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Product identity and typical ratings
• Board code: DVO-3A (often found inside Delta laptop adapters such as DPS-160AP-2 or TV/monitor PSUs).
• Nominal output in most builds: 18–20 V DC @ 3–4 A.
• Topology: single-transistor flyback or quasi-resonant forward converter, no active PFC in early versions, full-wave bridge and bulk cap on the primary.
Block-level architecture you will find on the PCB
a. Mains input / EMI filter → bridge rectifier → 400 V bulk electrolytic.
b. Startup & PWM controller (often UC3842/3843, L6599, or Delta-labelled ASIC).
c. Primary MOSFET on heatsink.
d. Isolated flyback transformer.
e. Secondary Schottky rectifier(s) → LC filters.
f. Feedback: TL431 precision shunt + optocoupler.
g. Stand-by/housekeeping winding that powers the controller once the converter has started.
Reverse-engineering workflow if no schematic is available
• Photograph both sides in high resolution, straighten images and mirror the solder side.
• Mark isolation barrier; trace primary first.
• Identify controller IC, download its datasheet – pin functions give you half the schematic instantly.
• Trace the feedback loop (TL431, opto, divider). The TL431 equation gives you the exact output-set resistors:
\[ V{out}=V{ref}\left(1+\frac{R{\text{upper}}}{R{\text{lower}}}\right)\], with \(V_{ref}=2.495 \text{V}\).
• Draw the netlist in KiCad/Eagle or a free tool such as EasyEDA; photograph-to-schematic plug-ins can speed up.
• Verify with continuity-beep and DMM resistance.
Typical failure modes & component suspects (statistics from Delta adapter repairs)
• Primary MOSFET short → blown fuse.
• Startup electrolytic (10–47 µF/50 V) dries out → controller never reaches Vcc start threshold.
• Optocoupler CTR drop → over-voltage or oscillatory output.
• Secondary Schottky short → hiccup or burst-mode clicking.
• Large bulk cap (100–150 µF/400 V) ESR rise → audible buzz, thermal stress.
Diagnostic sequence without schematic
Modifying output voltage (common request: 20 V → 12 V)
• Safest path: leave PSU untouched, add an external DC-DC buck module.
• If you insist on internal change: adjust TL431 divider (increase bottom resistor to lower Vout). Must recalc compensation network and ensure magnetic design, rectifier current & opto gain stay within spec.
• Manufacturers have tightened documentation control; laptop and LED-TV adaptor schematics are rarely published.
• Professional repairers increasingly use AI-assisted image-to-netlist tools to speed up reverse engineering of SMPS PCBs.
• Component substitution: wide-range 650 V GaN FETs and synchronous rectifiers are becoming common in new Delta designs; older DVO-3A remains silicon-based.
• Why Delta keeps it private: competitive IP, UL/TÜV safety file, and liability if unqualified repair leads to hazards.
• Isolation gap: ≥6 mm creepage on PCB—never bridge it while probing.
• Series-bulb tester analogy: an incandescent bulb acts like a big resistor whose resistance rises with current, protecting the DUT.
• Schematics are Delta’s copyright; unauthorised distribution can breach IP law.
• Working on off-line SMPS exposes >300 V DC; EU Low-Voltage Directive and OSHA require competent personnel and isolation transformers during service.
• Always discharge primary cap with 100 Ω / 5 W resistor before handling.
• Use an isolation transformer plus differential probe if you must scope the primary.
• Replace electrolytics with 105 °C low-ESR parts from reputable brands; match ripple current spec.
• After repair, perform a 2 kV HIPOT between primary and secondary to verify insulation integrity.
• Because no public schematic exists, component designators differ between production runs; confirm values on the actual PCB.
• Some boards marked DVO-3A were built for active-clamp forward topology—parts list may vary.
• Datasheets cited here (UC3842, TL431, etc.) illustrate common practice but may not match every revision.
• Post macro photos of both PCB sides on technical forums (EEVblog, BadCaps) to crowd-source partial schematics.
• Study ON-Semi Application Note AND9136 (flyback design) to understand the math behind resistor networks and transformer parameters you may measure.
• Explore open-source tool “OpenScope-X-Ray” for automated trace extraction from board images.
The Delta B/ PEC DVO-3A schematic is not publicly available; Delta releases it only under NDA. Effective repair therefore relies on generic SMPS knowledge and board-level reverse engineering. Identify functional blocks, leverage controller datasheets, and follow safe diagnostic procedures. If output modification is needed, external DC-DC conversion is usually safer than altering the closed-loop divider inside the adapter.
