In a previous video I covered the history of the Apple 1. The Apple 1 clone build started with the bare motherboard and the usual first problem: making sure the board itself was good before any parts went in. I checked the power rails first with a meter in continuity mode, using the large capacitor pads as easy test points for the regulated and unregulated rails. Once that looked clean, I inspected the traces and pads closely with my phone’s macro lens and found a few spots in the solder mask worth checking, but no show-stopping board faults.
From there I went ahead and populated the low-profile parts first instead of starting with sockets. I installed the resistors, using a lead-bending tool so they sat flat and evenly, and I also added the small radial electrolytics. One place I held off on was the timing network around the 74123, since that section depended on matched resistor and capacitor values that had already been tested with the chip set I was using.
With the resistors done, I soldered in all the sockets and then moved on to the ceramic capacitors, the crystal, and the transistor. One gotcha on this board was the capacitor marking: positions labeled 1.0 actually took 0.1 µF ceramics. I also added the reliability mods on the back of the board, following the known bypass capacitor layout and then checking carefully for solder bridges since the pads were packed pretty tightly together.
The power section took a little more checking than the rest of the board. I tested the voltage regulators before installation and caught my own mistake when I first measured one of the negative regulators with the pins interpreted like a positive part. Once that was sorted out, I installed the regulators, the large capacitors, and the big 5V regulator with thermal compound and its heatsink hardware. I also adapted a six-pin connector for video by trimming it down to four pins.
Before applying power, I cleaned the board thoroughly with 91% isopropyl alcohol and a stiff brush, then rinsed and dried it with compressed air. I also built the Apple Cassette Interface board, starting the same way by checking for shorts, then adding the resistors, sockets, capacitor, transistors, and ICs. That board checked out at 9.5K between 5V and ground, and I wired up the original-style audio jacks after verifying the correct terminal with a meter.
For power, I used original Stancor transformers mounted to a temporary board along with a fuse and switch. I tested the transformers on their own first and got 11.53 VAC from the 10V transformer and 33 VAC from the 28V transformer with no load. After crimping the connector pins and wiring the motherboard, I powered the board with no ICs installed and verified the rails at the DRAM sockets and character generator: -5V, +12V, +5V, and -12V were all present.
Then I populated the IC sockets, including the matched timing parts for the 74123, set the jumpers, and configured the PROMs for the memory test mode. The first power-up didn’t produce a display, and I found that one wire had pulled out of its crimp at the power connector. After fixing that, the board came up with blinking @ symbols, then reset properly and displayed the test output. I later returned the PROMs to normal configuration and got the expected backslash prompt.
The clone booted successfully, passed the memory test setup, and reached the normal monitor prompt. I also logged chip temperatures and found the 5V regulator ran hottest at about 80°C, while the system remained stable after running for several hours.
— Aaron
Links
Timestamps
00:00 – Intro
02:30 – First Look
05:30 – Test Power Rails
07:28 – Visual Inspection
10:45 – Resistors
14:31 – Sockets
16:51 – Ceramic Capacitors
18:17 – Reliability Mods
19:51 – Voltage Regulators/Large Caps
25:18 – Cleaning
27:09 – Apple 1 Cassette Interface
32:06 – Power Transformers
41:01 – Testing Voltages
43:05 – Adding ICs
47:52 – Jumpers
48:45 – Testing
53:12 – IC Temperatures
58:30 – Wrap Up/Next Steps