Boot after observed phenomenon, the screen is not bright, one of the indicator on a regular flashing (about 3 seconds), at the same time accompanied by relay suck up vocalist repeatedly. 7Ncservice manual download site
 7Ncservice manual download site
Teardown measurement of switch power supply output + 50 v, 70 v +, + 13 v, and + 7-10 v v voltage are normal. Test manager Q404, secondary power tube Q402 IC301 and field output circuit, found no apparent short circuit phenomenon. Analysis of degaussing relay is influenced by computer block IC201 (M - CUKL07) control, according to the judging degaussing relay has repeatedly suck up vocalist, unnerve IC201 work may be a reason, unable to normal boot signal output. 7Ncservice manual download site
 7Ncservice manual download site
 7Ncservice manual download site
As shown in figure, first check IC201 attending feet of + 5 v power supply voltage is normal, IC20113, 14 feet crystals of peripheral circuit and 18 feet outside the reset circuit (not painted) has not found the problem. Measure voltage IC201 degaussing control (4) feet wide fluctuations between 0 ~ 4.5 V regularly, and IC201 most other pin voltage with regular fluctuations. Doubt is the destruction of data in memory, with the new memory write data after the computer test, fault is still. Tests found that IC201 bus output voltage in o. SCL 41 feet 8 ~ 1.8 V, SDA 42 feet between 1.2 ~ 4.6 V voltage fluctuations, multimeter pointer in the swing as well as a wide range of very irregular dithering phenomenon, and normal is commonly 4 to 8 V constant. The two feet often directly affect the work state of IC201 voltage is not straight. Because many voltage deviation from the normal range, decided to first lC201 41 feet peripheral circuit to check up. In order to quickly determine the scope of the fault, respectively will scan circuit IC401 (STV6888) (3) feet and visual circuitry ICl02 (LMl246) of 12 feet away from the SCL bus circuit and electric commissioning failure remains. But when the author from the motherboard in the tube end SCL fuses disconnect test, if the display appears the high pressure and the supply is normal (light) at this time. Computer to test piece IC201 41 and 42 feet voltage is normal. Carefully check, found that the board is put in apparent edge and a small 6.2 V voltage regulator tube ZDl03 in (see figure 1) even on SCL pathways, measured with a hollow needle down, found that it has serious leakage close to the short circuit. With good tube replacement after electrify of commissioning, fault immediately ruled out.

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