• Leaky Ni-Cd clock battery

The Ni-Cd battery may be leaking, risking damage to PCB layers & nearby components. Promptly remove the battery & clean corrosion/alkaline salts from the board. Use white vinegar to dissolve salts, but exercise caution as vinegar can corrode exposed metals. A thorough examination & repair may be needed. Replace battery with guide: https://github.com/wiretap-retro/Not-A-Varta

AH4/AH4T/AN4R2 share the same bios

For the boards missing a VRM for 3.3V operation, here's the part list to re-implement the feature (thanks Madao !):

• Q4 = LT1085-ADJ or pin-compatible type with Low Dropout(LD1085V from ST, EZ1084, ...)
• TC15 = 10µF condensator
• TC12 = 150µF (recommended by LT1085's datasheet)
• JP52, bridged with wire by soldering.
• R77 = 270 Ohm, 4V CPU voltage, Jumper JP53
• R78 = 240 Ohm, 3.6V CPU voltage, Jumper JP54
• R79 = 220 Ohm, 3.45V CPU voltage, Jumper JP55
• R80 = 200 Ohm, 3.3V CPU voltage, Jumper JP56
• R81 = 127 ohm
• R41 and R42 is placed with 10 Ohm resistance (my estimated value) Location: between VLB slot and CPU socket