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Another ABI boardmaster repair

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Monstermug View Drop Down
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    Posted: 05 Jan 2018 at 6:06pm
Had some time to repair some pcbs over xmas but to my dismay my glorified chip tester decided to bug up and fail self test!  

When turned on I get the following error messages! 

It would then go into the main menu but it would not allow any test to be performed due to the failed self test.

Looking into the manual, I could not find any description to these fault codes.  Looking online didn't help either.  There's literally no documentation on this thing.

I opened it up and had a good look around.  Then it hit me.  The fault weren't codes but actual locations of where the fault could be.  

So P 32/1 91, 92, 93, 90, 95, K32

Actually refers to Resisters@ 32 and 31, Chips at U91, U92, U93, U90, U95 and relay @ K32.

Decided to first test the relay.  That tested good.  Pulled the one next to it and that tested good.  Replaced it with some relays I picked up some time ago as security as I didn't like putting old stuff back.

Next component down the line was @ U90.  This was a SN7438N through hole which was easy to take out and replace.  This did not solve the problem.

U91 -> U95 were all surface mounted chips which I didn't feel like pulling out just to test so I investigated a bit further.  Whist trying to work out what P32/1 was, I saw that the quad flat pack @ U28 had a few pins on the corner covered in what looked like dried manufacturing flux.  

This caused intermittent shorts between adjacent pins.

Using isopropyl and carefully disintegrating it and wiping it clean..

I then tested for continuity and resistance and it looked fine.

Decided to assemble it all back together.

To my relief it fixed the problem

Hope this might help others with the same problem.  Unfortunately, didn't have any time left to repair any pcbs.  Maybe another day Embarrassed

Edited by Monstermug - 05 Jan 2018 at 10:25pm
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DanP View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DanP Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jan 2018 at 7:40pm
Fantastic fix and massively useful discovery on those error codes referring to component locations!   This is going to definatley be useful to someone in the future.   Kudos!

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