Further Notes

Disassembly Procedure

Access to the PCB requires careful disassembly of the enclosure. The process is straightforward but requires a Torx screwdriver as well as a standard Phillips head. Take care with the LED connector — it is the only step that requires a little finesse.

1. Disconnect the unit from the mains supply and remove all telephone line and extension cables.
2. Unclip the cable cover on the rear of the unit.
3. Remove the 2 black Phillips screws along the bottom edge of the case.
4. Carefully turn the unit over and remove the 3 Torx screws along the top edge of the case.
5. Carefully lift the front cover away slightly — do not pull it fully clear yet.
6. Locate and disconnect the LED connector from the PCB. This allows the front cover to be fully removed.
7. Remove the self-tapping screws securing the PCB to the rear case.
8. Remove the mains cable clamp screws.
9. The entire PCB assembly can now be lifted clear of the rear case.

General Observations

Build quality

For a late-1990s small-business telephone system, the Ultimate 106 is well built. The PCB is clean, the layout logical, and the use of a single large board rather than interconnected sub-boards is sensible for reliability. The transformer is a robust toroidal-style unit rated at 45W, more than adequate for the load.

Age-related component risk

Units of this age (25+ years) should be treated with some caution regarding electrolytic capacitors throughout the board, not just in the ringing generator. If undertaking a repair, it is worth visually inspecting all electrolytics for signs of doming, leakage, or discolouration. The high-voltage capacitors in the power supply section deserve particular attention.

Extension ringing — MOC3021 triacs

Each extension is served by a MOC3021 optoisolated triac driver. These are reliable components but can be damaged if the ringing generator has been operating with uncontrolled voltage (as occurs when R20 fails open circuit). If, after replacing C22 and R20, individual extensions still fail to ring while others work correctly, a failed MOC3021 on the affected extension is a likely cause.

The HT48R50A-0 MCU

The 8-bit Holtek HT48R50A-0 microcontroller manages the extension interface and ringing selection. It gates the individual MOC3021 triacs to select which extension is rung. This is a simple, effective design — the MCU itself is unlikely to be a cause of ringing failure unless the ringing generator supply fault has caused a latch-up condition, which would be cleared by power cycling the unit.

If You Have the Same Fault

If you have arrived here because your Ultimate 106 powers up normally but extensions will not ring, the steps to resolve the fault are:

1. Confirm the symptom — calls connect, voice works, but the telephone bell/ringer does not sound on any extension.
2. Disassemble the unit following the procedure above.
3. Locate the ringing generator area (bottom right of the PCB as oriented in the photograph on the Hardware page).
4. Visually inspect C22 (47µF 200V) for a domed or bulged top — this will confirm the fault.
5. Replace C22 with a new 47µF 200V electrolytic of the same or higher voltage rating.
6. Inspect R20 for heat damage and discolouration. If damaged, replace with a 150KΩ resistor rated at 1W or 2W for improved longevity.
7. Reassemble and test.