Trying to upgrade the ROM sockets

I began to had connextions issue with my ROM sockets lately, this issue seem to be cause by the fact that I have to pull out the ROM chip all the time for programming and that cause the sockets to become loose with time. I ordered a pair of 32 pins ZIF sockets but after recieving it I realized that the board hole where not big enough for the ZIF socket pins..

My solution was the enlarge the hole with a small metal pic I had, at first everyhing seem to have worked great :

Mistakes where made..

But after testing, I realized that some address and data lines where not working anymore. After doing some contuinity test with my multimeter I concluded that I had broken some pads connection. After two days trying to fix my mistake I was still having random issues.

Bite the bullet

So I decided the bite the bullet and rebuild a new board from my spare PCB I had. I need to make sure that I remember all traces that need to be cut and to connect all the bodge wire from the “old” board. In the meanwile I soldered some headers instead of the ROM sockets and I constructed two little boards with 40 pins ZIF sockets then put a pair of 90 degres pins on the botom to be able the stack them on top of the header. That way theses ZIF board can be unplug and replace by normal sockets when no longer neede and they can be use on any 40 pins DIP chip in future projects :

Here’s a close-up shot off the botom of the ZIF boards, the 90 degres pins has been soldered like if there where SMD components. This gave them a little offset on the right or left of the original socket thus giving some clearance for some board design where ZIF sockets where not planned to be use :

Everything seem to be fitting well with the headers on the “new” motherboard :

The nexts steps are to reproduce all the modifications that I made on the last motherboard and begin the testing, after that I will be able to continue where I was before broking the last board.

Future plans

I had started to work on the next motherboard revision to fix the issues with the current version and add more flexibility. Here’s where I’m going for :

• The first thing I decided to do is to have a MATX form factor to be able to put my computer in a case.
• Put the CPU, the CO-Processor and lines transcievers on a daughter card.
• Replace the 80284 Clock Driver chip by a GAL20v8b.
• Adding a ATX power supply connector and front case panel header for power and reset switches.
• Onboard IDE support to be able to use a compact flash.
• Header spot to add a CH376S module for USB drive support.
• VT82C42V PS/2 keyboard controller.
• DS1232 chip to control power on reset and watchdog reset in case of crash.
• More SPI devices like a Real Time Clock, SD Card, 7-segments display and mabey a small EEPROM to save some settings.
• DMA controller socket for the future.