Dragon Data
Interactive Flowchart Dragon 32 & Dragon 64
Mainboard + Power Regulator Daughterboard — Motorola MC6809E + MC6883 SAM + MC6847 VDG twin-board system
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
The Dragon 32 and Dragon 64 house their bridge rectifiers, bulk filter cans (4700 uF and 2200 uF), and +5V/+12V/-5V linear regulators on a separate upper power regulator board connected to the MC6809E mainboard.
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
Verify -5V and +12V rails on Dragon 32 boards fitted with 4116 DRAM
Early Dragon 32 boards using dual-bank 4116 / 4516 RAM require clean +12V and -5V rails from the regulator board.
Is This Your Board?
- Upper power regulator PCB sits at the rear right above the main logic PCB.
- Dragon 32 boards use either 4116 (+5V/+12V/-5V) or 4532/4164 DRAM; Dragon 64 uses eight 4164 DRAM chips and a 6551 ACIA.
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.
Upper Power Supply & Video Regulator Board
| Ref | Value | Voltage | Type | Function | Notes | Confidence |
|---|---|---|---|---|---|---|
C1 |
4700 uF | 25 V | Axial / Radial | +5V raw DC primary reservoir | Verified | |
C2 |
2200 uF | 25 V | Axial / Radial | +12V raw DC reservoir | Verified | |
C3 |
470 uF | 25 V | Radial | -5V / -12V negative reservoir | Verified | |
C4 |
100 uF | 16 V | Radial | +5V regulated output filter | Verified | |
C5 |
100 uF | 25 V | Radial | +12V regulated output filter | Verified |
Upper Power Supply & Video Regulator Board — shopping list
- 1 x 4700 uF 25 V Axial / Radial
- 1 x 2200 uF 25 V Axial / Radial
- 1 x 470 uF 25 V Radial
- 1 x 100 uF 16 V Radial
- 1 x 100 uF 25 V Radial
Dragon 32 / 64 Logic Mainboard
| Ref | Value | Voltage | Type | Function | Notes | Confidence |
|---|---|---|---|---|---|---|
C10 |
10 uF | 25 V | Radial | MC6809E /RESET delay timing | Verified | |
C14 |
22 uF | 25 V | Radial | DAC audio coupling | Verified | |
C18 |
100 uF | 16 V | Radial | MC6847 VDG / LM1889 chroma rail | Verified |
Dragon 32 / 64 Logic Mainboard — shopping list
- 1 x 10 uF 25 V Radial
- 1 x 22 uF 25 V Radial
- 1 x 100 uF 16 V Radial
Whole-Machine Shopping List
- 1 x 4700 uF 25 V Axial / Radial
- 1 x 2200 uF 25 V Axial / Radial
- 1 x 470 uF 25 V Radial
- 2 x 100 uF 16 V Radial
- 1 x 100 uF 25 V Radial
- 1 x 10 uF 25 V Radial
- 1 x 22 uF 25 V Radial
Recap Tips
- Reflow the multi-pin header pins joining the upper power board to the lower logic board - cracked solder joints here cause random resets.
Related Symptoms
- Rolling hum bar on composite video Dried-out C1 (4700 uF) or C2 (2200 uF) on the upper power regulator board.
Sources & References
- Dragon 32 & 64 Service Manual Official Dragon Data Ltd schematics.