In this follow-up from CRG, the spotlight is on an A3640 accelerator repair inside a recently revived Amiga 4000. After restoring the system from heavy battery damage in part one, the next hurdle is getting the faulty A3640 CPU card to run reliably. The process reveals unexpected issues, from reversed capacitors to power supply quirks, before the accelerator finally roars back to life.
Correcting Earlier Mistakes
Before working on the accelerator, CRG spots a mistake from the prior repair—two capacitors were installed following incorrect silk screen markings. Reversing them prevents potential failure and sets the stage for a more focused A3640 accelerator repair.
Tracking the A3640 Fault
Tests show the system refusing to power with the A3640 installed, suggesting a possible short. The card has had electrolytics replaced with ceramics, which behave differently. CRG reinstalls proper electrolytics, cleans capacitor leakage, and reflows suspect ICs. Continuity checks confirm patch wiring is correct, but the board still refuses to boot.
The PSU Surprise
After hours of troubleshooting, the issue turns out to be the ATX power supply. Without enough load on the 12V rail, it shuts down. Adding extra hard drives provides the necessary draw, and the A3640 finally boots.
Testing Zorro and IDE
With the accelerator running, CRG tests Zorro slots and storage. A Zorro IDE card boots fine, but the onboard IDE struggles with Workbench 3.1, working only after installing Workbench 3.0—likely a ROM driver quirk.
Keyboard Port Fix
A faulty PS/2-to-AT keyboard adapter has reversed wiring. After rewiring, the keyboard works perfectly, confirming another subsystem’s health.
Wrapping Up
By the end of this A3640 accelerator repair, the Amiga 4000 has a functioning CPU card, operational Zorro expansion, working onboard IDE with the right OS version, and a responsive keyboard. Future upgrades will include installing AmigaOS 3.2, sourcing an original case, and possibly enhancing the accelerator for better performance.
