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Resolving the error related “Incorrect Voltage at MCRL pin”. During the process of programming the MCRL pin is used to deliver the high-voltage programming pulse (around 13 Vp-p). The programmer board has a charge-pump inverter circuit that generates this high voltage from the 5volt supply voltage. Furthermore, to ensure the correct programming voltage, the programmer employs a feed back circuit that verifies the programming voltage via its A/D converter circuits. When one of these circuits fails to operate correctly, it reports the “Incorrect voltage at MCRL pin” error. Usually there are three major reasons for this fault. 1. Faulty charge-pump circuit or the high voltage regulator 2. Incorrect sense voltage in the feed-back circuit 3. Incorrect reference voltage for feedback A/D converter An initial estimate of the fault can be made by looking at the VPP voltage as seen by the MPLAB software. First connect the circuit to a computer in the usual way. Set the development mode to MPLAB ICD to open the programming dialog window. Then click on the “Options” button to open the advanced programming option dialog. The charge-pump circuit operates only when it is requested by the MPLAB software. The simplest method to start this circuit is to click on the “Update” button in the advanced programming options dialog. Click on the update button and observe the reading that appears for the VPP on the advanced programming options dialog. VPP reading Less than 7V 12.8V – 14.8V 16V – 18V 22V and above Faulty circuit Faulty charge-pump circuit. No fault. Incorrect reference voltage at A/D converter Incorrect sense voltage in feedback circuit Testing for Charge-Pump Circuit. 1. Connect an oscilloscope to TP21 on programmer board. Click on the update button and observe the voltage. If the charge-pump inverter is operational you should see a reading around 18V on the oscilloscope. If not check the components L1, R28, D4 and Q4 2. Next is to check the high voltage regulator. Connect the oscilloscope to TP13 and then click on the update button. If the regulator is operational you should a read a value around 13V. Otherwise check U3, Q4 and Q3. Checking for the Sense voltage in feed back circuit (this can be done only when the charge pump circuit is operational) 1. Connect the oscilloscope to Pin 3 of U2 and click on the Update button. If the voltage is correct you should observe a reading around 1.1V. If the reading is above 1.3V, change R22 with a 10K resistor. Testing for the Correct Reference voltage for A/D converter. 1. Using an accurate multi-meter measure the voltage at pin 5 of U2. The reading should be close to 2.06 Volts. However, in some circuits you may read a value less than 1.90V. This if often due the LED drawing a larger correct and thus the problem can be corrected by adding an additional resistor in series with the LED. You may compute the value of this additional resistance as follows: 2.06 Vref R5 Rnew Vcc Vref where Vref is the voltage at pin5 of U2 and Vcc is the voltage at pin 20 of U2. The nominal value of R5 is 330Ohms (however it is advisable to remove the resistor form the circuit and then to measure its exact value using a multi-meter. Usually the value for new resistor (Rnew) should be between 9 – 16 ohms. You may round this to the nearest available value. 2. The new resistance should appear in series with the LED. Break the connection between + terminal of the LED and R36 (on the solder side) of the PCB. Then solder the new resistor instead of this connection.