Author Topic: Need help identifying this diode  (Read 7871 times)

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Offline cryptlabs

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Need help identifying this diode
« on: October 31, 2015, 06:08:15 pm »
Hello,

I'm trying to fix my cb radio,  I' need to find a replacement for this diode but I'm not sure,  please help identify the replacement.
The diode is D9.



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Offline AF6LJ

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Re: Need help identifying this diode
« Reply #1 on: October 31, 2015, 06:11:39 pm »
I wish I had seen more of the curcuit but it looks like a garden verity diode used for reverse polarity protection.
Just a silicon diode that is rated high enough current to blow the fuse and survive.
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Online SeanB

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Re: Need help identifying this diode
« Reply #2 on: October 31, 2015, 06:16:36 pm »
D9 you could use a 1N5404 as a replacement. Beefy diode and cheap, and will not blow open before the fuse.
 

Offline Richard Crowley

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Re: Need help identifying this diode
« Reply #3 on: October 31, 2015, 06:20:15 pm »
I agree with AF6LJ that it looks like an ordinary reverse-polarity protection diode. Under normal conditions, it is "out of the circuit".
We have to assume that the current is flowing from right to left if the diode is intended to blow the fuse in case of reverse-polarity.

It is not clear why you want to replace it?  Is it shorted?  Is it open?  How did you determine it needs replacing? How did you test it?

Any diode rated for at least 2A and 16V would work there. For example...
http://www.allelectronics.com/make-a-store/item/1n5822/schottky-rectifier-3a-40v/1.html
 

Offline cryptlabs

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Re: Need help identifying this diode
« Reply #4 on: October 31, 2015, 06:28:16 pm »
Thank you all for the great support.  I'm trying to trace why my cb is not working and i found that this was cracked open,  I tried to remove it and it broke.

 

Online PA0PBZ

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Re: Need help identifying this diode
« Reply #5 on: October 31, 2015, 06:31:41 pm »
I'm trying to trace why my cb is not working and i found that this was cracked open,  I tried to remove it and it broke.

I hate to bring bad news but this diode is only there to blow the fuse when you connect the power reversed, it will normally not prevent the radio from functioning.
Keyboard error: Press F1 to continue.
 

Offline cryptlabs

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Re: Need help identifying this diode
« Reply #6 on: October 31, 2015, 06:35:13 pm »
I'm trying to trace why my cb is not working and i found that this was cracked open,  I tried to remove it and it broke.

I hate to bring bad news but this diode is only there to blow the fuse when you connect the power reversed, it will normally not prevent the radio from functioning.
Its working without it,  but while tracing the issue i found that this was cracked. There was a trace that was cut and burned that i fixed and it works now, but my signal meter is not working. I'm trying to replace the bad parts.

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Offline T3sl4co1l

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Re: Need help identifying this diode
« Reply #7 on: October 31, 2015, 06:36:08 pm »
If you want something closer,
http://www.digikey.com/product-detail/en/10A01-T/10A01CT-ND/1922678
is probably much closer to the original than even necessary.

Looks like input reverse protection?  If you want something way more fancy than deserved, you can put a TVS in there too (overvoltage protection).  They make 'em in the same size and similar (forward) rating, but not nearly a similar price. :o http://www.digikey.com/product-detail/en/30KPA30A/30KPA30ACT-ND/2699740

Tim
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Offline cryptlabs

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Re: Need help identifying this diode
« Reply #8 on: October 31, 2015, 06:36:40 pm »
Can i use one of these diodes?  I tried to find the same part but its hard to find because my radio is old.

 

Offline T3sl4co1l

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Re: Need help identifying this diode
« Reply #9 on: October 31, 2015, 06:38:10 pm »
6A01 is very similar.

If the original cracked, it's likely a smaller one will only crack faster, under the same stress.  Make sure it's fused, so when the diode is doing its reverse-protection duty, it's able to burn a fuse rather than the diode.

Tim
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Offline cryptlabs

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Re: Need help identifying this diode
« Reply #10 on: October 31, 2015, 06:44:38 pm »
6A01 is very similar.

If the original cracked, it's likely a smaller one will only crack faster, under the same stress.  Make sure it's fused, so when the diode is doing its reverse-protection duty, it's able to burn a fuse rather than the diode.

Tim
It wasn't because of stress,  a friend of mine connected the radio in the wrong way or something back then and the radio was damaged.  I'm trying to bring it back to life.
 

Offline cryptlabs

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Re: Need help identifying this diode
« Reply #11 on: October 31, 2015, 06:46:18 pm »
I have many other diodes also,  whats the best replacement for this?  I want it to be the same as it was.

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Offline cryptlabs

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Re: Need help identifying this diode
« Reply #12 on: October 31, 2015, 06:48:58 pm »
I wish I had seen more of the curcuit but it looks like a garden verity diode used for reverse polarity protection.
Just a silicon diode that is rated high enough current to blow the fuse and survive.
I have uploaded the full circuit.

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Offline AF6LJ

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Re: Need help identifying this diode
« Reply #13 on: October 31, 2015, 06:51:04 pm »
I wish I had seen more of the curcuit but it looks like a garden verity diode used for reverse polarity protection.
Just a silicon diode that is rated high enough current to blow the fuse and survive.
I have uploaded the full circuit.

Sent from my SM-N915F using Tapatalk

I saw that;
What parts are not working right now??
Sue AF6LJ
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Offline cryptlabs

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Re: Need help identifying this diode
« Reply #14 on: October 31, 2015, 06:54:22 pm »
I wish I had seen more of the curcuit but it looks like a garden verity diode used for reverse polarity protection.
Just a silicon diode that is rated high enough current to blow the fuse and survive.
I have uploaded the full circuit.

Sent from my SM-N915F using Tapatalk

I saw that;
What parts are not working right now??
The signal meter LED's,  in the service manual it says that i have to check this.


How can i check if its dead,  should i just check for voltage output?

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Offline Richard Crowley

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Re: Need help identifying this diode
« Reply #15 on: October 31, 2015, 07:12:54 pm »
It wasn't because of stress,  a friend of mine connected the radio in the wrong way or something back then and the radio was damaged. 
That is the very DEFINITION of "stress" in electronic terms.  It was connected with reverse-polarity power. If a proper-sized fuse was installed, the diode should have blown the fuse and protected the rest of the circuit.  But apparently something went wrong. Somebody put in a fuse with a higher rating and/or the diode failed under load.

Are you implying that everything else works OK?  It transmits OK, and receives OK, and changes channel, etc. etc.?
It seems unusual that only the signal-strength meter circuit would have been damaged.

If that TL489C chip is blown, you may have a hard time finding a replacement in single quantities.
You may have to replace it with an LM3914 or AN6884, etc.
 

Offline cryptlabs

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Re: Need help identifying this diode
« Reply #16 on: October 31, 2015, 07:17:17 pm »
It wasn't because of stress,  a friend of mine connected the radio in the wrong way or something back then and the radio was damaged. 
That is the very DEFINITION of "stress" in electronic terms.  It was connected with reverse-polarity power. If a proper-sized fuse was installed, the diode should have blown the fuse and protected the rest of the circuit.  But apparently something went wrong. Somebody put in a fuse with a higher rating and/or the diode failed under load.

Are you implying that everything else works OK?  It transmits OK, and receives OK, and changes channel, etc. etc.?
It seems unusual that only the signal-strength meter circuit would have been damaged.

If that TL489C chip is blown, you may have a hard time finding a replacement in single quantities.
You may have to replace it with an LM3914 or AN6884, etc.
Thanks for explaining, you guys are great [emoji4],  Electronics is my hobby. I can get the same IC.  The radio transmits and receives ok.  Its the s meter that doesn't work and there's one led that lights up and is dim.

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Offline AF6LJ

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Re: Need help identifying this diode
« Reply #17 on: October 31, 2015, 07:18:19 pm »
It wasn't because of stress,  a friend of mine connected the radio in the wrong way or something back then and the radio was damaged. 
That is the very DEFINITION of "stress" in electronic terms.  It was connected with reverse-polarity power. If a proper-sized fuse was installed, the diode should have blown the fuse and protected the rest of the circuit.  But apparently something went wrong. Somebody put in a fuse with a higher rating and/or the diode failed under load.

Are you implying that everything else works OK?  It transmits OK, and receives OK, and changes channel, etc. etc.?
It seems unusual that only the signal-strength meter circuit would have been damaged.

If that TL489C chip is blown, you may have a hard time finding a replacement in single quantities.
You may have to replace it with an LM3914 or AN6884, etc.
This.....
Sue AF6LJ
Test Equipment Addict, And Proud Of It.
 

Offline cryptlabs

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Re: Need help identifying this diode
« Reply #18 on: October 31, 2015, 07:19:30 pm »
It wasn't because of stress,  a friend of mine connected the radio in the wrong way or something back then and the radio was damaged. 
That is the very DEFINITION of "stress" in electronic terms.  It was connected with reverse-polarity power. If a proper-sized fuse was installed, the diode should have blown the fuse and protected the rest of the circuit.  But apparently something went wrong. Somebody put in a fuse with a higher rating and/or the diode failed under load.

Are you implying that everything else works OK?  It transmits OK, and receives OK, and changes channel, etc. etc.?
It seems unusual that only the signal-strength meter circuit would have been damaged.

If that TL489C chip is blown, you may have a hard time finding a replacement in single quantities.
You may have to replace it with an LM3914 or AN6884, etc.
This.....
?

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Offline AF6LJ

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Re: Need help identifying this diode
« Reply #19 on: October 31, 2015, 08:55:05 pm »
Make sure the chip has its supply voltage, if it does and there is no meter output check the chip's input for a signal. For signal strength it will rely on the AGC voltage since that is proportional to the incoming signal.

If the chip doesn't have its supply voltage look for why it is not there.
Sue AF6LJ
Test Equipment Addict, And Proud Of It.
 

Offline cryptlabs

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Re: Need help identifying this diode
« Reply #20 on: October 31, 2015, 11:35:05 pm »
Make sure the chip has its supply voltage, if it does and there is no meter output check the chip's input for a signal. For signal strength it will rely on the AGC voltage since that is proportional to the incoming signal.

If the chip doesn't have its supply voltage look for why it is not there.
Ok,  ill try that. 
Why the radio works even after i have removed the diode?

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Offline karoru

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Re: Need help identifying this diode
« Reply #21 on: October 31, 2015, 11:45:33 pm »
It works because only purpose of that diode is to create a path for a current to flow before fuse breaks when you connect the voltage backwards. It doesn't play any role with correct polarity on voltage supply. Only difference you could see without that diode is that now when you'll connect your power supply backwards, the rest of the circuit will act as an awesome silicon circuit breaker and fry a bit (with maybe some of magic smoke escaping, but not often) before your good old piece of wire encapsulated in glass&sand starts to work.
 

Offline Richard Crowley

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Re: Need help identifying this diode
« Reply #22 on: October 31, 2015, 11:51:58 pm »
Why the radio works even after i have removed the diode?

Under normal conditions, it is "out of the circuit".

HOWEVER, with no diode there, next time you connect reverse-polarity to the gadget, you will completely fry it and turn it into a doorstop.
The purpose of the diode is to take all the reverse current directly to ground in order to BLOW the fuse and protect the rest of the circuit.
 

Offline karoru

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Re: Need help identifying this diode
« Reply #23 on: October 31, 2015, 11:54:45 pm »
HOWEVER, with no diode there, next time you connect reverse-polarity to the gadget, you will completely fry it and turn it into a doorstop.
I've also used the frying metaphore, I wonder why the cooking technique used to explain that is so specific. Why aren't electronic gadgets roasted, or to use another word, braised? We're stuck on unhealthy terminology;p
 

Offline AF6LJ

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Re: Need help identifying this diode
« Reply #24 on: October 31, 2015, 11:58:31 pm »
Make sure the chip has its supply voltage, if it does and there is no meter output check the chip's input for a signal. For signal strength it will rely on the AGC voltage since that is proportional to the incoming signal.

If the chip doesn't have its supply voltage look for why it is not there.
Ok,  ill try that. 
Why the radio works even after i have removed the diode?

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The diode only conducts when the radio is hooked up backward.
That diode is suppose to conduct only when the radio is hooked up[wrong, it conducts and the fuse blows protecting the rest of the radio.
Sue AF6LJ
Test Equipment Addict, And Proud Of It.
 


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