[sebhc] IC information

[Lee Hart]

Glyn Firth wrote:
> 
> Lee,
>      I do not have the schematic, would you please advise.

Glad to! The silkscreen on the PC board labels IC203 pins 1, 2, 3, and
4. Pin 1=ground, pin 2=reference, pin 3=output, and pin 4=input.

Remove the dead chip, and get a 7905. I'll assume you have one in the
T0-220 package (3 leads, plus a metal heatsink tab). Let's number the
pins of the T0-220 package. Lay it on the table, with the metal tab on
the surface on the table and the 3 leads pointing toward you. Pin
1=ground=left pin, pin 2=center=input, pin 3=right=output.

So, install the 7905 in place of the 79MGT2 as follows:

7905	79MGT2	function
----	------	--------
pin 1	pin 1	ground
pin 2	pin 4	input (-18v)
pin 3	pin 3	output (-5v)
	pin 2	reference (no connection with 7905)

You can unplug the 8080 (IC213) and ROM (IC204) to test that the -5v
supply is fixed and working; this will prevent possible damage to the
chips if you get it wired wrong.
--
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Lee A. Hart  814 8th Ave N  Sartell MN 56377  leeahart_at_earthlink.net

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