Using transistor tester to increase the function of high voltage package in-circuit measurement

　　If you want to add the high-voltage package in-circuit measurement function, K in the figure below is the reverse pressure test button VBR, Rl, Q1, Ll, L2 to form a self-excited oscillation circuit, Dl, D2, D3 and Cl, C2, C3, C4, C5, C6 to form a voltage doubler rectifier circuit, and D4 is the rectifier circuit of the secondary coil L4. When the secondary is unloaded, the output voltage across L4 is tested to be 250Vp-p, and the frequency is about 5000 Hz. The sum of the output voltages of L3 and L4 is greater than 400 Vp-p.

　　Modification method: Since the voltage across L4 is medium voltage, the current is small, and the sum of the output voltages of L3 and L4 is greater than 400

　　Vp-p, although the current is not large, but from a safety perspective, the two ends of L4 are selected as the output ends of the pulse signal, and two wires with alligator clips are led out as test signal lines.

　　The test method is as follows: Disconnect any end of the primary of the "high-voltage package" and unplug the tailstock at the same time (the purpose is to disconnect the filament winding, because the filament voltage is very low, which is equivalent to a short circuit in the secondary load of the "high-voltage package" for the tester). Clamp the tester signal lead clamp to the primary of the "high-voltage package" and press the reverse pressure test button VBR. If there is no short circuit inside the "high-voltage package" and no short circuit in the external load, the test instrument needle will deflect (as long as it deflects). If the needle does not deflect, it means that there is a short circuit inside or outside the "high-voltage package". You can use the multimeter R×1kΩ resistance range, the red test lead is grounded, and the black test lead is used to test the "high-voltage package" respectively.

　　The cathode of the secondary 180V, 12V, 26V and other rectifier diodes can roughly determine whether several "secondary" power supply circuits are short-circuited. If the needle indicates a certain resistance value, it can be determined that the "high-voltage package" is short-circuited internally, and the "high-voltage package" can be removed for further open-circuit testing to confirm.

　　illustrate:

　　(1) All test processes should be carried out without power to the host, otherwise, personal safety accidents may occur or the fault may be aggravated.

　　(2) The tester can measure any switching power supply and any line scanning circuit, so it is useful for VCD, DVD, monitor, copier, video recorder, etc.

　　(3) As for the interlayer short circuit of the "high-voltage package", it can be easily checked with a multimeter, so this improvement does not test the interlayer short circuit and cannot test it.

　　(4) When the tester is connected to the "high voltage package" for testing, the self-oscillation frequency of the tester will become higher, about 41.667kHz, and the voltage will be 110Vp-p.

　　This is caused by the parallel connection of the primary inductance of the "high-voltage package" and the secondary inductance of the tester and the increase in load, and does not affect the test results.