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This field output IC failure phenomenon is a typical expression of sealing off the pin . Richard Field output block IC451 (LA7837) pin has been re- welded before. The fault has been repaired several others , and replaced IC451. But the fault remains. Most part of the Ministry related field scanning devices have had traces of heavy welding machine inside view . Vibration test circuit boards, without a corresponding change in the failure phenomenon , the possibility of poor contact element initially ruled out .Kspservice manual download site
The machine uses a field output IC has a separate treatment field scanning feature, which with small signal processing circuit IC601 does not exist AC and DC negative feedback , but must provide the field excitation pulses between the IC60131 feet (TA8844N). Measurement when a fault occurs IC451 voltage output 12 feet , with the beating and dramatic changes in the grating , measuring its drive voltage inputs ¢Ú feet equally unstable voltmeter pointer kept swinging between 2V ~ 4V scale. Charles IC451 24V supply voltage is normal.Kspservice manual download site
About the circuit shown in Figure l IC451 ¢Ú feet and legs IC60131 between . IC60131 pin output field by the excitation pulse , after Q403 inverted added to IC451 ¢Ú feet. S601 for the maintenance switch during normal operation S601 fixed point ¢Ü in N position , D601 positive terminal voltage is short-circuited , D601 deadline . When in maintenance adjustment of status , S601 placed S position , then IC451 ¢Ú pin is shorted , the output stage stops working farm , horizontal bright line appears on the screen . Meanwhile , 12V voltage by R620, D601 added IC60153 feet, CRT reduced by IC601 control the brightness level to avoid too bright bright lines on the CRT damage .Kspservice manual download site
Since there is no negative feedback between the DC IC451 and IC601, the voltage output of the field variation will not significantly affect the voltage variation of the signal portion of the input voltage changes IC451 but it will significantly affect the voltage at its output . Therefore, to determine a fault on the circuit between the pin and IC451 ¢Ú IC60131 foot .
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