At 20:58 -0500 5/3/13, Blair Aakre wrote, and I snipped: >Q1 and Q2 are part of the oscillator circuit. They are both identical 2N4258 >PNP transistors according to my CPU board schematic. > >-Blair >
An oscillator! In the picture of the board there is a Y1 identifier. That would be for a crystal for frequency control. It's possible that it's bent over to the left as in the picture but it might also be missing. Transistor substitutions will be easier to select with the frequency of the crystal available. It's usually printed on the crystal. I also see L1 which is an inductor. Oscillators are sometimes fussy about details: like an inductor to compensate for the input capacitance at the base. I doubt that there is any difference between 2N4258 and MPS4258 the change likely occurred when the Motorola part found use in a military system. -- 1801 - Joseph Marie Jacquard uses punch cards to instruct a loom to weave "hello, world" into a tapestry. -- -- ----- You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups "Vintage Macs" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
