Advice needed - has a cap leaked or failed? - Page 1
Forum section: electronics / repair

author: suitissue
author_rank: Newbie
timestamp: January 26, 2022, 05:50:28 pm
content: Hi, looking for some advice - I've dabbled in repair over the years and replaced and re-flowed components, but not brilliant on the whole testing and diagnosing bit!I have a car HU which has no amplifier output when cold, albeit when hot air is flowed over the board works perfectly, and has been developing this fault over months, with no output until warmth is applied. Have taken apart the board and immediately two SMDs had corrosion on, other than that board was perfect. The board has been heated to re-flow and corrosion removed but the issue is still there with the same symptoms.In my mind I'm looking at either the big cap has failed and leaked over these SMDs, or they're faulty themselves.If it's any help, board schematics are athttps://www.manualslib.com/manual/1064047/Renault-Lan5200wr1.htmlThanks guys, appreciate it

author: bob91343
author_rank: Super Contributor
timestamp: January 26, 2022, 06:25:09 pm
content: Don't assume the problem is caused by a capacitor. You need to get out the usual tools and inspect the circuit. You need a signal generator and an oscilloscope and a voltmeter and, of course, the diagrams.You could have one or more bad components or connections, and making assumptions will likely be a waste of time.

author: bdunham7
author_rank: Super Contributor
timestamp: January 26, 2022, 06:36:26 pm
content: Your schematic is unreadable, at least by me. If you could identify those capacitors, it would help. It looks like they have leaked, not been leaked upon. If you can't ID them, you might try just measuring the voltage across them in operation and then put in a physically similar SMD tantalum to see if you problem is resolved. I don't like jumping to conclusions, but experience tells me that your symptoms and the appearance of those caps make it at least somewhat likely that they are the issue.

author: Renate
author_rank: Super Contributor
timestamp: January 26, 2022, 06:44:17 pm
content: I presume that that 13 pins (plus the next hidden row) that I see in the 1st photo is the power amplifier chip?I see a lot of grunge on the right side. You should clean that. It could be power down or mute. You should check the critical voltages there.I'd guess that the big cap is ok except that someone got too enthusiastic with the white goop at the factory.

author: GLouie
author_rank: Regular Contributor
timestamp: January 27, 2022, 10:14:34 pm
content: Manualslib schematic download is fine for me.I have no advice, but for reference the corroded caps are C239 and C241. The large power cap is C199 and the amplifier is IC110, a TDF8546.Maybe a multilayer board - could have a problem you can't see.Partial schematic attached.

author: sleemanj
author_rank: Super Contributor
timestamp: January 27, 2022, 10:53:12 pm
content: Quote from: bdunham7 on January 26, 2022, 06:36:26 pmErr excuse my ignorance, but what is going to leak from a ceramic or tantalum capacitor?

author: sleemanj
author_rank: Super Contributor
timestamp: January 27, 2022, 10:56:42 pm
content: It should be a simple job to pick off the silastic and inspect the electrolytic for signs of leakage. Given the lack of corrosion in general that would indicate ingress of water or other substance from external factors, that would be my first instinct as an easy thing to eliminate.

author: GLouie
author_rank: Regular Contributor
timestamp: January 27, 2022, 11:05:35 pm
content: It seems odd that the corrosion is localized so well to those 2 caps.

author: Renate
author_rank: Super Contributor
timestamp: January 28, 2022, 12:34:14 am
content: So the big chip is 27 pin and I can see 13 pins. That means the back row is 14 pins and the right of the photo is a pin 2 with lots of gunk on it and it's the standby pin and it running on a 91k resistor.No, I'm sure what polarity it's working on but this looks like a smoking gun to me. Look at the voltage there.

author: GLouie
author_rank: Regular Contributor
timestamp: January 28, 2022, 02:11:23 am
content: Blue gunk on pin 2? Also blue gunk on the silastic under the big power cap. However, the corroded caps don't show any blue gunk.We are also assuming OP is correct that only the power amp has this problem.