27-11-2025, 04:37 PM
(27-11-2025, 03:41 PM)The_Huck Wrote: Thanks for the reply Ewan.
I've re-seated the top board several times to no avail.
I checked the voltage regulators on the right side of the top board and both are outputting 5V.
I removed the top board and checked the CPU had 5V and the clock. Both good.
The reset pin doesn't go high so something is holding the system in reset. Bear in mind I did these tests without the top board installed. I assume it should come out of reset even so?
I guess a faulty CPU could hold down the reset line? I may just try another CPU.
The CPU's RESETn signal is generated on the coreboard, so you will have to have the coreboard in place to check that the reset pin on the CPU is o.k.
Note that the RESET key on the keyboard does not actually drive the CPU's reset signal on a 128K (DRAM) machine. Instead, there is a Power On RESET generated on the coreboard that drives the RESET line, and the Keyboard
RESET key (with a 1 second debounce circuit) drives the NMI signal which causes the CPU to jump to location 0x66 to do a soft reset so that the contents of the DRAM are not lost due to refresh cycles stopping if a proper RESET is done.