To round up so far..
@PaulJ https://www.exxosforum.co.uk/forum/viewt ... =70#p29868 Looking like ACK isn't pulsing.
@Icky has tried jumpering the buffers and made no odds.
I think all 3 of us have checked the H4 schematic and found nothing wrong.
The only changes I made or know of are:
I think we need more peoples builds up and running to test the DMA port as there shouldn't be anything wrong anywhere.Other than, as Icky said, I used a NOR as a inverter for the MFP input, swapped a LS04 for a LS06 (hence the pull up on HDRQ). I also renamed FDINT to HDINT, but all points look connected the same as the Alpha.
Aside from the buffers (the DMA buffer was tested on a bodge board and literally copy-pasted over) even so, Icky says it still not working jumpered.
The only thing I can think of is if the propagation delays of the chips I swapped about are the issue.. But there isn't any real different anyway. Both swaps are still inverters, so no logic function changes.
Been around it all again, still don't see anything wrong. compared it to the Alpha and STF diagram, unless I am going blind, just nothing wrong circuit wise that I can see.
The only other difference is the case of the DB19 isn't grounded on the H4 ? I don't have a board here to check.
I probably won't get my boards until after xmas, so won't be able to look into it myself
I think it would help if someone checks on a scope that all the DMA lines before and after the inverters etc are all looking as expected.
So we have these as potential causes:
- Bad soldering - Which 2 people would have the same soldering issue
- Bad schematic - which 3 or 4 people have checked and found nothing amiss
- Everyone's forgot to plug power into ultrasatan.
- Aliens.