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Nintendo Entertainment System R2 Video Resistor Replacement

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NES-001 R2 video resistor (NES-CPU-07)
R2 on an NES-CPU-07 board, silkscreened 510, below the 74HCU04 (U9); Q1 (A937) is at top left (crop of a photo by Evan-Amos, public domain)

Early mainboards of the front-loading NES-001 Nintendo Entertainment System can lose colour from the picture because of one resistor. Nintendo's Service Department Bulletin 91205 says that Control Deck PCB versions 1 to 3 have a 2.2 kΩ video output resistor at R2, that in some circumstances this resistor causes a loss of colour or a colour wash-out in the video from the PPU, and that the repair is to replace R2 with a 510 Ω resistor.[1] Later boards were built with 510 Ω: the NES-CPU-07 board in the photograph has "510" printed beside R2.[2]

R2 is part of the video output stage. In a redrawn NES-001 schematic the PPU's video output on pin 21 drives the base of transistor Q1 (2SA937), R2 (510 Ω) connects Q1's emitter to +5 V, and the emitter feeds the video output line through FC2.[3]

Symptoms

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  • The picture lacks colour or the colours look washed out, on a console with an early mainboard.[1]

A picture that is scrambled, a solid colour or blank is a different fault: Nintendo's technician fault table puts those down to parts that include the PPU, the video RAM, the CPU, Q2 and the RF modulator. See the Nintendo Entertainment System Troubleshooting Guide.[4] The bulletin covers Control Deck PCB versions 1 to 3 only.[1]

Safety

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  • Unplug the AC adapter before opening the console.
  • The metal shields are very sharp; Nintendo recommends gloves.[5]

Tools and parts

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  • A 510 Ω through-hole resistor.[1]
  • A Phillips screwdriver, a soldering iron, solder and desoldering braid or a desoldering pump.
  • A multimeter, to check the old resistor's value.

Procedure

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NES-001 video buffer Q1 and R2 (Schenk redraw)
The video output stage in a 2020 redraw of the NES-001 schematic: PPU pin 21, Q1 and R2
  1. Open the console and lift out the mainboard as described in steps 1 to 8 of Nintendo Entertainment System 72-Pin Connector Replacement#Disassembly. The 72-pin connector can stay on the board.[5]
  2. Lay the board component side up and read the board revision printed on it (NES-CPU-xx).[6] Bulletin 91205 refers to the affected boards only as PCB versions 1 to 3.[1]
  3. Find R2 by its silkscreen label. On the NES-CPU-07 board in the photograph it lies just below U9, the 74HCU04P, with Q1 (A937) above U9.[2] On a board with a different layout, follow the track from Q1's emitter.[3]
  4. Check R2's value. If it is 2.2 kΩ, continue; if it is already 510 Ω, the bulletin does not apply.[1]
  5. Desolder R2 and remove it.
  6. Fit the 510 Ω resistor in its place and solder it.[1]
  7. Reassemble the console as described in Nintendo Entertainment System 72-Pin Connector Replacement#Reassembly.

Testing

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  • Connect the console to a television through the A/V output and through the RF output in turn, and check that the colours are correct on both. Nintendo's own test procedure ends with a check for clear output on video and on RF channels 3 and 4.[7]
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Nintendo of America, Service Department Bulletin #91205, "Control Deck Repair: Video Output Resistor (R2) Enhancement", one page, undated. Hosted as File:Nintendo Service Bulletin 91205 NES Video Output Resistor R2.pdf; see Nintendo NES Service Bulletins.
  2. ↑ 2.0 2.1 Evan-Amos, "Nintendo-NES-Mk1-Motherboard-Top.jpg", Wikimedia Commons, public domain (retrieved 2026-10-25). NES-CPU-07 board; R2 with "510" printed beside it, below U9 (74HCU04P); Q1 (A937).
  3. ↑ 3.0 3.1 N. Schenk (Schenktronics), NES Schematics, file Original_NES.sch, rev. 1.0, 2020-06-05: PPU U5 pin 21 (VOUT), Q1 2SA937, R2 510 Ω to +5 V, FC2, C5 330 pF, VIDEO_OUT and AUX_VIDEO_OUT. Hosted as File:NES-001.pdf; see NES-001 Schematic.
  4. ↑ Nintendo of America, NOA Independent Servicer Technical Training Workbook, Rev. 11/90, "Malfunctions and Probable Causes", pp. 54-55. Hosted as File:NES WCS HQ.pdf; see NOA Independent Servicer Technical Training Workbook.
  5. ↑ 5.0 5.1 Nintendo of America, Authorized Service Center Manual, revision June 2002, chapter 4, disassembly procedure, pp. 26-28. Hosted as File:Nintendo Authorized Service Center Manual June 2002.pdf.
  6. ↑ Mark Knibbs, Disabling the NES "Lockout Chip", rev. 0.4, 22 September 1997, steps 7 and 8: turning the board component side up and reading the revision printed in white near its centre, for example NES-CPU-11.
  7. ↑ Nintendo of America, NOA Independent Servicer Technical Training Workbook, Rev. 11/90, "Control Deck testing procedure", step 10, p. 54. Hosted as File:NES WCS HQ.pdf.
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