Re: [N8VEM-S100:6214] Re: 80386 CPU Board

Thanks David for your "eagle eyes", unfortunately correcting the .1uf -->47pf didn't fix my issue. I've also swapped every IC except the 386, checked every resistor and resoldered very joint.

Slowing the system way down (2mhz oscillator) makes it switch back and forth properly.

I've tried swapping the 74LS74's for 74F74's without any effect. Unfortunately I lack the expertise or equipment to see what's really going on.

Using QIED swaps back and forth perfectly, but once the QOEE,01 is used the system won't reset to Z80 mode using either QIED or QOEE,00 and the LED's stay fixed at the TMA0 setting.

I'll try Johns suggestion this weekend and see if it works.

Once more curiosity is that when I boot MSDOS the TMA3 led comes on. If I've activated the 80386 by QOEE,01 booting MSDOS will switch to TMA3 and drop back to the Z80, but if I've activated the 80386 with QIED it boots fine.

On Friday, February 6, 2015 at 12:39:37 PM UTC-5, monahanz wrote:

From: n8ve...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of John Monahan
Sent: Friday, February 6, 2015 9:00 AM
To: n8ve...@googlegroups.com
Subject: RE: [N8VEM-S100:6214] Re: 80386 CPU Board

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 in 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 RAISE 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: n8ve...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of David Fry
Sent: Friday, February 6, 2015 12:13 AM
To: n8ve...@googlegroups.com
Subject: Re: [N8VEM-S100:6212] Re: 80386 CPU Board

Hi Gary,

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 :-)
best regards

David Fry

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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Re: [N8VEM-S100:6214] Re: 80386 CPU Board - Correction