Defective ITS (Integrated Telephone System) Section. No handset and monitor transmission / reception:
Following the ITS section or NCU section, search for the route between the microphone and the telephone line (sending) or between the telephone line and the speaker (receiving) where the signal disappears. Check the components at that point.
NO PULSE DIALLING
NO RINGTONE / NO BELL
NO TONE DIALLING
Power Supply Board Section. Key components for troubleshooting
Check the following parts first: F1, D10-D13, C5, and Q1. This comes from our experience with experimental tests. For example: power supply and lightning surge voltage test, withstanding voltage test, intentional short circuit test, etc.
Caution: If you find a melted fuse in the unit, donot turn on the power until you locate and repair the faulty parts (except for the fuse); otherwise the fuse will melt again and you cannot pinpoint the faulty point. In most cases, the symptom is that nothing is output. It is more likely that the fault is in the primary side rather than the secondary side. Check the primary side first.
TROUBLESHOOTING FLOWCHART
Broken Parts Repair Details
(D10, D11, D12, D13).
Check for a short-circuit in terminal 4. If D10, D11,D12 and D13 are short-circuits, F1 will melt (open). In this case, replace all of the parts (D10, D11, D12, D13, F1).
(Q1)
The worst case of Q1 is a short-circuit between the Drain and Gate because damage expands to the peripheral circuit of Q1. This is due to a very high voltage through the Gate circuit which is composed of R19, Q2, and Q21 etc. You should change all of the parts listed as follows. F1, Q1, R19, Q2, Q21
(D101, D104)
If D101 and D104 are broken, the oscillation circuit in the power supply cannot operate. Check it with an electric tester.