Advice needed - has a cap leaked or failed?

[suitissue]

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 at https://www.manualslib.com/manual/1064047/Renault-Lan5200wr1.html


Thanks guys, appreciate it

[bob91343]

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.

[bdunham7]

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.

[Renate]

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.

[GLouie]

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.

[sleemanj]

  It looks like they have leaked, not been leaked upon

Err excuse my ignorance, but what is going to leak from a ceramic or tantalum capacitor? 

[sleemanj]

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.

[GLouie]

It seems odd that the corrosion is localized so well to those 2 caps.

[Renate]

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.

[GLouie]

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.