7 Feb
2025
7 Feb
'25
9:40 a.m.
On Fri, Feb 7, 2025 at 5:08 PM William Sudbrink via cctalk
<cctalk(a)classiccmp.org> wrote:
I'm repairing/restoring a later model MITS 8 inch floppy drive. I can not
seem to find schematics for it. It is
the same as Bill Degnan has here:
https://vintagecomputer.net/MITS/88-DCDD/
You can see in his photos (and mine match) that the _plus_ 24 volt DC supply
on the board uses a 7924 (note the
9. negative) voltage regulator, with a small heat sink, directly on the
circuit board. Along with a couple of 7805s,
there is a .Motorola 2n6045 screwed to the large black heat sink. All three
of the devices drop into sockets on the
circuit board to allow the heat sink to be easily installed/removed. On my
unit, the socket for the 2n6045 was burnt
to a crisp. I have replace the socket, the 2n6045, the 7924 and the
electrolytic caps. When I test the +24 volt rail
with a dummy load, it measures +41 volts.
Page 137 of the MITS manual on that site gives the schematic of a
power supply using a 7824 and a PNP darlington power transitor (to
inclrease the availabl output current). It runs off a floating supply
from the transormer T1.
My guess is that using the 7924 in a similar circuit allows the
circuit to be turned upside-down and use a more common NPN darlington
transistor.
Is that what you have?
Is the common pin of the regultor firmly connected to the +24 output
rail? If not the output wlll go sky-hgh.
-tony