Repair of Mingxuan MS-A55DL without reset

Mingxuan MS-A55DL did not reset, but replaced Q43, Q44, Q47 and R1807 together, and reset normally.

Machine plate No.: Mingxuan MS-A55DL

Fault phenomenon: no reset

Maintenance process: get the machine, test on the maintenance platform, do not reset.The results showed that all VCC were normal, amd board was not reset,VCC was normal, generally, Sb was checked first_Pwrok VCC is a good signal, but it is difficult to find this signal without drawings on the second and third line boards.

Repair of Mingxuan MS-A55DL without reset Figure 1 .

However, this signal is mostly affected bytriodeTherefore, it is necessary to repair this kind of fault and blind scan the whole board of triode.After taking a little time to scan the triode, no obvious fault was found. After disassembling the CPU fan and CPU BTB connector, it was found that there were several MOSFET below, which were blocked. After careful scanning, the fault points were found. Although the fault performance was not very obvious, it felt that there was a fault.

Repair of Mingxuan MS-A55DL without reset Figure 2 .

First of all, it was found that the two triodes, Q43 and q47, were not normal (as shown in the figure above). Both Q43 and q47 B poles had VCC, which could not be pulled low.So we changed Q43 and q47 together. The Q43 C pole still had 1.5V or so. We used tweezers to connect q43c pole to ground short-circuit, and reset the detection card.When r1807 was taken out for measurement, it was only more than 500 ohm. The Q44 and r1807 were replaced together, and the r1807 was replaced with a 10k resistor. The q43c pole can be pulled down and reset normally.

Repair of Mingxuan MS-A55DL without reset Figure 3 .