Ithica IA-1010 rev 1.3 2716 mod and enhancement

After the success of getting our Poly-88 up and running I wanted to clean up some hacks and simplify things. One of those hacks was to replace the 2708 monitor ROM with a stack of sockets bodge wired together in such a way to adapt a 2716 to the pinout on the board. After reading in the manual that there are instructions for converting the board to use a 2716 I wanted to do that so the card sits flatter in the card cage. This will explain how to make just the switch to the 2716 without increasing the monitor ROM size (power and chip select lines), how to expand the monitor ROM (and make it switchable), and how to quickly enable and disable the ROM entirely.

That’s the instructions for swapping the 2708 for a 2716. I notice a few things right away that I knew would be there, like the different power supplies and an enable line. I also notice something mucking with A10 (the highest address available on a 2716 and not available at all on a 2708. That tells me that this mod will map the entirety of the 2716 into memory and we will lose that 0x400 worth of RAM that we had on the other side of the monitor ROM. Initially this was not what I wanted, but I decided that I would like to make this switchable and I think I know how to do it.

In the instructions above it says to cut IC23’s connection to A10 and ground it. The trace for that is on the top of the board so I pulled the socket and cut the trace. I will make it switchable in a bit, but the instructions are not clear where A10 actually goes on this board. Looking at another line in those instructions you can see we’re supposed to attach IC25 pin 11 to one of the 2716 pins, I verified that this used to be connected to IC23’s pin 12. It seems that the 2708 -> 2716 size mapping increase is caused by these two things. I just need to be able to pick between grounding A10 on the 2716 while tying the board’s A10 line to IC23, and tying the board’s A10 line to the 2716 (IC36) while grounding IC23’s pin. I chose a 5 pin header and two jumpers to accomplish this. The pinout goes GND-IC23-IC25-IC36-GND and by moving two jumpers I can swap the size of the monitor ROM this board recognizes. I also cannot connect both IC23 and IC36 to IC25 simultaneously because the jumpers share that physical pin.

I went with right angle header because I knew I wanted low profile, I didn’t want wires or headers sticking outside of the card edges, and I had them handy. You also see a three pin header hooked to a different breakout that used to hold a wire link jumper. I did this so I could remove the monitor ROM entirely if I wanted. Look:

This section says that for using the monitor ROM you connect J and H, but if you don’t need it connect J and K. That’s fine and all, but look at the top. Revision 2 of the board had the benefit of being laid out so I could put pin headers and use shorting bars to quickly jump between configurations. This is an earlier revision so I don’t get that nicety. Now I have it.

vias used as pass through holes, no electrical contact is made

Here you can see all my yellow wires for this mod. You can also see one lone black wire connecting ground to an unused pin on the front panel header that allows me to power the LEDs I used on my bargraph substitute for a front panel. You can also see some red wires that were installed before I got the board. I assume that’s to fix compatibility with the expandoram or something but I didn’t like how they were done soldering directly to chips. I understand that the board cuts I made (you can see some in this picture) are permanent changes to the traces on the board and are not as easily undone as desoldering from chip legs, but I don’t think anyone will need to put this back to using a 2708. Having a programmer that can burn 2708 chips is odd enough these days, but if you do have some chips to flash I think you would want to install them into a board that you really don’t want to cut up (for historical reasons). 2716 equivalent EEPROM chips are also super convenient so you don’t have to cook them for every change. I also find that the chips will need replacing more often than the board will need rewiring, so swapability is important.

2 Responses to “Ithica IA-1010 rev 1.3 2716 mod and enhancement”

  1. wilkinssscreamer Says:

    great blog!

    Im trying to learn about electronics now and have a few questions-

    1.I also got a chinesium tester with broken screen- how do you solder wires to pcb with the connections being so close together?

    2.how to recognise eeprom chip?

    3.know any good resources to learn electronics,repairs,hacking,etc.

    thanks,from County Down,N.Ireland.

    • abzman2000 Says:

      It’s a good thing to get into.

      1. I got a soldering iron with variable temperature and a selection of different size tips. Things get much, much easier if you get better tools and I can recommend from personal experience the Weller WES51 soldering station (I’ve had it a long time and it’s worked well for me), some good Multicore brand leaded 60/40 solder with flux inside, liquid flux to help make solder stick to places it should and not stick to places it shouldn’t (https://store.rossmanngroup.com/amtech-nc-559-v2-30-cc-16160.html) and some good solder wick (https://www.chemtronics.com/soder-wick-rosin-2). I also recently started using a Hakko FR-301 desoldering gun and chip quick for desoldering tricky parts.

      All of those are optional and you can substitute for any or all of them by just swearing more, breaking more things, and/or taking longer to get the job done. The more good tools you get the easier things get.

      2. I have spent literal years looking up the part numbers on chips I found while taking things apart. After a while I get to be able to recognize patterns. Prefixes like 24, 27, 28, 25, 49, 39, followed by a number like 010, 020, 040, 080, 16, 32, 64, 128, 256, 512 and possibly having a letter in the middle like C or Q would tell me it’s probably an EEPROM, a window in the top tells me it’s an EPROM. You also get to know brands like winbond that do lots of business in EEPROM chips.

      3. I usually read hackaday and google things like “arduino” plus whatever I’m working on. even if I don’t intend to use it with an arduino because people who write about arduino projects also talk about the general reverse engineering. You might also try “teardown” or “schematic” or just “hack”. I usually surf google images looking for pictures that look like they were posted by someone explaining hacks they’ve done on the thing you want to know more about. It’s pretty easy to tell the difference between the picture from an amazon listing and one on someone’s bench with hacking tools nearby, go see what their site or post has to offer.

      I also found some people that write very well that I follow even though they may not be as experienced as I am in some areas, their information is still usually informative:
      https://blondihacks.com/
      https://johan.kanflo.com/
      https://mightyohm.com/blog/
      http://blog.tynemouthsoftware.co.uk/
      https://spritesmods.com/
      http://www.neufeld.newton.ks.us/electronics/

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