On Fri, Feb 7, 2025 at 5:08 PM William Sudbrink via cctalk <[email protected]> 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
