I have a Mac Plus that I bought new that I am trying to get
operational again.  When it finally became unusable, the screen would
go to a thin vertical line and sometimes it would work again if I
tapped the case.  This issue would happen right away upon turning the
Plus on.  I resoldered some of the joints (L2, C1, J1) on the analog
board and it seems to be better, but there is no start-up bong when I
turn on the machine.  The screen appears normal with the flashing
floppy icon.  I haven't been able to do enough testing yet to see if
the resoldering has fixed the issue after it has been warmed up for a
while.  What is the cause of no start-up bong?

The flaky joints you particularly need to check are the ones associated with the 4-pin 
connector that goes between the analog board and the "yoke" around the crt's 
neck. Resolder (with fresh solder) the connections on the analog board. Then, undo the 
connector and inspect the pins in both halves. In some cases these get damaged from the 
heat produced by the flaky contact. Repair or replace as necessary.

As to the "no bong" problem, double-check the speaker, the capacitor in series 
with it (you'll have to do a little tracing), and the connections associated with them.

And as to your other question about the "micro screen" logic board, doublecheck 
your ram. Make sure that the ram is good, installed properly, and that the ram size 
resistor is configured correctly for whatever ram capacity you've got.

For other details, there are some troubleshooting hints, along with a schematic 
of the Plus analog board here: 


Prof. Thomas H. Lee
Center for Integrated Systems, CIS-205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
650-725-3709 voice, -3383 fax

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