rosco_m68k bus board build guide

A five-slot backplane for the rosco_m68k that also powers the whole system. Four soldering stages, then a voltage check before any card goes in. The same guide is available as a PDF.

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Tick the kit off against the packing list, then build in the order of this guide. Low parts go first, so the board always lies flat while you solder.

Which way round#

Every map shows the component side with the power section on the left and the five bus slots running left to right. Keep your board that way and "left", "right" and "up" in this guide always match what you see.

You need#

Temperature-controlled iron with a fine tip, solder 0.6–1 mm, flush cutters, small pliers, multimeter, masking tape. For repairs: flux and solder wick.

Three parts that can go in backwards#

Every joint#

The routine#

1. Heat the pad and the lead together.
2. Feed solder into the joint, not onto the tip.
3. Take the solder away, then the iron. Hold still until it sets.
4. Trim the lead just above the cone.

No chips here#

Nothing on this board is static-sensitive, but the cards you plug into it are. Never plug or unplug a card with the power on.

How#

1. None of these has polarity. Bend the leads, press the part flat on the board, solder, trim.
2. C2–C5 sit along the top edge between the slots. Seat them low: cards will stand right next to them.

How#

1. LED1: solder one lead, check the LED stands straight, then the other.
2. U1: with pliers, bend all three legs down 90° where they narrow. Lay it on the board, tab down, legs in their holes, the tab hole over the board hole. Bolt it down if you have an M3 screw and nut, then solder.
3. C1 last. Push it flat, then solder.

The regulator gets warm when it is in use. That is normal.

How#

1. J4 first. Its pins are fine: flux, a small tip, then check every gap with a magnifier.
2. J3, J2, SW1: push flat, solder one pin, check, then the rest. The jack tabs need a few seconds of heat each.
3. Headers last: tack one pin, check upright, then the rest.

How#

1. Push the header in and turn the board over onto a flat surface, so the header is held square.
2. Solder one pin at each end. Check from two sides that it stands upright. Fix it now if not.
3. Solder the rest. 400 joints: do one slot, take a break, do the next.

All 5 slots are identical, wired pin for pin.

One supply, one jumper cap#

J3 takes a centre-positive plug. On J2 the + screw is the lower one, as marked on the map. SW1, bottom left, switches the DC inputs and USB together.

First test, no cards fitted#

1. Fit the cap for your supply, connect the supply, switch SW1 on.
2. LED1 lights.
3. Multimeter on DC volts at any slot: pin 2 (top of the right-hand row) to pin 6 (third down in the same row). Expect 4.75 to 5.25 V.
4. Switch off. Now fit the main board and cards, always with the power off.

Something else happens? Switch off first.#

• LED1 stays dark: check the cap is on the row for your supply, the switch is on, and the LED's flat edge faces left.
• Voltage near 0 with 9–12 V in: regulator turned over, or the cap is not on the regulator row.
• More than 5.25 V: switch off at once. Wrong cap for the supply.
• Regulator too hot to touch: the cards draw more than it can give from that input voltage. Use a lower input voltage or a 5 V supply.

The same on every slot, seen from above with the board as on the maps: odd pins in the left row, pin 1 at the top. Signal names as on the board design.

The 2×8 header below each slot carries 16 spare lines, EXT1 to EXT16, joined slot to slot and to nothing else: cards can use them to talk to each other.

Still stuck?#

Send clear photos of both sides of the board, the supply you use and where the jumper cap sits to Telegram or solderdemon.official@gmail.com.