MSX Standard
Interactive Flowchart MSX (MSX1 / MSX2 / MSX2+ / Turbo R)
Sony HB / Philips NMS / Panasonic FS-A1 (MSX2 / MSX2+ / Turbo R) — Z80A / R800 + TMS9918A / V9938 / V9958 VDP + AY-3-8910 / YM2149
Complete Diagnostic Flowchart: Capacitive Load, ESR & Power Rail Ripple Diagnostic Tree (Universal Retro Mainboards (C64, Amiga, ZX Spectrum, Game Gear, Consoles))
STEP 1: Measure 100Hz/120Hz Peak-to-Peak AC Ripple on the +5V / +12V Bulk Filter Cap
[node-1]
Set your oscilloscope to AC Coupling, 200 mV/div, and 2.5 ms/div (20 MHz bandwidth limit ON). Probe directly across the main bulk filter capacitor (e.g. C19 2200µF / C88 1000µF on C64, or C303/C304 on Amiga) under full system load. Measure the peak-to-peak sawtooth ripple amplitude (mVpp).
Expected Reading: < 50 mVpp clean regulated rail (post-regulator) or < 350 mVpp on raw unregulated bulk DC before the 7805/7812.
STEP 2: Check Linear Regulator (7805 / 7812) Input-to-Output Dropout Margin
[node-2]
Switch oscilloscope or multimeter to DC Volts and measure Pin 1 (Input) of the 7805 (+5V) or 7812 (+12V) regulator at the bottom of the ripple trough. Verify that Input Voltage remains at least 2.0V above the regulated output (e.g. ≥7.2V into a 7805, ≥14.2V into a 7812).
Expected Reading: 7805 Input ≥ 7.2V DC; 7812 Input ≥ 14.2V DC. Below this dropout threshold, ripple punches straight through to the logic rail.
STEP 3: Check Local IC Decoupling & Audio/Video AC Coupling Capacitors
[node-3]
Probe audio output coupling caps (e.g. C91 100µF on C64 SID Pin 27, or C324/C334 22µF SMD on Amiga Paula) — compare upstream vs. downstream signal amplitude. Inspect SMD electrolytic pads (Amiga 600/1200, Game Gear, DMG-01) under magnification for fishy odor, dull grey solder corrosion, or lifted copper traces.
Expected Reading: Full audio/video swing across the coupling capacitor with zero DC leakage on the output side and clean, shiny solder pads.
[ISOLATED FAULT: RES-BULK-CAP] Fault Isolated: High-ESR Bulk Filter Capacitor (>100 mVpp Rail Ripple)
VERDICT
Excessive 100/120Hz sawtooth ripple on the DC rail confirms that the primary reservoir/filter electrolytics have dried out and lost effective capacitance.
[ISOLATED FAULT: RES-REG-DROPOUT] Fault Isolated: Linear Regulator Dropout / Bridge Rectifier Diode Open
VERDICT
The pre-regulator DC rail is sagging below the minimum 2V dropout headroom required by the 7805/7812 regulator.
[ISOLATED FAULT: RES-COUPLING-CAP] Fault Isolated: Open/Leaky Audio or Video Coupling Capacitor & Trace Corrosion
VERDICT
Signal attenuation, muffled audio, or DC offset hum across the coupling stage indicates dried-out or leaking coupling capacitors.
[ISOLATED FAULT: RES-RAILS-HEALTHY] Verification Passed: Power Rails, Ripple & Coupling Capacitors Within Spec
VERDICT
All measured DC supply rails, AC ripple levels (<50 mVpp), and coupling stages pass bench specification. If performing a preventive recap, use the verified board BOM below.
Summary
MSX1 and early MSX2 machines use reliable through-hole radial capacitors, whereas late-era Japanese MSX2+ (Sony HB-F1XDJ/XV, Panasonic FS-A1WX/WSX) and MSX Turbo R (FS-A1ST/FS-A1GT) boards use surface-mount quaternary-salt electrolytics that leak and corrode video DAC and FM-PAC audio traces.
Interactive Bench Oscilloscope — Verify Pre- & Post-Recap Waveforms
Open Full Signal Visualizer →Click any test point below to compare a healthy recapped rail or clock against high-ESR electrolytic capacitor ripple and droop:
Safety & Warnings
Remove the NiCd RTC battery on MSX2 boards immediately
MSX2 systems with real-time clock settings (RP5C01) carry a 3.6V NiCd battery that leaks alkaline electrolyte across the V9938 VDP and S1985/MSX-SYSTEM II ASIC.
Is This Your Board?
- Check around the V9938/V9958 VDP and CXA1145/AN5265 video encoder for miniature silver SMD cans (Panasonic FS-A1 series) or leaked NiCd RTC batteries (MSX2 RP5C01).
Verified
Check
Verified rows are agreed by two or more independent sources. Check rows are revision-dependent or single-sourced — confirm the value against your own board before ordering.
MSX2 / MSX2+ / Panasonic FS-A1 Mainboard Reference
| Ref | Value | Voltage | Type | Function | Notes | Confidence |
|---|---|---|---|---|---|---|
C101 |
1000 uF | 16 V | Radial | +5V DC logic primary reservoir | Verified | |
C102 |
470 uF | 25 V | Radial | +12V DC cartridge slot & video rail | Verified | |
C103 |
100 uF | 25 V | Radial | -12V DC cartridge slot rail | Verified | |
C201 |
10 uF | 25 V | Radial / SMD | Z80A /RESET timing | Verified | |
C301 |
22 uF | 25 V | Radial / SMD | AY-3-8910 / YM2149 PSG audio coupling | Verified | |
C302 |
22 uF | 25 V | Radial / SMD | YM2413 OPLL FM-PAC audio mix coupling | Verified | |
C401 |
47 uF | 16 V | Radial / SMD | V9938 / V9958 RGB & Composite video clamp | Verified | |
C402 |
100 uF | 10 V | Radial / SMD | Composite video output coupling | Verified |
MSX2 / MSX2+ / Panasonic FS-A1 Mainboard Reference — shopping list
- 1 x 1000 uF 16 V Radial
- 1 x 470 uF 25 V Radial
- 1 x 100 uF 25 V Radial
- 1 x 10 uF 25 V Radial / SMD
- 2 x 22 uF 25 V Radial / SMD
- 1 x 47 uF 16 V Radial / SMD
- 1 x 100 uF 10 V Radial / SMD
Recap Tips
- Note that Japanese MSX RGB21 cables use a different pinout from European Euro-SCART cables - never plug a JP-21 cable directly into a European SCART TV!
Related Symptoms
- Dark or rolling composite video on Panasonic FS-A1WX/GT Leaked SMD video coupling capacitors C401/C402 near the video encoder.
Sources & References
- MSX Resource Center - Hardware Service Manuals Sony, Philips, and Panasonic MSX service manuals.