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From: steveh@tasman.cc.utas.edu.au (Steven Howell)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Odd monitor problem
Message-ID: <steveh.671508013@tasman>
Date: 13 Apr 91 02:00:13 GMT
References: <1912@hpwala.wal.hp.com>
Sender: news@diemen.utas.edu.au
Lines: 35




	Assuming its a mac plus, then the chances are you have simply a dry 
joint. ie a bad solder connection between component and the copper circuit board

	This is a common failure point to the macintosh (128,512,plus) and
simply repaired by removing the old solder and applying new solder to the joint.

	For the screen to go out, but the mac still operates as normal, even
though you cant see it, points to several locations of the power/sweep board.

Very Commonly, and usually is J1. This connection has a tendancy of failing
on the horizontal outputs (The two connections on J1 closest to the top of the
board) due to high current oscillating voltages. You may have to peel up the
insulation support adhesive pad to get to it.

Along the same lines is C1. It can develop bad joints around its two leads,
same goes for the in series L2, and unusually L3. all located at the top of 
the board.

Also prone to bad joints are T1 J2 and commomly also J4. The information
comming into the sweep board from the logic is oscillating at approx 22KHz.
This causes the the Horizontal, Vertical and Video joints on J4 to fail.


Try these first. the majority of faults related to video are usually within
this area. This of course is assuming that a component has NOT failed, but
basically has a dry joint, which i suspect.


See How You Go ay'.


Steve h