Audi A6 control unit repair - Page 1
Forum section: electronics / repair

author: Balefati
author_rank: Contributor
timestamp: August 27, 2024, 07:22:22 am
content: Hello everyonei got a broken control unit for the steering column lock of my Audi A6 4F5 C6. Upon opening it i smelled a very faint hint of burn from one area of the board. One solder joint of that component looks burnt to me (red arrow). The top of it also looks a little burnt. I tried to capture it as good as possible. Also scraped the coating from the components nearby if that helps. I measured it in circuit and got the following measurements: around 175 ohms when measuring between the "left" leg on the side with two legs and the leg that looks burnt. Voltage drop between those two is 0.250V (in both directions). All other combinations of legs dont give me any readings. Dont know if this is useful since it is in circuit.My question now is: Can anyone identify what that component is and whether its likely that it failed?Please let me know if you need additional information or pictures

author: woody
author_rank: Frequent Contributor
timestamp: August 27, 2024, 07:32:50 am
content: Maybe thishttps://smd.yooneed.one/will help you?

author: daisizhou
author_rank: Super Contributor
timestamp: August 27, 2024, 07:52:07 am
content: Quote from: Balefati on August 27, 2024, 07:22:22 amBAS21 Silkscreen JS LBAS21LT1G SOT23 250V 250mA Switching Diode

author: bborisov567
author_rank: Regular Contributor
timestamp: August 27, 2024, 08:06:28 am
content: Looks like may be the diode for back EMF protection from the coil, given it is close to the relay.

author: Balefati
author_rank: Contributor
timestamp: August 27, 2024, 01:00:22 pm
content: So, would i be able to bridge the contacts and see if it works or would the back EMF fry something done the line. Or is the diode a "just to be sure" thing. I could check if it works and then order the diode.

author: bborisov567
author_rank: Regular Contributor
timestamp: August 27, 2024, 01:19:10 pm
content: Given the way it looks there is no chance to be functional. I would recommend replacing it with another diode that you have at hand and see if the module works. There is a possibility of the MCU output port being damaged by the back EMF if the burned diode has gone to open circuit.

author: Balefati
author_rank: Contributor
timestamp: August 27, 2024, 04:11:58 pm
content: Quote from: bborisov567 on August 27, 2024, 01:19:10 pmSo any diode with a low enough forward voltage will do for testing? Like any through hole diode for example? I have a N4004 diode on hand.

author: bborisov567
author_rank: Regular Contributor
timestamp: August 28, 2024, 07:19:40 am
content: 1N4007, 1N4007 both will be fine for a test.

author: inse
author_rank: Super Contributor
timestamp: August 28, 2024, 07:32:18 am
content: Verify and confirm again the polarity

author: Balefati
author_rank: Contributor
timestamp: August 28, 2024, 09:12:10 am
content: Quote from: inse on August 28, 2024, 07:32:18 amSo the silver ring should be on the side where there is one leg on the SOT23? At least thats what i get from the datasheet of the original diode.

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: August 28, 2024, 09:50:21 am
content: alphabet suédois

author: bborisov567
author_rank: Regular Contributor
timestamp: August 28, 2024, 09:53:32 am
content: Quote from: Balefati on August 28, 2024, 09:12:10 amThat is correct. The pin close to the ring is called Cathode, the other Anode.