Trouble phenomenon: main screen no picture sound black screen, hold on to a blue screen, small screen, sound analysis of normal maintenance:

1, preliminary analysis shows that primary video signal is lost, resulting in the failure. VCD AV input signal using the road, found the main screen and the small screen are normal, tentatively identified faults before the video, audio switching circuitry.
2, analysis of signal flow (pictured below):
Main picture signal from RF signal splitter into → → main screen main screen → tuner → video, audio switching circuit 3.

Maintenance:

First check the signal distributor. using method of transposition, divider output to main screen tuner and small screen tuner signal cable replacement, resulting symptoms unchanged. Description signal splitter works correctly.

Then check main picture high frequency head. through on high frequency head Terminal voltage of detection, found except main picture high frequency head of AGC voltage not normal outside, other no obviously differences. has, and no signal Shi of main picture AGC voltage are for 1.8V. and at of small picture high frequency head of AGC voltage has, and no signal Shi of voltage respectively for 4V and 7.6V. for further determine whether high frequency head has fault, will main, and small picture high frequency head for replacement. results fault phenomenon not variable, Description main screen tuner no problem. carefully check the RF AGC1 resistance-capacitance of the circuit on the motherboard components and transistors were no problem, demonstrating that no normal AGC voltage from the main scene on board or its previous CPU AGC control circuitry.

RF AGC delay adjustment. this machine RF AGC adjustment is through CPU to software form for of. Control route as figure a by shows. into software adjustment of method following: first will TV volume reduction to minimum, then by Xia "timing shut machine key", screen displayed timing shut machine symbol Hou, immediately while by Xia remote control Shang of "screen displayed key" and TV Shang of "volume reduction", stay screen displayed "CHECK1" Shi, by moving remote control Shang of digital key 2 Select adjustment project, screen displayed "RF AGC1 "Shi, note original numerical. this machine (main picture) RF AGC1 original numerical for 66, (small picture) RF AGC2 original numerical for 68. operation remote control volume added reduction can adjustment numerical size. through adjustment small picture parameter found, numerical increases, gain reduced, instead gain improve. but adjustment RF AGC1 parameter Shi, main picture no reaction, main picture high frequency head of AGC numerical also no changes. and from CPU (IC1213 of 25 feet) to in the put Board ( IC101 of 30 feet) between of RF AGC adjustment pathway and the components (R1106, and R147, and C114, and C115) are normal, and software adjustment Shi, corresponding of potential also has changes. through above check proved, in the put Board on CPU issued of RF AGC adjustment instruction no reaction, problem determine is out in has main picture in the put Board Shang. so recovery RF AGC adjustment of original numerical.

Determine fault range. the machine in the put Board used blocks type plug pulled structure, but plug Board between distance very near cannot online measurement. main picture in the put Board Shang used AN5179NK for in the put, Board Shang while and has Li sound processing function. small picture in the put Board Shang used AN5177NK do in the put. two block Board although in function Shang has differences, but carefully compared Hou found interface can compatible. so removed main picture in the put Board, with small picture in the put Board generation of, will Board Shang small picture in the put Board Jack at free. check correct Hou boot, Main picture sound normal, the fault disappears. now fully acknowledging a fault occurred on board in the main screen.

Main picture in the put Board of maintenance. removed in the put Board, reference figure II, focus check has RF AGC DELAY entered loop, RF AGC output loop, no found any problem. with new AN5179K substitution original machine IC101 AN5179NK, try machine fault cannot excluded. due to cannot online measurement, decided again removed main picture in the put Board, plus +5V power, on IC101 of DC voltage for measurement.

IC101 pin function and DC voltage in Figure II below:

Pin functions DC voltage (v) DC voltage pin function (V)1VCOGND016IFAGC2.62VCO1.517RFAGCOUT4.83VCO1.518AFCVCC4.84VCOVCC4.819MAINVCC4.85QIFDETOUT1.420VIFIN2.86AFC2.221VIFIN2.87VIFDETOUT1.822MAINGND08IF AGCIN1.723QIFIN3.09INVIN1.724QIFAGC3.710FEEDBACK1.825BIF011VIDEOOUT1.826BIF3.012AFCOUT2.127BIF3.013AFC2.728AUDIOOUT2.214AFC2.829BIFVCC4.815RFAGCDELAY2.730BIFIN2.6 tables + 5V voltage by figure II by depending on of B1 terminal of "+5V" end joined. first check IC101 (AN5179NK) of the power circuit, found 4, and 29 feet voltage for 4.8V (normal), and 18, and 19 feet voltage for 0V. from table a in the we can see IC101 of 18 feet for AFC power, 19 feet mainly power. This II feet no power IC101 certainly cannot normal work. so removed add-ins of +5V power, with digital multimeter of "pass stock" check + 5V power of the article branch. reference electric principle figure (figure II), carefully check found in Figure II by shows of a, at +5V power of pathway was truncated. the circuit board for double go line, circuit breaker of a, at is located in connection double go line of round hole Shang. the round hole was burning Hou of traces clear visible. for security side, detection has 18, and 19 feet peripheral components, and determination has the part power on to resistance, no exception Hou, avoid round hole, will circuit breaker part fly line connection. again added +5V power test, IC101 of supply voltage to return to normal, IC fever is no exception.

The main and small pictures to put plate back to its original position, power test, TV, small screen, good as new, and troubleshooting.