Author Topic: Can't read burnt cap. Any ideas?  (Read 940 times)

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Offline tehmagicsmoke

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Can't read burnt cap. Any ideas?
« on: October 04, 2018, 03:01:14 am »
Trying to repair a battery charger for my brothers r.v.
There's 1 little ceramic disc cap that is burnt completely brown. I can't read the number.
At first I thought it said 100 or 103 but it is completely illegible under any color light and with my $50 digital microscope or magnifying glass.
The back leg separated upon removal. I held it together with tweezers to attempt to test it.
After several years it reads anywhere from 60-205pf.
I have stuck 2 100pf caps in parallel thinking that would be safer to go under than over.
I don't have the knowledge to deconstruct the circuit to do the math to figure out what it needs. Though I am pretty good at math.
If anyone has any better suggestions or constructive criticism please feel free to let me know.
I didn't know what term to search for as I assume this topic has already been covered. And I don't know what term to search for to help me deconstruct the circuit to figure out what it needs. Thanks again everyone!
 

Offline JustMeHere

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Re: Can't read burnt cap. Any ideas?
« Reply #1 on: October 04, 2018, 03:04:28 am »
Pictures please
 

Offline tehmagicsmoke

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Re: Can't read burnt cap. Any ideas?
« Reply #2 on: October 04, 2018, 03:20:52 am »
I didn't get any pictures while it was apart. If someone has skills and wants to take a look at the circuit and could tell me what it needs I can take it apart again. I got some pics of the cap I will post, but it is illegible.
 

Offline dcarr

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Re: Can't read burnt cap. Any ideas?
« Reply #3 on: October 04, 2018, 05:22:26 am »
Posting a picture of the circuit is probably your best bet.
 

Offline coromonadalix

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Re: Can't read burnt cap. Any ideas?
« Reply #4 on: October 04, 2018, 10:26:24 am »
Hi   you need to know in wich section this cap has blown, for an example you can try 0.1 uf / 100v cap, normally used in decoupling, parallel with dc supply lines etc ...

But posting pictures if you can would help you faster
 

Offline tehmagicsmoke

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Re: Can't read burnt cap. Any ideas?
« Reply #5 on: October 04, 2018, 11:37:55 pm »
Thank you for the reply. I'm about to tale it apart again to get some pictures and put a 471 cap in there. I stuck it under my microscope and tried different colored lights and different angles. O can't tell of it says 471 or 473!  Should have some pictures up before the end of the day.

I also forgot to test for a short to ground, hopefully that isn't why it failed!

With the 200pf cap it was putting out 3 volts. Hopefully the 471 cap will bring it up to 13 volts.
 

Offline tehmagicsmoke

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Re: Can't read burnt cap. Any ideas?
« Reply #6 on: October 05, 2018, 07:20:18 pm »
Here's the pics. The microscope was in focus when I took the picture, so I don't know why these appear blurry.
 

Offline tehmagicsmoke

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Re: Can't read burnt cap. Any ideas?
« Reply #7 on: October 05, 2018, 07:38:39 pm »
Here are more pictures of the board. I replaced the cap with the 2 orange caps in the middle of the first picture.

The bottom side of the board under that cap has a black permanent marker mark between the legs.

The pictures of the transistors should be in the correct order from left to right.

I don't know why there is nail polish on the trimmer potentiometers. I suspect someone opened it and instead of finding the burnt cap they tried adjusting the little pots. But there were rivets holding the shell together. It's possible they replaced the rivets.
 

Offline tehmagicsmoke

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Re: Can't read burnt cap. Any ideas?
« Reply #8 on: October 05, 2018, 07:40:19 pm »
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Offline tehmagicsmoke

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Re: Can't read burnt cap. Any ideas?
« Reply #9 on: October 05, 2018, 07:41:05 pm »
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Offline tehmagicsmoke

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Re: Can't read burnt cap. Any ideas?
« Reply #10 on: October 05, 2018, 07:41:56 pm »
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