Intel MDS-II Model 230 Development System Restoration

10/9/21

We disassembled the system to inspect it and to take pictures of everything.

We disconnected the DC outputs that connect the power supply to the Multibus backplane and to the I/O controller board on the back of the chassis. We plugged the AC power cord into a Variac, set the Variac for a low voltage output, and turned on the power. Unfortunately nothing happened. We are in the process of determining why the AC power isn't getting to the fans and power supply.

With the Variac set to 30 VAC output we see 30 VAC on the internal floppy power cable. That should mean that the power cord, fuse, voltage selection switch, and power switch are all OK. We checked the resistance of the thermal cutout. It was just a few ohms, so that is OK.

We reassembled the chassis, reconnected all of the internal DC power cables, and powered up the system with 30 VAC input. This time the fans started running slowly, so there was AC power to the power supply. We slowly increased the AC voltage and the DC voltages to the backplane all look OK.

We plugged all of the boards into the chassis and powered it up. The LEDs for switches 0, 1, and 2 and RUN lit. Nothing was displayed on the CRT. We fiddled with the brightness control and could sometimes see a pattern on the CRT while the control was moved.

We set the LOCAL/LINE/DIAGNOSTIC switch on the back to diagnostic, and after a few minutes the CRT displayed INTELLEC SERIES II IOC DIAGNOSTIC V1.1. We ran the GENERAL and KEYBOARD/CRT diagnostics and the passed. We did not run the DISK diagnostics because this system does not have an internal floppy diskette drive.

With the LOCAL/LINE/DIAGNOSTIC switch set to LOCAL everything we type on the keyboard is displayed on the CRT.

With the LOCAL/LINE/DIAGNOSTIC switch set to LINE and reset the system. The CRT displayed SERIES II MONITOR, V1.2 and a prompt. We tried a few commands and it looks like it is working.

10/13/21

We connected the diskette chassis from the MDS-800 to the MDS-II, put a CP/M diskette in drive 0, and pushed the reset button. It cleared the screen and displayed the monitor prompt on the CRT. We tried ISIS V3.4 and ISIS 4.1 and got the same results. Maybe the boot sequence for the MDS-II is different from the MDS-800? Time to read the manuals.

The MDS Monitor doesn't display on the CRT anymore. We removed all of the boards but the IPB, and still no monitor prompt. We reseated all of the chips on the IPB and no change. Maybe the IPB CPU board (most likely) or the IOC I/O Controller board (less likely) is not working correctly.

The power supply voltages to the Multibus chassis are all OK.

So that means that the CRT, Keyboard, IOC, CPU board, and RAM board are all working.

Next time we will power up the diskette chassis. If that works we will connect it to the MDS-II chassis with a floppy cable borrowed from the MDS-800 and try to boot ISIS and CP/M from diskette. We still need to test the serial ports, connect the printer and see if that works, make a cable for the paper tape reader and see if that works. The last project will be to removed the math board, install the ICE-85 boards, connect the pod to an MCS-85 and see if we can do hardware debugging. We also need to get the interface cables from the donor.