deramp5113
Veteran Member
From what I can see looking at the jumpers on your PROM/RAM card and the CPU board, the system is configured as a very standard VG system. During the first three bus cycles after power on or reset, the PROM/RAM board responds with the first three bytes starting at E000h (in the monitor PROM). These first three bytes are a jump to the initialization routine in the monitor PROM. The init routine initializes the video display and then puts up the command prompt. The monitor only requires the 1K RAM that is on the PROM/RAM board for operation.
The PROM/RAM board can’t force a jump to the boot PROM on the Micropolis FDC (at F800h)
Now that you’ve checked the power supplies on each board, let’s look at other simple possibilities.
1) The CPU is not reset/running properly. An ECO in the manual for the CPU board suggests putting the axial 22uf cap back in the reset circuit (just to the left of the CPU - you can see it has been removed on your board).
2) I assume you’ve tried pushing the reset button on the back as well as simply cycling power?
3) The PROM/RAM board or the EPROMs or RAM chips on the board have a problem. Carefully remove and re-insert the EPROMs and the two RAM chips a few times to freshen up the contact between the pins and sockets.
If none of these tests reveal anything, do you have an oscilloscope?
Mike
The PROM/RAM board can’t force a jump to the boot PROM on the Micropolis FDC (at F800h)
Now that you’ve checked the power supplies on each board, let’s look at other simple possibilities.
1) The CPU is not reset/running properly. An ECO in the manual for the CPU board suggests putting the axial 22uf cap back in the reset circuit (just to the left of the CPU - you can see it has been removed on your board).
2) I assume you’ve tried pushing the reset button on the back as well as simply cycling power?
3) The PROM/RAM board or the EPROMs or RAM chips on the board have a problem. Carefully remove and re-insert the EPROMs and the two RAM chips a few times to freshen up the contact between the pins and sockets.
If none of these tests reveal anything, do you have an oscilloscope?
Mike
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