Berty Posted August 8, 2019 Share Posted August 8, 2019 I'm trying to locate a possible broken trace between a Z80, 8x8K SRAM and a 27C512. Am I right in thinking that a Z80 address line will run to the corresponding address lines in both the SRAM and EPROM simultaneously? Below is a diagram to explain what I am asking. Link to comment Share on other sites More sharing options...
0 Administrators Arcade King Posted August 8, 2019 Administrators Share Posted August 8, 2019 Usually there is a buffer between the cpu and rom/ram something like a 74ls244. What are you working on? Link to comment Share on other sites More sharing options...
0 Berty Posted August 8, 2019 Author Share Posted August 8, 2019 Here is a pic of the part of the circuit board. It's from the Captain Zodiac I posted a repair log on. I probed some of the other address lines and it looks like a few of them are wired like I mentioned above. Here is a pic of the chip configuration. Here is a pic with the chips out of their sockets. I am thinking that I have a break between A9 on the CPU and A9 on the SRAM. Note that I bridged A9 on the SRAM and A9 on the EPROM. I am assuming that there is a broken trace between A9 on the CPU and A9 on the SRAM due to the graphics fault I am getting... Link to comment Share on other sites More sharing options...
0 Administrators Arcade King Posted August 8, 2019 Administrators Share Posted August 8, 2019 Yeah in that configuration all the address lines should connect between the cpu and ram. Are you sure the ram is ok? what about any ribbon cables? you see those sort of vertical lines in Pinball displays with the aforementioned faults (including bad tracks) Link to comment Share on other sites More sharing options...
0 Berty Posted August 8, 2019 Author Share Posted August 8, 2019 SRAM is new. I think I lifted a track when removing the old chip. I replaced the connection between A9 on the SRAM and A9 on the 27C512 but must have lifted part of the trace where it goes to the cpu too. Link to comment Share on other sites More sharing options...
0 Holy-SNES Posted August 8, 2019 Share Posted August 8, 2019 This is where I use machine pin strips over sockets. So many boards I've repair where someone has tried to remove and solder in a socket, and so many times they go ahead and pop one in even with pads or eyelets removed thinking it will still connect. If you pull the eyelet out and go to solder a socket in, most of the time the solder won't pour through to the top side if that's where the trace is. In your case, your DMM is your best friend :) Link to comment Share on other sites More sharing options...
0 Berty Posted August 9, 2019 Author Share Posted August 9, 2019 I ended up repairing the address line as indicated in the diagram above. No change to the line in the display - that went away by itself. I even de-soldered the repair I made to see if the address line was the root of the issue. No change... I suspect that there are still some other mysteries that I am yet to uncover on this board. In the meantime... I'll update the main repair log thread soon. Link to comment Share on other sites More sharing options...
Question
Berty
I'm trying to locate a possible broken trace between a Z80, 8x8K SRAM and a 27C512. Am I right in thinking that a Z80 address line will run to the corresponding address lines in both the SRAM and EPROM simultaneously?
Below is a diagram to explain what I am asking.
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