Commodore 8-bit
Interactive Flowchart Commodore Plus/4 & C16 (TED)
Plus/4 ASSY 310163 & C16 ASSY 250443 — Commodore 264 Series TED mainboards
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
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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
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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
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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
The Plus/4 (ASSY 310163) uses an external C64-style +5V DC / 9V AC power brick (with a 4-pin square DIN on many units), whereas the Commodore 16 (ASSY 250443) takes 9V DC CENTRE-NEGATIVE via a barrel jack and regulates +5V internally.
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
Commodore 16 barrel jack is 9V DC CENTRE-NEGATIVE!
Never plug a standard modern centre-positive barrel adapter into a C16 or C116, and always fit copper heatsinks to the 7501/8501 CPU and 7360/8360 TED chip!
Is This Your Board?
- Plus/4 mainboard is ASSY 310163 with eight 4164 DRAM chips and four 28-pin ROM sockets.
- Commodore 16 mainboard is ASSY 250443 with two 4416 (16Kx4) DRAM chips and an internal 7805 regulator on a rear heatsink.
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.
Commodore Plus/4 Mainboard (ASSY 310163)
| Ref | Value | Voltage | Type | Function | Notes | Confidence |
|---|---|---|---|---|---|---|
C2 |
10 uF | 25 V | Radial | 7360 TED PLL filter | Verified | |
C11 |
10 uF | 25 V | Radial | Reset circuit timing | Verified | |
C20 |
470 uF | 16 V | Radial | TED audio output coupling | Verified | |
C50 |
2200 uF | 16 V | Axial | 9V AC rectifier / cassette motor rail | Verified | |
C51 |
100 uF | 16 V | Radial | +5V logic rail filter | Verified | |
C52 |
470 uF | 16 V | Radial | +5V secondary decoupling | Verified |
Commodore Plus/4 Mainboard (ASSY 310163) — shopping list
- 2 x 10 uF 25 V Radial
- 2 x 470 uF 16 V Radial
- 1 x 2200 uF 16 V Axial
- 1 x 100 uF 16 V Radial
Commodore 16 Mainboard (ASSY 250443)
| Ref | Value | Voltage | Type | Function | Notes | Confidence |
|---|---|---|---|---|---|---|
C10 |
2200 uF | 25 V | Axial | 9V DC input primary reservoir | Verified | |
C11 |
470 uF | 16 V | Radial | 7805 +5V output reservoir | Verified | |
C14 |
10 uF | 25 V | Radial | 555 /RESET timing | Verified | |
C25 |
10 uF | 25 V | Radial | TED video/PLL filter | Verified | |
C41 |
220 uF | 16 V | Radial | Audio coupling to RF modulator | Verified |
Commodore 16 Mainboard (ASSY 250443) — shopping list
- 1 x 2200 uF 25 V Axial
- 1 x 470 uF 16 V Radial
- 2 x 10 uF 25 V Radial
- 1 x 220 uF 16 V Radial
Whole-Machine Shopping List
- 4 x 10 uF 25 V Radial
- 3 x 470 uF 16 V Radial
- 1 x 2200 uF 16 V Axial
- 1 x 100 uF 16 V Radial
- 1 x 2200 uF 25 V Axial
- 1 x 220 uF 16 V Radial
Recap Tips
- On the C16, upgrade the 7805 linear regulator to a 1.5A/2A switching buck regulator (Traco TSR 2-2450) to eliminate the massive heat load inside the case.
Related Symptoms
- Black screen after 5 minutes of operation Thermal failure of the un-heatsinked 8501 CPU or 7360 TED.
Sources & References
- Console5 TechWiki - Commodore Plus/4 & C16 ASSY 310163 and ASSY 250443 capacitor lists.