Siemens Hemodialysis Electronic PCB Board Reworking can be seen that the appearance of each component is normal, and the resistance of each component is measured in turn.
The forward resistance of LED1 is about 30KJ, the forward resistance of D34-36 is about 6Kft, the forward and reverse resistances of voltage regulators Z14, Z16 and triode Q4 are normal, and the op amp is normal. The resistance of the output terminals U31-7 and U31-8 to ground is the same as that of a normal circuit board, so TP48 downward is also regarded as an open circuit when analyzing the resistance of TP51 to ground, that is, the resistance at both ends of R216 (the nominal value is only 7.87Kft). Three-pole output during normal operation.
When the comparison voltage TP50 and the divided voltages TP51 and TP49 deviate from the normal value, the input of any unit at the non-inverting terminal is lower than the inverting terminal or the difference is too small, the comparator outputs a low level or a lower voltage, and the Q4 collector voltage of 26V makes LED1 and D35 and / or D36 turn on, at the same time can not drive Z16 (10V), Q5 turn on, LED1 lights alarm, no current flows through the collector of Q5, output high level, the circuit outputs an alarm signal, the machine stops continue to start, long sound alarm.
The reverse resistance of the voltage regulator Z15 is only more than 10 Kfl. Replace the same type of voltage regulator. Due to the narrow space, it is soldered to the back of Siemens Hemodialysis Electronic PCB Board. The resistance value of R216 is 7. lKfi. Think it is back to normal. After replacement, TP51 voltage is about 4.9V normal, TP49 voltage is about 5.5V normal, the machine no longer alarms.
Summary: The voltage regulator Z15 is damaged, there is a local short circuit, the 9V DC voltage cannot be obtained normally, the machine alarms, and the current increases at the same time, causing the resistor R213 to burn out.
