Editing Super Famicom Maintenance Guide (section)

== Nintendo's diagnostic table ==

From Nintendo's own service manual. The probable causes are in Nintendo's order of priority, which is itself useful information — Nintendo put the cartridge connector at the top of three separate faults.<ref name="nintendodiag" />

Nintendo prefaces it: before attempting any repair, strip the unit and inspect the PCB thoroughly for damaged or missing components and traces, solder defects, dirt and corrosion.

{| class="wikitable styled-table" style="width:100%;"
|+'''Control deck — malfunctions and probable causes'''
! Malfunction !! Probable causes, in order
|-
| Solid colour screen (a black screen counts here) || 62-pin connector; sound module; poor solder; U1 (CPU); U3 (PPU2); U6 (WRAM); U2 (PPU1); U7 (RGB encoder); X1 (21 MHz oscillator); U8 (CIC)
|-
| Scrambled video images || 62-pin connector; poor solder; U3 (PPU2); U1 (CPU); U2 (PPU1); U4 or U5 (256K SRAM)
|-
| Distorted or no sound || Sound module; connector P5; U1 (CPU); U10 (amplifier); Q18
|-
| No reset (the system reset line, not the button) || U8 (CIC); X2 (4 MHz oscillator); U9 (74HCU04)
|-
| Poor or no colour || Defective TC1 — the master clock must be adjusted to the correct frequency (see below); U3 (PPU2); U7 (RGB encoder); X1 (21 MHz oscillator)
|-
| No power || F1 (1.5 A fuse); D1; T1 (line filter); U12 (7805 regulator); VA1 (surge absorber); Q18; P3 (power switch)
|-
| Snowy screen || RF modulator
|-
| Intermittent or no controller operation || Front unit PCB assembly; FFC harness (flat cable); connector P2; U1 (CPU)
|-
| Frozen screen or erratic program operation || 62-pin connector; poor solder; U1 (CPU); U3 (PPU2); U2 (PPU1)
|-
| Ejector will not eject game paks || Early-version ejector — Nintendo's instruction was to replace on customer complaint only
|}

Nintendo notes that a few of the power-section parts were eliminated over the machine's production life, so not every board has a D1, T1, VA1 or Q18.<ref name="nintendodiag" />

=== TC1 and the master clock ===

'''TC1 is a trimmer capacitor, and it is adjustable.''' If a console has poor or no colour and everything else checks out, Nintendo's remedy is to set the master clock at TC1 — and the target frequency depends on the television standard the console was built for, because the NES and SNES derive colour from a master clock at six times the colour subcarrier.

The Playtronic manual is a Brazilian document and therefore gives the '''PAL-M''' figure: approximately '''21.453666&nbsp;MHz'''. Its colour-fault tree tells the technician to check the oscillation frequency first, and if the adjustment is impossible or unstable to replace TC1 and then X1.<ref name="nintendodiag" />

For other markets the corresponding master clock frequencies are '''21.47727&nbsp;MHz''' on an NTSC or Japanese machine, and a '''17.734475&nbsp;MHz''' crystal on a European PAL SNES, from which the S-CLK chip synthesises the PAL master clock.<ref name="fullsnes" />

Do not apply the Brazilian figure to a Japanese or North American console: they are close enough to look plausible and far enough apart to give you a colour fault.

=== Nintendo's colour-fault tree ===

Nintendo's own sequence, worth following because it separates the RF path from the direct video path early.<ref name="nintendodiag" />

* '''Monochrome picture.''' Check the oscillation frequency. If it cannot be adjusted or will not hold, replace TC1, then X1.
* '''Only the RF output is wrong.''' Replace the RF modulator.
* '''Both RF and direct outputs are wrong.''' Inspect the discrete components around the RGB encoder (U7) for solder defects and damage, then replace U7, then PPU2 (U3).
* '''Colour cast — reddish, bluish and so on, on RGB, S-Video and composite together.''' Probable causes are a defective PPU2 or a missing or interrupted red, green or blue signal out of the RGB output. Check around the transistors that amplify the RGB signal (Q3 to Q9) for solder defects and damage, then replace PPU2 (U3).
* '''Only the BG6 image signal is normal.''' Probable causes are a defective RGB encoder or defective colour signal filters at C14 and C16. Inspect the discrete components around U7, then replace U7.