Entryphone 9200 Series: One-Way Audio Fault Finding

Written from two real jobs on the same type of system: a blown DC fuse (first job) and failed door panel amplifier boards on both entrances of a six-flat block (second job). Do the free tests first. Swap the board last.

System Overview

Terminal Reference

Door unit (92ETXAMP)

On the Ver 5 board the terminal block reads E, C, D from top to bottom, the reverse of the old DCE moulding. Always wire by the printed label, never by position.

Phones

Mains unit (DA2H)

Fuses: 1.0A mains, 2.0A AC output, 0.8A DC output.

95(V)RU relay unit

Strip labels: 3, L, P (phones side), then E1, E2, D1, D2, CBP1, CBP2, CBP/AC, LOCK1, LOCK2 (door units).

• There is no C terminal on the strip. Use the mains unit DC negative as your meter reference.
• CBP1 and CBP2 are the call bell-push lines, not a common. CBP/AC is the AC supply, not an audio reference.
• D1 and E1 are door unit 1. D2 and E2 are door unit 2. Work out which physical panel is which before testing.

How the Speech Circuit Works

Speech is DC powered.

• Visitor to flat: DC positive through the phone receiver, then L, then the relay contacts, then D, then the door microphone, then C.
• Flat to visitor: the phone microphone, then P, then the relay, then E, then the door speaker, then C.

So a failed door board, a loaded-down line or a worn relay contact on the D to L path can kill visitor-to-flat while flat-to-visitor still works. The AC you see on the relay unit terminals is the ringing and lock supply and tells you nothing about speech.

Relay Unit With Two Entrances

Field observation, one site: with a relay unit in the communal cupboard, only the door unit being called is switched on. The door microphone and speaker do not become active until a call is made from that panel, and the two entrances cannot be in use at the same time. When one call ends and another entrance is called, the relay switches to that door.

What this means when testing:

• Take your readings during a live call from the panel you are testing. Idle readings on a panel that is not being called can look dead when it is not faulty.
• Always note whether the reading was taken at idle or in a call.

Fault Finding Order

Meter on DC volts, black lead on the mains unit DC negative unless stated. Write the state (idle or live call) next to every reading.

1. Mains unit: LEDs if fitted, fuses (continuity), DC output voltage.
2. Identify the panels: lift D at the relay unit. The panel that loses its DC (D to C at the panel drops to about 0V) is on that terminal.
3. At the panel block: D to C and E to C, idle and during a call. A healthy panel read about 3V on D to C and about 8V on E to C. A failed old board read about 0.2 to 0.8V on D to C and about 0V on E to C.
4. AC millivolts across D and C while someone speaks at the panel. A jump means the microphone is working.
5. Compare panel, junction box and relay unit in the same state. A gap of volts means a bad joint, a cable fault or a panel loading the line.
6. Cable check, isolated: end-to-end ohms per core. Around 1.7 to 2.7 ohm is fine. Open or tens of ohms means a bad joint.
7. Isolation test: lift D and E at the panel. If the voltage returns to the junction box level, the panel is loading the line. If not, the fault is before the panel.
8. Relay unit: does it click on a call, and does L join the calling D (about 0V between them in a call)?
9. Speaker: measure ohms. A good 45 ohm speaker reads about 43 ohm. Open circuit means it has failed.
10. Last, swap the amplifier board. It includes the microphone.

Reference readings

These are indicative, not a specification.

Spot a Dead Board by Eye

Compare the old board with a new one. On a failed Ver 4 board the resistors R4, R5 and R6 and the transistor Q2 next to them were:

• Dull grey or brown solder
• Tan ceramic end caps exposed on the resistors
• Dirt and cobweb on Q2

A new board has bright silver solder fillets and clean legs. If you see the first set, fit a new board rather than testing individual parts.

Replacing the Door Board

1. Photograph the terminals and speaker and microphone connections first.
2. Isolate. Wire D, C and E to the new board by label.
3. Speaker leads to the L/S tabs. The new board comes with its microphone on a twisted lead.
4. Check the foam gasket around the speaker rim. Replace it if it is missing.
5. Test with a live call: D to C about 3V, E to C about 8V, then check audio from several flats.
6. Replace the speaker (92-LS70, 45 ohm, 70mm) only if it measures open circuit.

Weatherproofing

Both boards in the second job failed with visible damp damage, and the rear panel back box was rusted with loose twisted joints. Dry the box, reterminate in sealed connectors, seal the panel edge and cable entry, and leave the microphone holes and panel drain gaps open. A thin coat of acrylic conformal lacquer on the new board helps; mask the microphone, speaker, terminals and tabs first.

Parts

The 10ETXAMP is not a drop-in replacement. It has four terminals (+ - E D) and needs a 12V DC feed.

Supplier: Entryphone, 020 8870 8635, entryphone.co.uk.

Checklist

• Photograph every panel, the mains unit, the relay unit and any wiring sheet on site
• Identify which relay terminals belong to which panel
• Mains unit fuses and DC output
• D to C and E to C at the panel, idle and in a call
• AC millivolts across D and C while someone speaks at the panel
• Cable ohms per core and the joints in the back box
• Speaker ohms (about 43) and foam gasket
• Inspect the old board for R4, R5, R6 and Q2 damage
• Swap the board only after the above