Good point Dave, C67/R18 is to pull out noise/false triggering from pHLDA transferring control to the slave. (came from an old Godbout board, if I remember correctly). Could be an issue getting back to Z80.
One test you could do is use a completely separate port in your system to flip between CPU’s…
Find a board that has a port I which you can output a bit high or low. Our Parallel Port I/I board is ideal for this. It must be high on reset. We need a spare OC gate. Use U49 pins 11 & 10 on the 80386 board. Disconnect the K4 jumper on the SMB V2 and all jumpers on P36. First check the “O” command then does nothing. Next run wire jumper from a bit on your (new) output port to the bent out pin of U40 pin 11 . Connect the bent out pin 10 of U40 to pin 2 of P36. Also jumper P36 3-4. Lower the bit on your new output port, the Z80 should switch out and the 80386 in. With a logic probe check the levels of pins 11 & 10 of U40.
Next within the 80386 lower the bit. The Z80 should switch back in. Again with a logic probe check the levels of pins 11 & 10 of U40.
Report back!
John
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of David Fry
Sent: Friday, February 6, 2015 12:13 AM
To: n8vem...@googlegroups.com
Subject: Re: [N8VEM-S100:6212] Re: 80386 CPU Board
I compared your picture to my board and jumpers are the same BUT one thing I did notice,
Check C67 directly beneath the 80386 chip, have you mistakenly fitted a 0.1UF here as it looks the same type as the cap next to it (C18 which is a 0.1uf)
C67 should be a 47pf and is in the master/slave area of the circuitry.
I only noticed it because on my board the 47pf is blue and the 0.1 next to it is yellow :-)
On Friday, February 6, 2015 at 4:42:55 AM UTC, Gary Kaufman wrote:
John -
Thanks, that helps narrow things down!
- Gary
On 2/5/2015 10:53 PM, John Monahan wrote:
Jumper looks exactly as I have Gary.
John
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