If M28 pin 13 has 2.13V, then I think that is enough to turn on T20. Which is why the power supply is "off".
So what I think this says is * When you turn on the power switch (mem switch also on) the power supply tries to start * something triggers the PCS signal or the /RESET signal to clock M28 flip flop * the flip flop output at pin 13 turns on T28 , causing shut down. On Mon, Oct 19, 2020 at 9:15 AM Charles Hudson <[email protected]> wrote: > > > ---------- Forwarded message --------- > From: Charles Hudson <[email protected]> > Date: Mon, Oct 19, 2020 at 9:08 AM > Subject: Model 100 Boot Issue? > To: <[email protected]> > > > Stephen, > > Thank you again for your responses. You pointed to M28 (an MN4013B > flip-flop on my board) as an indicator of a shutdown signal. I tested M27 > (an MN4011B 4-output NAND) and M28. Neither has positive voltage at pin > 14, and M28's pin 13 actually measures a few tenths less than 0VDC. > > The choke and ferrite in the leads from the jack are OK; 8.06 VDC arrives > at the board and approximately this much makes it to the power switch. I > checked the reset switch to see if it was shorted but it does not appear to > be so. > > This may take me forever but at least it keeps my mind off my poison ivy > rash. > > Thanks again, > > -CH- > > Afternote: The zero voltage on M27 and M28 occurs when the memory backup > battery switch is "off". If I repeat the measurement with it "on" I get > 2.13 VDC or so, whihc I have assumed is the contribution of the memory > backup battery. > > Rule #1: Don't assume? >
