Watch the second boot, relay suck up vocalist. Measurement on instantaneous output voltage has a + B, then relay release, + B voltage disappeared. Relay and off when the phone is switched on, and then release, suspected to be a protection circuit starts, the microprocessor the standby protection action. Measure the C point voltage protection circuit, the boot to low level, measure the point B voltage protection circuit in the boot into high level instantly, thus judgment is triode Q854 caused by the protection. Due to point B external multiple protection detection circuit, adopt the method of measuring various protection circuit isolation diode voltage determine the scope of the fault.
 
 
When measuring + B over-current detection circuit isolation diodes D859 when the anode voltage, as a high level. Measuring D859 voltage on both ends is forward biased, so when is a + B caused by over current detection circuit protection.
 
In order to determine the line is the output short circuit caused by the over current protection circuit, or a + B over-current detection circuit element metamorphism caused by error protection, USES the disconnect D859, remove + B over-current protection method. Boot measurement + B voltage on the low side, 144 v to around IOOV, as that of a normal grating, brightness is reduced, measuring line level output current is controlled in 1 a, line output tube heating. Measuring line output circuit of resistance within the normal range, estimation is line output transformer or deflection coil exists partial open circuit fault, causing the output over-current protection + B. Change after the line output transformer, voltage + B and grating returned to normal, restore protection circuit D859 also no longer protection, troubleshooting.