Why logic board chimes when pin is touched with probe?

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Macbook pro 2008 Logic board 820-2330A

Roger @roger36774

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发帖于: 2016年9月13日

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Why logic board chimes when pin is touched with probe?

Hello Guys,

Maybe one of you can help with this unusually weird problem I have with my 820-2330 logic board. The board powers on, but won't chime or boot until I touch a couple of specific pins on chip U8900. This is what happens exactly; when the board is powered on and I touch pins VO or OCSET on U8900 the board then chimes and boots normally. It is driving me crazy trying to figure this one out. At first I replaced U8900, then I replaced both FETS, then I replaced the Critical caps after the inductor all to no avail. Any help would be appreciated.

Thanks,

Roger

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Paul Bade @paulbade 声誉积分: 1 1 · Answer 1 · 2019-01-10T13:41:28-07:00

Paul Bade @paulbade

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发帖于: 2019年1月10日

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Look for an open trace or bad component attached to one or both of the pins you mentioned. If an input pin is not connected, touching it with a logic or scope probe connects it to ground through the probe circuit, thereby giving it a logic low (“0”)signal.

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Macbook pro 2008 Logic board 820-2330A

Why logic board chimes when pin is touched with probe?

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