Need help identifying this diode - Page 1
Forum section: electronics / repair

author: cryptlabs
author_rank: Contributor
timestamp: October 31, 2015, 06:08:15 pm
content: 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.Regards

author: AF6LJ
author_rank: Unknown
timestamp: October 31, 2015, 06:11:39 pm
content: 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.

author: SeanB
author_rank: Super Contributor
timestamp: October 31, 2015, 06:16:36 pm
content: D9 you could use a 1N5404 as a replacement. Beefy diode and cheap, and will not blow open before the fuse.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 31, 2015, 06:20:15 pm
content: 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

author: cryptlabs
author_rank: Contributor
timestamp: October 31, 2015, 06:28:16 pm
content: 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.

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 31, 2015, 06:31:41 pm
content: Quote from: cryptlabs on October 31, 2015, 06:28:16 pmI 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.

author: cryptlabs
author_rank: Contributor
timestamp: October 31, 2015, 06:35:13 pm
content: Quote from: PA0PBZ on October 31, 2015, 06:31:41 pmIts 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.Sent from my SM-N915F using Tapatalk

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 31, 2015, 06:36:08 pm
content: If you want something closer,http://www.digikey.com/product-detail/en/10A01-T/10A01CT-ND/1922678is 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.http://www.digikey.com/product-detail/en/30KPA30A/30KPA30ACT-ND/2699740Tim

author: cryptlabs
author_rank: Contributor
timestamp: October 31, 2015, 06:36:40 pm
content: Can i use one of these diodes? I tried to find the same part but its hard to find because my radio is old.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 31, 2015, 06:38:10 pm
content: 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

author: cryptlabs
author_rank: Contributor
timestamp: October 31, 2015, 06:44:38 pm
content: Quote from: T3sl4co1l on October 31, 2015, 06:38:10 pmIt 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.

author: cryptlabs
author_rank: Contributor
timestamp: October 31, 2015, 06:46:18 pm
content: I have many other diodes also, whats the best replacement for this? I want it to be the same as it was.Sent from my SM-N915F using Tapatalk

author: cryptlabs
author_rank: Contributor
timestamp: October 31, 2015, 06:48:58 pm
content: Quote from: AF6LJ on October 31, 2015, 06:11:39 pmI have uploaded the full circuit.Sent from my SM-N915F using Tapatalk

author: AF6LJ
author_rank: Unknown
timestamp: October 31, 2015, 06:51:04 pm
content: Quote from: cryptlabs on October 31, 2015, 06:48:58 pmI saw that;What parts are not working right now??

author: cryptlabs
author_rank: Contributor
timestamp: October 31, 2015, 06:54:22 pm
content: Quote from: AF6LJ on October 31, 2015, 06:51:04 pmThe 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?Sent from my SM-N915F using Tapatalk

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 31, 2015, 07:12:54 pm
content: Quote from: cryptlabs on October 31, 2015, 06:44:38 pmThat 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.

author: cryptlabs
author_rank: Contributor
timestamp: October 31, 2015, 07:17:17 pm
content: Quote from: Richard Crowley on October 31, 2015, 07:12:54 pmThanks for explaining, you guys are great , 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.Sent from my SM-N915F using Tapatalk

author: AF6LJ
author_rank: Unknown
timestamp: October 31, 2015, 07:18:19 pm
content: Quote from: Richard Crowley on October 31, 2015, 07:12:54 pmThis.....

author: cryptlabs
author_rank: Contributor
timestamp: October 31, 2015, 07:19:30 pm
content: Quote from: AF6LJ on October 31, 2015, 07:18:19 pm?Sent from my SM-N915F using Tapatalk

author: AF6LJ
author_rank: Unknown
timestamp: October 31, 2015, 08:55:05 pm
content: 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.

author: cryptlabs
author_rank: Contributor
timestamp: October 31, 2015, 11:35:05 pm
content: Quote from: AF6LJ on October 31, 2015, 08:55:05 pmOk, ill try that.Why the radio works even after i have removed the diode?Sent from my SM-N915F using Tapatalk

author: karoru
author_rank: Regular Contributor
timestamp: October 31, 2015, 11:45:33 pm
content: 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.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 31, 2015, 11:51:58 pm
content: Quote from: cryptlabs on October 31, 2015, 11:35:05 pmQuote from: Richard Crowley on October 31, 2015, 06:20:15 pmHOWEVER, 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.

author: karoru
author_rank: Regular Contributor
timestamp: October 31, 2015, 11:54:45 pm
content: Quote from: Richard Crowley on October 31, 2015, 11:51:58 pmI'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

author: AF6LJ
author_rank: Unknown
timestamp: October 31, 2015, 11:58:31 pm
content: Quote from: cryptlabs on October 31, 2015, 11:35:05 pmThe 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.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 01, 2015, 12:11:29 am
content: This is one of a few techniques used to attempt to idiot proof the power connection. Others include using a bridge rectifier across the inputs so that it works with power connected either way, and putting the diode in series with the fuze. These two approaches add a diode drop to the power connection, so batteries don't work as long. Engineers learned long ago that polarized plugs and other methods of keeping the power right side up are more easily overcome than most would expect, so protection of some form is often included. As AFJ6LJ mentioned the method used in this radio is susceptable to over-fusing. (What? The fuze blew? Well I'll just put a bigger one in so I can get power up long enough to see what is wrong. Happens all the time. Even to people who should know better). Fortunately the diode often fails shorted which at least protects the rest of the radio.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 01, 2015, 05:06:12 am
content: Quote from: cryptlabs on October 31, 2015, 06:44:38 pmWell, thermal stress I meanTim

author: cryptlabs
author_rank: Contributor
timestamp: November 01, 2015, 12:38:58 pm
content: Quote from: AF6LJ on October 31, 2015, 08:55:05 pmThe chip has 13.8 voltage on vcc, the input has 0.0104 when idle and when i key up it goes to 0.384 approximately.Quote from: T3sl4co1l on November 01, 2015, 05:06:12 am

author: cryptlabs
author_rank: Contributor
timestamp: November 01, 2015, 12:41:27 pm
content: What is the name of the diode in the schematics? I want to check the data sheet. Is this the same :http://www.digchip.com/datasheets/parts/datasheet/922/10E1.php

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 01, 2015, 12:57:58 pm
content: Yes, that looks like it is probably the data sheet for the original diode.But we must ask why that is important?That particular diode was selected for its electrical ratings (voltage and current) but mostly because it was CHEAP. It can be replaced with ANY diode of sufficient voltage and current ratings. And using a diode of greater current rating wouldn't be a bad idea considering past history.And be SURE to use only the rated current for the fuse. Using a fuse of greater current rating will put the gadget at risk all over again.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 01, 2015, 01:06:50 pm
content: Quote from: cryptlabs on November 01, 2015, 12:38:58 pmAssuming you are talking about IC5 (TL489C).Can you affect the display by turning the adjustment VR4? If you turn anything BE SURE to mark carefully where it started so that you can restore it to its original setting. But you should be able to run the display up and down (to some extent) by changing VR4.If you can't make the display change, then IC5 is probably "blown". Be grateful that so much more of the radio still functions.

author: cryptlabs
author_rank: Contributor
timestamp: November 01, 2015, 01:09:40 pm
content: Quote from: Richard Crowley on November 01, 2015, 12:57:58 pmOK thanks for clearing this. So which diode should i use from the photo i uploaded should i use the 6A01?And can you help me with the signal meter issue?

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 01, 2015, 01:14:45 pm
content: Quote from: cryptlabs on November 01, 2015, 01:09:40 pmYes, as @T3sl4co1l said...Quote from: T3sl4co1l on October 31, 2015, 06:38:10 pm

author: cryptlabs
author_rank: Contributor
timestamp: November 01, 2015, 01:30:17 pm
content: Quote from: Richard Crowley on November 01, 2015, 01:14:45 pmI tried to move it but nothing happens.This is from the manualLED 4 is always stuck

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 01, 2015, 01:36:39 pm
content: That would be a very good indication that IC5 (TL489C) has been fried by the reverse-voltage accident.If you can get a replacement, then that seems like the clear path to restoration.

author: AF6LJ
author_rank: Unknown
timestamp: November 01, 2015, 01:51:06 pm
content: Finding this part may be a challengehttps://www.google.com/?gws_rd=ssl#q=TL489C++ICYou might check on E-Bay for this part, often times you can find new old stock parts there...

author: macboy
author_rank: Super Contributor
timestamp: November 03, 2015, 01:49:14 pm
content: That TL489 is fried. There are a few TL489CP on ebay from Asian sellers, but as always, you don't know the history of those parts. They may be new old stock or may be used parts pulled from old boards.As for that diode, don't worry about an exact replacement, it is a very non-critical application (though a very important one). I'd use a 1N5404 that you have. Make sure the fuse that is installed is the correct type. From the schematic it is a 2A fast acting fuse. Do not use a slow-blow.