Diagnostic Flowcharts, Signal Visualizer & Substitution Matrices
Measurement-driven troubleshooting suite combining interactive symptom decision trees (black screen diagnostics, bad RAM isolation, garbage screen charts), a virtual storage Oscilloscope & 8-Channel Logic Analyzer with Healthy-vs-Fault overlays, a Circuit Block Fault Simulator (TP1–TP5), a searchable DRAM/CPU/74-Series Substitution Matrix, and verified mainboard Recap Guides.
Step 3 Check: Probe D0–D7 during /CAS low. Mid-rail 1.8V steps indicate a shorted 4164/4116 DRAM output driver fighting the CPU.
Core Capabilities & Coverage
- Hardware Diagnostic Flowcharts for Commodore 64, ZX Spectrum 48K, and Game Boy DMG-01 with a synchronized side-panel Chip Pinout Inspector that updates at every test step.
- Universal Signal & Trace Visualizer offering Oscilloscope, 8-Channel Logic Analyzer, and Mixed-Signal (MSO) modes with Healthy vs. Fault trace comparison (Stacked or Side-by-Side Split) and live ΔV, ΔT, and frequency cursors.
- Circuit Block Visualizer modeling a 5-stage power and MCU signal chain (TP1–TP5) where you can inject four classic faults (blown fuse, leaky filter cap ripple, dead crystal clock, open MOSFET driver).
- Retro Logic & RAM Substitution Guide with a full Logic Family Compatibility Matrix (74LS, 74HCT, 74HC, 74ACT, 74F, 4000 CMOS) plus verified Recap & Repair Reference BOMs (/repair/{slug}).
Step-by-Step Workbench Workflow
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1
Select System & Symptom in the Diagnostic Flowchart
Open Hardware Diagnostics, choose your system (C64, ZX Spectrum 48K, or Game Boy DMG-01), and select your observed symptom (e.g., Black Screen, Garbage Characters on Boot, Dead Audio, or Corrupt Sprites).
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2
Take Physical Measurements (Multimeter, Logic Probe & Scope)
Follow each node's exact test instruction—measuring DC rails first (+5V, +12V, -5V), then checking /RESET release, CPU clock (Φ2 / CLK), and PLA/ULA chip-select strobes. Click any referenced IC in the right-hand inspector to view its exact pin location.
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3
Compare Live Waveforms in the Signal & Trace Visualizer
Click any quick-scope trigger button (or open /bench-tools/signal-visualizer) and toggle "Fault Overlay (Stacked)" or "Side-by-Side Split". Drag the vertical ΔT and horizontal ΔV cursors to measure ripple amplitude, clock frequency, or bus contention voltage levels.
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4
Verify Safe Replacement Parts & Capacitor Lists
Once you isolate the faulty IC or electrolytic capacitor bank, consult the Substitution Guide (/bench-tools/substitution-guide) to confirm safe drop-in equivalents (e.g., 74HCT replacing 74LS on TTL buses) and open the Recap Reference (/bench-tools/recap-repair-reference) for your board's verified capacitor BOM.
When diagnosing a "Black Screen" or stuck bus, switch the Signal Visualizer to Mixed-Signal (MSO) or Fault Overlay mode: a healthy TTL data line swings cleanly between <0.4V (VOL) and >3.4V (VOH), whereas a mid-rail plateau (~1.5V–2.2V) during a chip-select strobe is a classic signature of two ICs fighting on the bus.
74HC vs. 74HCT on NMOS/TTL Buses: Standard 74HC CMOS requires VIH >= 3.5V at 5V VCC, which an NMOS 6510, Z80, or 74LS output (guaranteed VOH >= 2.4V–2.7V) cannot reliably drive! Always use 74HCT (TTL-compatible VIH >= 2.0V) when substituting 74LS logic in vintage computers.