I suggest mounting the lowest parts first (discrete resistors, speaker, axial capacitors, and diodes). Progress toward the taller parts (switches, radial capacitors, resonator, 0.3" wide ICs, etc.) Then the SIP resistors, transistor, and headers. Next, the socket strips for the 0.6" wide ICs, LEDs. Finally, install the battery holder clips.

Speaker SP1 must be mounted upside down, with the large hole on top and its pins facing away from the PCB. The sound comes out the large hole. I suggest bending the pins straight out horizontally. Then wrap a piece of scrap wire around each pin, and solder these wires into the holes on the PC board.

Be sure pin 1 of all the ICs is in the lower left corner! Be sure to observe the polarity of the diodes, transistor, and tantalum capacitor C2! The SHORT lead of LEDs D4 and D5 goes in the hole closest to the 7-segment display.

There was no room for an expansion bus connector, but you can install a wire-wrap socket for U1. Its pins on the back can plug into a "daughter" board to provide access to all the signals needed for expansion. There are two mounting holes in the top corners to mount the mini H8, or attach an expansion board.

If you want to socket the 0.3" wide ICs, socket pins are the best option (Mill-Max #0552-1-15-01-11-27-10-0, Digikey ED5037-ND, Mouser 575-055210) for the very lowest height. If you use regular IC sockets, you'll have to stack two sockets for the 0.6" wide ICs to have enough clearance.

The parts kit comes with a 27C256 32k EPROM, programmed with our latest software. Check the github site for updates. You can also use a 27C512 (64K), 39SF010 (128K), 39SF020 (256K), or 39SF040 (512K) flash ROM. Jumpers P4 and P5 must be set for the part you are using. ERROR! The silkscreened labels for P4 are reversed! Put P4 in the left position for a 32K ROM, and right position for 64K-512K ROMs.

You can use either a cheap CH340 USB adapter, or a Sparkfun FTDI adapter. The pinouts are DIFFERENT, so holes are provided for either one. Mount only ONE connector!

CH340: Use the white Molex KK connector. Cut off pin 3 (labeled 3V3 on the adapter). Bend the remaining pins at right angles (away from the 2 "ears"), and install it with its holes parallel to the PCB so the adapter will lay flat on the board. The "ears" should be on top. You can cut them off if you like.

FTDI: Remove pin 2 from right-angle header. Install it with the pins pointing right, so the adapter can lay flat against the board.

There are two holes at the extreme right edge for a wire to go over the adapter to hold it down to the board.

3-pin header P3 sets whether there is ROM (normal) or RAM at address 0. Use a jumper to short the left two pins so the ROM will be at 0. The RAM position is ONLY used AFTER you have loaded a program into the (nonvolatile) RAM. (For example, CP/M which needs to have RAM at address 0).

3-pin headers P4 and P5 should be set to configure socket U3 for size ROM you be using. If you are using a 28-pin 27C256 or 27C51, install it at U3 in the RIGHTMOST set of holes, so the left four holes are EMPTY.

Testing

Connect a 5V supply from either a USB-serial adapter, or an external 5V power supply. The pin header or Molex socket at P1 is a convenient place to connect power. The red POWER LED should light.

Turn switch S1 "ON". The board should draw about 25-30mA. If more, look for an IC in backwards of off by a pin, bad solder joints, etc.

Check the frequency at U8 pin 11 (RST7.5). It should be about 500 Hz (2 msec). The frequency is set by R2 and C5. These are low-precision parts (C5 is +/-20% and R2 is 5%) so don't expect tremendous accuracy.

Check the frequency at U1 pin 37 (CLK0). It should be exactly 2.000 MHz. This proves the resonator and 80C85 clock are working.

Every location in a blank ROM is FFh, which is the 80C85 RST7 instruction. This instruction causes the 80C85 to continuously push the program counter into the memory locations pointed to by the stack register, and jump to address 0038h (which is of course ANOTHER RST7 instruction). Thus you can use a blank ROM so the 80C85 will be exercising RAM, ROM, /WR, and /RD. Check for pulses at U1 pins 31 (/WR) and 32 (/RD), and U5 pins 5 (RAM chip select) and pin 6 (ROM chip select).

If all is well, your mini H8 can run programs!