Repair assistant

A diagnostic bench for amplifiers and electronic devices.

Choose the device, follow the signal or power path, compare symptoms, and move one safe measurement at a time.

Safety first, always.

ElectroLab AI teaches theory, low-voltage electronics, and planning concepts. Mains voltage, switchboards, fixed wiring, high-current systems, and legal electrical work must only be performed by licensed electricians where required.

Open Safety Center

Probe path

Trace from source to load, then from input to speaker.

The repair bench now covers vintage amps, modern class D gear, tube amp boundaries, speakers, supplies, battery devices, and controller boards.

Open troubleshooting coach Open signal tracer

Diagnostic bench

Choose the device, pick the symptom, then follow the next safe test point.

Built for audio amplifiers first, but useful for speakers, supplies, battery gear, and controller boards.

Open guided coach

Selected device

Vintage class AB amplifier

Transformer supply, rectifier, big filter capacitors, input selector, preamp, driver board, output transistors, and speaker relay.

Open related lab

Pick the symptom

First move

Relay will not click / protect stays on

Disconnect speakers, set volume down, and check DC offset at the speaker terminals before assuming the relay is bad.

Measurement sequence

TP1: Speaker terminals

DC volts

Change one thing after this reading

ExpectedNear 0 V DC after startup

If wrongHigh DC means do not connect speakers. Compare left and right output stages.

TP2: Positive and negative rails

DC volts

Change one thing after this reading

ExpectedBoth rails present and similar magnitude

If wrongOne missing rail points to rail fuse, rectifier, cap, or shorted output section.

TP3: Relay coil

DC volts

Change one thing after this reading

ExpectedCoil voltage appears after delay

If wrongProtection circuit may be holding relay off because it sees DC or missing rail.

TP4: Emitter resistors

Millivolts DC

Change one thing after this reading

ExpectedSmall balanced voltage drop at idle

If wrongLarge or uneven drop suggests bias/output transistor trouble.

Pattern clues

Old amps often fail mechanically: dirty selectors, cracked solder, oxidised relay contacts, tired electrolytics.

Compare left and right channels. A good channel is the best schematic annotation you own.

Use a dim-bulb tester or current-limited setup only if you know how; it can save outputs after repair.

Stop rules

Live internal checks on mains-powered amplifiers are for trained people with isolation, one-hand habits, and proper probes.

Large filter capacitors can hold charge after unplugging.

Do not connect valuable speakers until DC offset and protect behaviour are known.

Use the bench tools

Meter labChoose voltage, resistance, continuity, and diode checks.Signal tracerFollow audio or control signals from source to load.Schematic readerTurn the device path into a readable map.Lab notebookRecord each reading before changing parts.

This repair flow is educational guidance. Live mains, high-voltage rails, tube amps, and legal electrical work require qualified people and proper safety equipment.