Failed BIT 4a

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Failed BIT 4a

Postby smithb » January 5th, 2019, 12:04 am

I'm picking up an old project and need some help. I have a 4220 that fails BIT 4a. The SPOT button stays lit throughout the whole test no matter which wheel is dropped. The problem is that each of the wheel drop switches tests good with an ohm meter. Any ideas what my next step should be?
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Re: Failed BIT 4a

Postby vic7767 » January 5th, 2019, 12:34 am

Where are you testing continuity from? Do you disconnect the 2 wire connector from the board and test at the connector, or the micro-switch?
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Re: Failed BIT 4a

Postby smithb » January 5th, 2019, 12:45 am

I'm disconnecting the connectors and testing there.
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Re: Failed BIT 4a

Postby vic7767 » January 5th, 2019, 1:26 am

You may have a poor connector contact or a broken copper trace on the board. It may be easier to replace the board.
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Re: Failed BIT 4a

Postby smithb » January 5th, 2019, 9:45 am

I was afraid of that. I'll pull the board and check a few things, but he'll likely end up a parts donor. Thanks for your help.
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Re: Failed BIT 4a

Postby smithb » January 5th, 2019, 10:06 pm

Well... I pulled the board and everything looked super clean, so I put it back together and now it passes all tests. One of the female board connectors was acting up a bit when I first put the ohm meter on it but it showed full continuity eventually. I figure either that was the cause or someone crisscrossed connectors at some point.
It's super clean and the body screws were all mismatched so somebody has definitely had this thing apart in the past. I'm kicking myself for not checking the connectors before I pulled the board. Oh, well... It works.

Thanks, again!
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