Re: -5V on IIgs

[et472@FreeNet.Carleton.CA (Michael Black)]

"James Littlejohn" (narguthru@yahoo.com) writes:
> On Mar 4, 12:25 am, e...@FreeNet.Carleton.CA (Michael Black) wrote:
>> "David Wilson" (mcs6...@gmail.com) writes:
>> > On Mar 4, 4:08 pm, "James Littlejohn" <nargut...@yahoo.com> wrote:
>> >> I have been going over the schematics of the IIgs, and was wondering
>> >> if the -5v line goes to any thing besides the RGB output chip? I can
>> >> not find anywhere else where it is used. Will the computer run without
>> >> this feed?
>>
>> > You missed a couple of places. Page 4 UB15 and UB16 (serial output
>> > driver chips), Page 7 pin 34 of slots 1-7, Page 8 UL14 pin 11 (sound
>> > chip).
>>
>> > I would not recommend it.
>>
>> On the other hand, for a long time any drain on a minus voltage in a computer
>> has generally been very low.  So you need it, but not very much of it.
>>
>> LIkely a string of AA's would do fine, or if one wants to get fancy,
>> a dc to dc converter to convert the +12 or +5 volt line to -5v.
>>
>>    Michael
> 
> Michael,
> You would not hapen to have a schematic for a dc-dc converter for the
> -5v, would you?
> 
This is silly, I've made the same mistake in the past.

The obvious solution is to  get a tiny transformer, and build a small
-5v supply.  It's as simple a solution as anything.  I can't imagine
the -5v line is using much current, though it would be helpful to know
how much.  Pull a small transformer out of some clock radio or something,
add a rectifier and filter capacitor and then a small 5v regulator and
you've got it.

  Michael