Test Mode
Test mode is a built in hardware testing feature. Almost every input/output pad can be tested individually with a simple pass/fail test. To activate test mode, first remove the NESRGB board from the console, close solder jumper JP12, and insert tactile switch SW1 (you can solder it, but it's not necessary). Solder a wire to the "TP" (test probe) solder point near the R video output. I recommend attaching a stick of some kind to the free end to make probing easier. A +5V power source is required to power the board during testing. You can use the NES console (PPU pin 40 is +5V, pin 20 is GND) or a regulated bench power supply. The voltage and polarity of the power wires must be correct. Measure with a multimeter before connecting the NESRGB board if you have any doubt.
The NESRGB board may have an IC socket or adapter board attached. It must not be installed into a console or have a PPU attached. If the PPU is soldered on then desolder it with solder wick or a solder sucker. It's much easier to remove from the NESRGB board than a NES motherboard.
Power up the NESRGB board with JP12 closed it it will go into test mode
immediately. You will know it because all the LEDs will come on. Now
probe each pin in turn, and look at the LEDs for the result. Green means
pass, red means fail, and the current test number is shown on the orange
LEDs in binary. Each test is for one pin only and will run continuously.
Press switch SW1 to go to the next test. Below is a list of all tests,
including the number and the pin that should be probed. It is safe to
probe the wrong pin on any given test, it will just report as a failure.
| Orange LEDs | Test number and description | Fault nr. |
     |
0. Visual LED test. All seven LEDs come on (one green, one red,
five orange). The probe is unused. |
1 |
    |
1. Probe GND, pin 20. (for testing the probe input) | 2 |
 |
2. Probe +5V, pin 40. (for testing the probe input) | 2 |
| |
3. Probe R/W#, pin 1. |
3 |
| |
4. Probe D0_BUS, pin 2M. | 4 |
| |
5. Probe D1_BUS, pin 3M. | 4 |
| |
6. Probe D2_BUS, pin 4M. | 4 |
| |
7. Probe D3_BUS, pin 5M. | 4 |
| |
8. Probe D4_BUS, pin 6M. | 4 |
| |
9. Probe D5_BUS, pin 7M. | 4 |
| |
10. Probe D6_BUS, pin 8M. | 4 |
| |
11. Probe D7_BUS, pin 9M. | 4 |
| |
12. Probe D0_PPU, pin 2P. | 5 |
| |
13. Probe D1_PPU, pin 3P. | 5 |
| |
14. Probe D2_PPU, pin 4P. | 5 |
| |
15. Probe D3_PPU, pin 5P. | 5 |
| |
16. Probe D4_PPU, pin 6P. | 5 |
| |
17. Probe D5_PPU, pin 7P. | 5 |
| |
18. Probe D6_PPU, pin 8P. | 5 |
| |
19. Probe D7_PPU, pin 9P. | 5 |
| |
20. Probe A2, pin 10. |
3 |
| |
21. Probe A1, pin 11. | 6 |
| |
22. Probe A0, pin 12. | 6 |
| |
23. Probe CS#, pin 13. |
6 |
| |
24. Probe EXT0, pin 14P. |
6 |
| |
25. Probe EXT1, pin 15P. | 6 |
| |
26. Probe EXT2, pin 16P. | 6 |
| |
27. Probe EXT3, pin 17P. | 6 |
| |
28. Probe CLOCK_PPU, pin 18P. |
7 |
| |
29. Probe CLOCK_IN, pin 18M. | 8 |
| |
30. Probe INT#, pin 19. |
6 |
| |
31. Probe VIDEO_PPU, pin 21. |
9 |
|
32. Probe RESET#, pin 22. |
3 |
| |
33. Probe OVIN video input. |
2 |
| |
34. Probe CS# sync output. | 7 |
| |
35. Probe R video output. |
10 |
| |
36. Probe G video output. | 10 |
| |
37. Probe B video output. | 10 |
| |
38. Probe VS video/sync output. | 11 |
| |
39. Probe Y video output. | 10 |
| |
40. Probe C video output. |
10 |
| |
41. Probe LED output. |
2 |
| |
42. Probe RO reset output. |
2 |
| |
43. Probe 1D controller input. |
2 |
| |
44. Probe 2C controller input. | 2 |
| |
45. Probe 3L controller input. | 2 |
| |
46. Probe will output 3.5 KHz triangle wave audio tone. This is
not a pass/fail test, just a crude way to test the audio path.
Connect probe to '46', 'A', 'B' audio inputs while AO output is
connected to an audio amplifier. Warning - the output is rather
loud. |
- |
To make the process easier, here are the exact locations where to probe for each test. The optimal locations are different depending on whether or not there is an IC socket attached.
No socket:
IC socket present:
Here is are the relevant pin locations on the left hand side of the board.
Here is some info about which IC is connected to each pin. This may be useful to repair damaged boards.
| Fault nr. |
The possible cause or IC connected to this input/output. |
| 1 |
If a LED does not light during the visual LED test, the LED
itself may be faulty. |
| 2 |
MCU. |
| 3 |
Level translator U2 SN74LVC541APW. |
| 4 |
Level translator U3 SN74LVC4245APW. |
| 5 |
Level translator U9 SN74LVC4245APW. |
| 6 |
Level translator U1 SN74LVC541APW. |
| 7 |
FPGA. |
| 8 |
Schmitt trigger U15 SN74LVC1G17DCKR (NESRGB50) or
SN74LVC1G17DBVR (NESRGB51). |
| 9 |
Video input analog section. U10 GS8051-TR (alt. OPA356AIDBVR),
U11 GSV331-TR (alt. MCP6561UT-E/OT), U12 MX3502S (alt.
TLV3502AIDR). |
| 10 |
Video driver U17 THS7374IPW. |
| 11 | Video driver U8 GS8051-TR (alt. OPA356AIDBVR). |
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Last updated 19/5/2026.