- Jan 28, 2016
This guide can be used on any NTSC N64 motherboard. The trim line is slightly different between board revisions however the relocations will be roughly the same. At first glance the trim might seem more daunting due to the PIF relocation but this actually simplifies the relocations to ensure that all the essential traces and components are reconnected. This also creates a universal relocation method between all the motherboard revisions. As the title says, this trim is an advanced level trim which should be performed by experienced modders to create smaller N64 portables.
How to choose which motherboard revision to trim:
Revisions 2-5 have 2x 2MB RDRAM ICs. This advantage means that they can be swapped with 2x 4MB RDRAM ICs for double the memory but without the added size increase of an expansion pak. Note that with this method you still need to use a jumper pak. 4MB RDRAM ICs can be harvested from OEM expansion paks or motherboard revisions 6-9. If there is no need to perform a ram swap, then there is little advantage which motherboard to use.
The Advanced N64 Trim
Note: Remove the PIF-NUS, U8, and U3 before trimming to avoid accidentally cutting them.
Voltage relocation for Standard Trim:
- Custom regulators (3.3V and 5V)
- 5V is only required if the original N64 video circuit is being used. 5V is not required if you are using a video replacement like ultraVGA or N64advanced with a digital audio amp.
- The 5V LDO (U13) should be removed if you are not wiring the input to 12V.
- All 3V3 spots must be reconnected.
Revisions 8-9: PIF-8 will be wired to Pin14 of U17
- It is easiest to reconnect PIF-6 to CPU-110 on the back side at these points by running a wire between them.
- PIF-6 must be connected to the spots on the cartridge slot, RCP, and CPU. PIF-7 must be connected to the spots on the cartridge slot and CPU.
- RST is the N64 Reset button and it is wired to a tactile switch and ground.
It is possible to relocate the PIF by cutting around it on the PCB. However, to ensure the minimum connections and components are made it is recommended to use the PIF Breakout Board. This can be purchased pre-assembled from the BitBuilt store, or you can build it yourself using the board files. https://store.bitbuilt.net/pif-breakout-pcb/
Minimum PIF circuit:
Note: The resistor and capacitor component designators in this schematic are not representative of the N64 motherboard.
Connect CPU-57 and CART-44 together. There is a 47Kohm Pullup resistor (R34) connected to these pins which will be preserved on the board for revisions 2-7. On the revisions 8-9 the resistor is cut off and will need to be replaced.
Cartridge Slot Relocation
Note: You must connect all the GND and 3V3 connections to the cartridge slot.
Pins 24 and 49 are not connected and do not need to be wired.
If the composite video signal color looks "washed out" on your screen, you may need to rewire the composite video filter: 75ohm resistor and 47pF capacitor forming a low-pass filter. R5/C13 on revisions 2-4 and FIL11/C13 on revisions 5-9.
Note: The N64 I2S digital audio sampling frequency can change per game and mid game and it does not have an master clock signal. One solution to be used in digital audio amps like the popular LM49450 is to use a PLL IC to generate the MC signal at a fixed ratio from WS.
Gman - Designed the Advanced trim, created all the diagrams, and tested the trims
Noah - Testing the Advanced trim and provided the stock N64 photos used in the diagrams
Stonededge - Testing the composite video filter and being one of the first to complete the advanced trim
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