Help with mistery damage? substance? - Page 1
Forum section: electronics / repair

author: MisterSPC700
author_rank: Newbie
timestamp: November 18, 2021, 04:22:20 am
content: Hello. I'm currently trying to repair a Sony PVM 1354Q. While inspecting the main board, I came across an IC (MC14538BF), which is a monostable multivibrator, that looked damaged. I first thought that it was some kind of heat-related damage. But then, I noticed that some components near to that chip had a little bit of that "bubbly substance". I thought that maybe was some kind of leaky cap but I don't see any other kind of damage around that would be consistent with damage done by a leaking cap. The same type of IC is also present at some other parts of the board and some of them have that "substance", either at the top or between the pins. I also stumbled upon a forum post of someone who was recapping his PVM (different model than mine) and he shows a photo of the same IC's with the same thing. He theorizes that it is heat damage done by a nearby transistor that has no heatsink but I doubt it since the other IC's that exhibit the same thing are in places where there are no transistors or any other component that could generate a lot of heat. What could it be? I assume that the chips work fine but in the case of having to replace them, I'm having trouble finding stock since they are obsolete. Could I replace them with another variant of the IC that is more easily obtainable? Thanks!

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: November 19, 2021, 06:49:32 am
content: This looks like some thin conformal coating that was misapplied or is degrading with age (not heat affected).

author: George Edmonds
author_rank: Frequent Contributor
timestamp: November 19, 2021, 07:23:48 am
content: It has the appearance of leaking electrolytic capacitor electrolyte, this is both conductive and highly corrosive.George G6HIG Dover UK

author: Xenon
author_rank: Contributor
timestamp: November 19, 2021, 09:48:19 am
content: I agree with Chickenheadknob.Look at the light-blue cap on the 5th photo. It has a curtain of this coating hanging between its legs.

author: Haenk
author_rank: Super Contributor
timestamp: November 19, 2021, 10:27:40 am
content: Look at the wavy pattern on the PCB - that PCB certainly has been coated with "stuff".

author: t1d
author_rank: Super Contributor
timestamp: November 19, 2021, 12:38:09 pm
content: Quote from: Xenon on November 19, 2021, 09:48:19 amXenon has a point about the "curtain." You might want to probe that with a toothpick. Maybe record a video of it, while you poke at it (gently,) because you are likely only going to get one chance at it. Meaning, if it all crumbles off at once, and you are not sure what you saw, you could review the video. If it is a curtain, then I vote for it being a coating.You could also test the substance with plain water on a Q-tip. If it is leakage from an e-cap, plain water should get it to at least move/smear. If it is a coating, it should not react at all.You often hear about e-caps leaking. But, I have seen them out-gas, too. This is a little different than them spewing their liquid contents, due to the build up of internal pressure. Out-gassing is more like a smoke, or fog. It can coat components on both the top and bottom of the PCB. It can also have a limited pattern, caused by airflow in a particular direction. Out-gassing + humidity + heat = bubbling = Maybe?If it is out-gassing and you don't find a bad e-cap, it is possible someone changed the cap, but didn't clean the board.If it is sticky, might it be a spilled Sprite/7-Up?I hope that gives you some ideas to think on. Please do post your final determination of what it is.

author: m k
author_rank: Super Contributor
timestamp: November 19, 2021, 05:27:50 pm
content: Quote from: t1d on November 19, 2021, 12:38:09 pmMy guess is soap.