IIFX 1
This Macintosh IIFX “Reloaded” build, fresh from Bolle, initially presented a daunting challenge: It powered on, the fan spun, but beyond that, it was unresponsive – no chime, no video, no signs of life. While not completely dead, it was certainly in a coma. But as any seasoned tech knows, the silence (or in this case, the fan noise) is just the beginning of the story.
My diagnostic journey started with the fundamentals. I verified the RESET and HALT signals, confirming they were correctly transitioning low on reset and returning high. Next, I employed ZigZagJoe’s invaluable ROM diagnostic card. Unfortunately, the card was halting almost immediately after attempting to boot, indicating a deeper issue than a simple ROM problem.
With the ROM ruled out, I shifted my focus to clock signals. A thorough check revealed all expected clocks were present at their designated test points. This led me to suspect a potential problem with the OVERLAY signal, crucial for directing the CPU to the correct ROM location.
While probing for the VIA clock, I made a critical discovery. I was referencing the chip’s part number, not its board designation, and consequently, I was looking in the wrong place! I was missing the VIACLK signal entirely. A closer inspection of the board revealed a critical error: UD13 and UE13 were swapped. Correcting this oversight brought a glimmer of hope – the system now attempted to power on (the fan was already spinning), although it still wouldn’t chime.
I installed some SIMMs and connected my BlueSCSI. The system finally chimed! However, the NMI (Non-Maskable Interrupt) button behaved erratically. Pressing it resulted in no “death chime” unless it was pressed immediately after reset. This pointed towards a potential memory or interrupt controller issue.
At this point, I reached out to the board’s creator, Bolle, for guidance. He graciously pointed me to a crucial detail I had missed: jumper J103, which enables the SRAM, was not bridged. Bridging J103 proved to be the missing link. The IIFX finally chimed to life!
With a functioning system, I turned my attention to the remaining issue: the non-functional NuBus slots. SCSI was working flawlessly, but NuBus remained stubbornly silent. I verified the presence of the NuBus clock signal, which was indeed present. Despite having the correct clock, the NuBus cards were not recognized.
In a moment of desperation, I resorted to a technique familiar to many hardware troubleshooters: targeted reflow. I decided to reflow several TI chips, including two TI G(P?)ALs (Generic Programmable Array Logic). And, to my surprise, this seemingly random act proved to be the solution! After reflowing those two GALs, I powered on the system, and… video! The NuBus slots were now working.
While I still have some final testing to complete, this marathon troubleshooting session has hopefully reached its end. This experience highlights the importance of meticulous signal tracing, double-checking component placement, and sometimes, a little bit of luck. Thanks to Bolle’s expertise and a systematic approach, this Macintosh IIFX has been resurrected from its near-death experience!
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