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Russell H.
Russell H., Service Tech
Category: Marine Electronics
Satisfied Customers: 10910
Experience:  8+ years of professional experience
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How are you have received the 789ci HD into my work shop and

Customer Question

Hi how are you
have received the 789ci HD into my work shop and it has had moisture get inside of it. At the moment it has only affected the part of the circuit directly below the Power connector (P100)
There was a lot of corrosion at Q101 and between Q101 and D102 but not affecting D102
My question is: Between D101 & D102 there is an area for 4 components there are 2 x components (unmarked). was there 4 and did the corrosion eat the other 2
That is it
Hopefully you can help
Submitted: 1 year ago.
Category: Marine Electronics
Expert:  Russell H. replied 1 year ago.

Hi, thank you for contacting My name is Russell. I will do my best to provide the right answer to your question.

Corrosion might 'eat' a very small component like an SMD component (surface-mount type), but if so, you would see *some* sign of their presence or former presence. For instance, a trifle of eating-through of the holes in the circuit boards in which they were mounted, might show up, if the leads got eaten away as well as the components themselves.

Or you should see the remains of the leads sticking out of the circuit board. Or at least, see the remains of the leads of the missing components sticking through to the other side of the board. Such evidences would be indicative of the former presence of a mounted component soldered into place.

But there might well be blank/unused space on a circuit board. Some revisions of the same board do not have some components; or some revisions of the board might have had the presence of those components edited out 'at the last minute' as it were, after the boards and their layout had already been completed.

(A photo or picture, of both sides of the board in that area, might indicate something more to me about the question.)

Customer: replied 1 year ago.
Thank you Russel for your response I respectfully ***** ***** are at the very same place here in our understanding of this situation. I actually need someone who can look at the Schematic or has worked on this particular systemI have cleaned it all up and there may be evidence of maybe 2 SMD's that was there or it may just be a jumper or the board it could just be the board has been damaged by the corrosion ................. if it is a fact that there are missing components what are they.
I can tell you that the damage is limited to that area aloneI'm glad I could attach some pics it makes my explanation clearer for youAgain thank you very much
Expert:  Russell H. replied 1 year ago.

I admit I don't have schematics. But I suspect from the look of that board, that there were components there, quite possibly - simply because the two components that definitely are there, bridge from one broad circuit run to the next run adjacent, apparently - and the place for those two (missing) components straddles similarly, from one board circuit run to the next.

If those three runs connect to a two-winding or center-tapped transformer, then I would suspect it as all the more likely.

But I do not have hands-on experience to call on with this model, nor do I have a schematic. So I offer to Opt Out and open the case to any other Expert here who does.

Customer: replied 1 year ago.
I do thank you for your time with this. I am hoping for the info from the Schematic or someone who has worked on one of these units. But I can tell you are a processional in your explanationsThank you
Expert:  Russell H. replied 1 year ago.

Thanks. - Before I Opt Out and turn this over to another Expert here, I want to know: can you post a picture of the reverse side of that area of the circuit board? for me, or the next Expert, that might be quite helpful.

Customer: replied 1 year ago.
Hi Russell
Sorry cant do. But there are no parts in that area that go through the board at all so would not shed any light on the situation
But thanks for your time anyway
Expert:  Russell H. replied 1 year ago.

OK. Sorry I couldn't provide more help.

I have Opted Out, with apologies.

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