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4420 boom
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Posted 8/5/2022 06:52 (#9781311 - in reply to #9781220)
Subject: RE: 4420 boom

Southern Illinois

The magnetic switches and the neutral position on the hydro lever, not the potentiometers, are used to power the boom fold and rear centering cylinders on 4420 machines. Its a pretty simple electrical circuit so perhaps there is a broken wire in the boom harness. Likely near either the upper or lower boom arm pivots. Wiggling the harness with the hydro out of neutral and park brake set to disable the hydrostat, may cause the cylinders to pressurize. 

When not in neutral, power is sent to the magnetic switches. When they are triggered power goes to the left or right innerboom fold solenoid. This pressurizes both the front, folding cylinder and the rear, centering cylinder to pressure against each other. In the field this is what keeps the boom centered and stable. There is a flat metal "cam" welded to the upper boom pivot that must be just close enough to the magnetc switch to trigger it.

Edited by JHEnt 8/5/2022 06:54

(4420 boom center sensor (full).jpg)

Attachments 4420 boom center sensor (full).jpg (16KB - 17 downloads)
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