I think, with a working RAM board and an empty one, it would be possible to make a piggyback adapter that allowed you to copy the contents of the good one to the bad one, no PC necessary.
Interested to know if there's a schematic of the board or at least a parts list (mainly just to know what the transistor is, I suspect a jellybean NPN type but...)
Would be a fun project to use something like a PIC or Arduino to replace the entire board, I think it would be easy enough to find a chip with enough NV storage that it could be a one chip solution.The idea of replacing the logic board with a modern microcontroller has crossed my mind
You could also replace the matrix board, which not only is in a bad place on the radio but overly complicates the process of reading switches off the front panel.
Remote control could be added.
I do like the idea of cloning a known good Ram board...
Cloning looks like it might be very simple, just jumper the data and address lines between boards, assert WR on the board to be written to and count through the address space with a simple binary counter
The problem is 18 year old software with no sourcecode that bit-bangs the printer port to drive a 26 year old hardware interface design.
However, if you don't need to access the hardware interface it works OK under Windows NTVDM, and can be used to load, save and edit its .BIN files, which is sufficient to figure out the file format. A very quick look indicates the file may be a simple sequence of 16 bit values, stored in low byte first order, of which the upper three nibbles of each are zero and the low nibble is the contents of that memory module location.
The easy way forward would be to use an Arduino for the memory module interface, and create and publish a sketch that can read and write ICOM memory modules, and transfer data to/from a PC, preferably in a human readable format e.g. ASCII hex dump or IntelHEX, so it can be driven from any terminal program and isn't tied to an OS or even to a particular interface between the PC and the Arduino or similar board. An Arduino UNO should easily be capable of powering the memory module and controlling all its pins with no added hardware other than jumper wires. The sketch should document the interconnections, and also use pin names rather than absolute numbers so it can easily be ported to future generations of the Arduino platform. I believe an Arduino-based interface, with open source firmware will be highly future-proof, as Arduino-like boards are likely to be the de-facto standard for many years to come.
Ideally someone with a fully working rig, + a spare memory module that has already lost its contents would volunteer to do the development, as that would be minimum risk as they could test with the blank module and the BIN images to be found on the web, and confirm normal operation before risking their good module. Otherwise, with a good reverse engineered schematic, + a N.O.S. RAM chip, it should be possible to build a functional clone of the memory board with a little effort.
You'll also need to write a utility to convert the existing .BIN module dump files to your chosen human readable file format.
The uPD444C 1024 x4 bit SRAM datasheet can be found at http://www.pisi.com.pl/piotr433/manuals/upd444.pdf
The rest of the info needed can be found in this thread, though it would be nice to actually ID that transistor, and get the value of the vertical resistor next to it, or to have a schematic of the RAM board to work from.
No, an Arduino or other MCU would *NOT* be a good choice for a replacement for the memory board. Responding to an address pin change fast enough is likely to be difficult and adding an extra source of digital noise to a sensitive radio receiver is seldom a good idea.
While it may be worth considering a FRAM based replacement board, unless you need the extra memories that are provided by the commercial board that has been discussed earlier, surely the easy option is simply to fit a battery holder (which will be a bit of a bodge job - Epoxy putty or 3M VHB tape + patch wire), which will get another 10 years out of these rigs before you have to revisit the problem. Either way, you'll need some sort of programmer
So could you make some measurements, if you could capture a read and a write sequence so we can get some kind of idea how fast they are?
Also would be interesting to see a capture of the control signals in relation to the data and address lines.
Plus, the number off that transistor?
The interesting thing in there is the bit that says the programming information is available from Icom and that users with a PC can experiment.
Which to me would suggest there's a way to load these in the radio...
Would be very interested to see more documentation.
They did make an Interface Unit EX309 for the radios. i have one installed in mine. Never used it. Don't recall ever seeing any instructions on commands/control possible. It just came with a single page with some pinout info and installation instructions.
It might be interesting if someone could find more of those Tech Talk notes. So far nothing much on ICOM sites, some more recent ones but nothing old. Maybe time to check the WAYBACK Machine.
Silveruser,
that is great information. at this point we can use anything that is available for further testing. Thanks for sharing that.
I also agree that Icom may had that in mind after reading that article. If they ever let this information out is beyond me. I have contacted Icom in the past for information on old radios and all I got then was "Sorry, we no longer support that". So unless we find a tech from the 80's that used to work for them I am pretty sure this information is mute. Hence why I started this thread here and started some videos on the 745. I think I will also start hunting for "parts and donor" rigs to help with some of the experiments. I do own a rig in good working order that appears to have the original battery in it. From that article the battery is only needed when the unit is not being used.
I just got home from work, went out to the shop and it is a chilling 38 degrees in there. Will take an hour or so the heat up then I will spend a bit of time tonight looking things over. Really need to get the house lab back together now.
I do have a EX-314 board in hand. That transistor (Q1) is a C945. Like you said cJay just a jellybean part.
D1,D2,and D3 looks to be 1N914.
C1 the big green ceramic is a 104M (0.1)
C2 is a 47 (47pf)
R1 47k
R2 390
R3 10k
R4 4.7k
R5 1.0k
R6 47k
W1 - W8 1 ohm
W9 jumper
IC1 HD7432P
IC2 D444C
TR1 C945
Well that EX-309 seems to be an interface to the CT-10 which is capable of being interfaced to an RS-232 capable computer or terminal.
It's a bit of a mire of equipment.
I think tracing the EX-309 connections in the IC-751 logic board schematic, J10 and J15, might be interesting but we're diverging from the original subject now, I don't think it's of much use unless we get the CT-10 and whatever software Icom made available for that combo.
It's late here, I'm up again at 05:00 and it's almost 22:30 now so more digging tomorrow.
I reckon the parts list for the larger chip board will be exactly the same except for the D444 being swapped for a D446?
As soon as the ram board is removed the display goes all "0"