Hitachi CPT2125SF/DU TV raster scan line thinning and repair method of rolling fault wave type -Service Manual Download|Circuit Download|Download Drawings|schematic download|route map download|free download user manual

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Hitachi CPT2125SF/DU TV raster scan line thinning and repair method of rolling fault wave type

Time：2014-07-27 08:52:59 Source：Network Author：Unknown Clicks：1719

2.7

Measured value after repair

0

12

26

1

0

25.8

2.4

Remove the C689, found that the nominal value of 102 or 102 pf. Increase capacity or replacement is void, the failure root cause is not C689, restore the original C689. Next on C681 a 2700 pf ceramics capacitors in parallel, the lower part of the grating serious edge, the edge up, grating to about two-thirds of grating jitter, scan line density change sharply, stripes and a flyback lines appear. This machine disassembling C681 is laborious, so give up removed check C681 this step. The rest of the resistance capacity of a check, after large ado not found the problem, and replaced IC681, result failure phenomenon remains. Calm down and reflect on repair process, all related components removed checked or substitution, C681 not only remove the check, will issue on C681? Determined to put C681 break down, a look at the nominal value of 510 pf, not drawings marked with 2700 p.

On the welding on the back of a 1000 pf capacitor, fault phenomenon disappeared! That the original fault phenomenon is C681 caused loss of capacity.

Why, then, in the case of C681 originally lost capacity, and after a 2700 p on ceramics capacitor failure phenomenon not only, instead of improving the emergence of a new failure phenomenon?

In order to figure out this problem, do the following test: the actual capacity of C681 separately to 330 p, 470 p, 5 lop, 1000 p, 1500 p, 2200 p, 2700 p, 3000 p and 3300 p, are normal when under 3000 p. Then C681 decreases gradually from 330 p to 120 p in this case, the original fault phenomenon began to appear, will C681 will appear at the bottom of the grating open up, like a edge, the grating jitter, scan line stripes was rapid changes in the density and the fault phenomenon. Continue to experiment, in the original lost capacity C68l and 2700 p on ceramics capacitors phenomenon, sometimes appear in the boot, boot is normal sometimes. According to the above experiment came to the conclusion that the maximum of machine C681 should be around 3300 pf. Fault in this case the original C681 capacity, capacity of around 120 pf, and, after a 2700 pf ceramics capacitors on error because of the ceramics capacitors and the actual value is greater than the nominal value, set error is 20%, the actual capacity is about 3240 p 2700 p capacitance, such C681 location of the actual total capacity of about 3380 p, more than 3300 pf, thus appeared the above phenomenon, cause I go a lot of detours.

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