GM delco eight track 1970s 80bfmt1 problem - Page 2 - diyAudio
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Old 3rd October 2012, 12:38 AM   #11
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Tantalum capacitors are rarely used in values below 1uf. They are used where high capacitance in a small package is required. They are very sensitive to over-voltage and reverse voltage.

The electrolytic capacitors can be damaged in the same ways as mentioned above.

Are you sure that this radio wasn't connected to the power source with reverse polarity?
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Old 3rd October 2012, 01:07 AM   #12
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Hi Perry,
thanks for ya time,Wiring was followed as embossed on the unit case,burning out didnt start until i connected a 12v 7 amp psu.The unit hasnt been on since 1987..
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Old 3rd October 2012, 04:42 AM   #13
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Someone may have connected it with reverse polarity before you received it.

The radio should work without those capacitors unless they're shorted. For testing, you can install virtually any cap with a value near the rating of the original.

Do you get any response from the radio if you connect a speaker?
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Old 3rd October 2012, 05:14 PM   #14
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The radio was new ,and worked ok,then sat in the car until i stripped it all down,it was when i reconnected i got smoke,first one tantalum cap,then another then the electrolyte cap.
I get nothing,and i mean not even a crackle with speakers connected..
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Old 3rd October 2012, 05:45 PM   #15
maylar is offline maylar  United States
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Maybe it's just the lighting, but it looks to me like the case of that electrolytic cap is bulging. Tell tale sign of reverse polarity being applied.
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Old 3rd October 2012, 06:45 PM   #16
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Quote:
Originally Posted by maylar View Post
Maybe it's just the lighting, but it looks to me like the case of that electrolytic cap is bulging. Tell tale sign of reverse polarity being applied.
Dave its not the light,it popped on the bench ,then hissed,.However i think it shorted out on the case,it was sitting on,big mistake.
i ordered another one and a couple of tantalums .Im concerned that Perry said i should be getting something even with the bits blown ,but im getting nothing.. Thanks for ya time
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Old 14th October 2012, 08:35 AM   #17
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I have now replaced the parts with 2 ITT 6.8/16v tants,and the 1000uf/25v capicitor.
Good news,its now not burning out when power gets to them,The downside is ,still no sound,not even a crackle.
Could it be a dry joint somewhere,is it advisable to go over all the old solder with my iron.
What is next i can test,i just bought a proper circuit tester.
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Old 14th October 2012, 09:11 AM   #18
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I doubt resoldering all the joints will help. Did you test it in both radio and tape modes? No output at all suggests to me that a problem exists in the audio section, after either the radio or tape preamp sections. Without service literature, critical voltage checks and signal injection/tracing would likely be the most practical approach. Hopefully others here have more ideas.
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Old 14th October 2012, 01:15 PM   #19
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It likely has a mechanical power switch on the volume control. Do you see the voltage at the switch, switching on and off on the second terminal of the switch as you switch the radio on/off?
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Old 17th October 2012, 12:34 PM   #20
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Found a working 8 track cartridge.unit powers up, motors spin,no burning or smoking now ,"thanks all"...just no sound,crackle or otherwise,on either radio or 8 track..
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