and get or make a line level adapter that just runs off the speaker level outputs...

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    That's what I have now. The line converter. But . Why tune down an amplified signal. I am hoping to cleaner sound if I can find the pre amp stage.. I will just have to check into it. I have fiddled with these things some. The one thing I want to figure too. Sometimes when I mess with it turned on there's a part that will blow and it wont turn on again. Usually on amp board. It usually shows the time still but nothing else. . At one time I actually succeded in building my own 8 track Delco out of a 1990 Pontiac Delco cassette deck. Was not pretty and the 8 track stuck out the back and wouldn't fit into the dash. The good part was the Delco already has a 12 volt regulator in it so the speed ran correctly. If I could find a picture.. This was back in 2011 I made that. One different thing I also did before is I put the wrong heads in the cassette player. Basically made well. Never finished it due to complications. Was making a car radio that could record cassette tapes.

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    Quote Originally Posted by SegaGT View Post
    " I would like to add my own line output.. "
    " I never developed my electronic skills sufficiently to figure out how to trace the circuit boards. If we could just locate a schematic......"

    The "fast & nasty" method to find the post EQ, pre-driver/output stage is to use an old school "Crystal headphone". You know the old mono type that were tan in color and were used on small TV sets or AM radios back in the day. We used that trick in AV when you don't have schematics or a scope handy. DC/AC doesn't hurt the headphone and touching the tip to the traces is all it takes to "listen" for the signal.

    Soldering on some RCA leads from there would be cool but I think most people take the easy way out and get or make a line level adapter that just runs off the speaker level outputs...
    Believe it or not I have a couple of these headphones.. Time to have fun I suppose..

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    I seem to have a problem here.. It seems the 1982 Cadillac radios amp board is completely different

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    Well the 1988 Cadillac radio is like this. The common one. I guess the 82 is an oddball. .

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    Quote Originally Posted by SegaGT View Post
    " I would like to add my own line output.. "
    " I never developed my electronic skills sufficiently to figure out how to trace the circuit boards. If we could just locate a schematic......"

    The "fast & nasty" method to find the post EQ, pre-driver/output stage is to use an old school "Crystal headphone". You know the old mono type that were tan in color and were used on small TV sets or AM radios back in the day. We used that trick in AV when you don't have schematics or a scope handy. DC/AC doesn't hurt the headphone and touching the tip to the traces is all it takes to "listen" for the signal.

    Soldering on some RCA leads from there would be cool but I think most people take the easy way out and get or make a line level adapter that just runs off the speaker level outputs...
    I remember those. I had one as a kid with my transistor radio I got for my 8th birthday. I'm so old....

    Ken T.

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    Quote Originally Posted by Century7667 View Post
    I remember those. I had one as a kid with my transistor radio I got for my 8th birthday. I'm so old....

    Ken T.
    Not old, just experienced!
    BTW I have seen your electronic skills, you could tackle most anything successfully.
    Speaking of,.. Do I see an "upgrade" included in your next LIM replacement?

  15. #45
    Senior Member Century7667's Avatar
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    Quote Originally Posted by SegaGT View Post
    Not old, just experienced!
    BTW I have seen your electronic skills, you could tackle most anything successfully.
    Speaking of,.. Do I see an "upgrade" included in your next LIM replacement?
    Thank you. I'm trying to get to the LIM for the '95 as quickly as I can, but I need to complete the timing chain job on my S10. Unfortunately, I got distracted by a clothes dryer repair and I discovered a small coolant leak on the S10 during tear down. The timing chain hasn't been too big a deal so far, just been distracted...

    But, that next LIM job is desperately needed on the '95, primarily for the oil pump drive o-ring which is *totally* gone. Oil is EVERYWHERE. That car is my daily driver, and it's really hurting. Can't do an upgrade on it though, Fort Bend county under tight emissions controls, so she has to pass. No upgrades unless I can find a sweet 1990 Century or older. I'd love to drive one of the older ones like David's but they are quite rare, and a clean one is even rarer still.

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