Bmw cluster repair - Page 1
Forum section: electronics / repair

author: _Emil
author_rank: Contributor
timestamp: October 23, 2021, 08:33:51 pm
content: Hello,I have a bmw dashboard which blows fuses instantly when plugged in. There is a short circuit between gnd and 12v supply.I just opened it up and found a burnt component which i need some help to identifyAll help is appreciated

author: Gyro
author_rank: Super Contributor
timestamp: October 23, 2021, 09:44:28 pm
content: It's an ST SM6T30CAY 25.6V 600W bidirectional TVS. It looks as if it stopped a nasty supply spike and sacrificed itself in the process. They fail short unless there's enough energy to blow them apart - it looks as if that one came pretty close to that.https://www.st.com/en/protection-devices/sm6t30cay.htmlYou might want to think back to anything you did recently (jump start?) and check for loose battery connections, earth straps etc. and proper alternator charging voltage.P.S. Please don't even think of just removing it and hoping for the best. It (hopefully) saved the cluster electronics from death, and if a spike like that has happened once, there's no reason why it can't happen again.

author: _Emil
author_rank: Contributor
timestamp: October 24, 2021, 11:29:54 am
content: Car was bought crashed, don't know what it been through after hehe.Desoldered TVS, short circuit in both of them. No more short between gnd and 12v. Dash started right up on bench!Will order new TVS now. Thank you!

author: Gyro
author_rank: Super Contributor
timestamp: October 24, 2021, 12:31:15 pm
content: Ha, anybody's guess then - maybe even an encounter with a welder. [Edit: Or, possibly more likely, the battery being 'forcibly disconnected' while the alternator was running at high rpm! - BMWs with rear mounted batteries have pyro-electric disconnectors].Good news anyway.

author: m3vuv
author_rank: Super Contributor
timestamp: October 24, 2021, 02:57:35 pm
content: once had a workmate stuck a start charger on a mk3 vauxall cavaliar,it set the airbag off,cost him best part of a thousand quid out of his wages!

author: _Emil
author_rank: Contributor
timestamp: October 28, 2021, 05:45:19 pm
content: Quote from: Gyro on October 24, 2021, 12:31:15 pmBST (pyro thing) already replaced, bmw wanted to sell whole "fusebox" but i found the pyro component cheap on Ebay 😁The wireless phone charger is also dead, short circuit... Desoldered this component, and no more short circuitNeed some help identifying it, 26CA overvoltage protection. Could i use the SM6T30CAY i just bought?

author: Gyro
author_rank: Super Contributor
timestamp: October 28, 2021, 06:10:00 pm
content: You're clearly getting the hang of this thing!It's pretty clear evidence that the 12V supply suffered a nasty energy spike when the BST opened up - I guess they don't particularly care what happens to the car electronics after that point.That part is also a bidirectional TVS as you have worked out. This one is a LittlefuseP4SMA27CAP6SMBJ27CA, again a 600W 25.7V (27V typ.) part. It's probably a case of different sub-assembly suppliers having their own favourite parts / supplier pricing arrangements. Yes the SM6T30CAY will be fine.Oh BTW, this is my favourite site for smd part identification...http://www.smdmark.com/en-US/search/code?id=27caI usually look up the full part numbers on the web rather than relying on the embedded PDF datasheet links. Maybe just me being cautious.P.S. Hopefully the ECUs used bigger TVSs, they are usually much larger package parts.

author: _Emil
author_rank: Contributor
timestamp: October 28, 2021, 06:49:26 pm
content: I will try solder a new TVS and see if it works! Hopefully it works without canbusReally appreciate your help! Thank you

author: _Emil
author_rank: Contributor
timestamp: October 29, 2021, 01:38:47 pm
content: Everything up and working now! Thanks again