Hi everyone,
I was just wondering if anyone has knowledge and kindness to help me repair an aircon top up machine control board.
This unit came in and the owner described that one of the scales are no longer working. It has three scales, OIL IN, OIL OUT and refrigerant TANK. So, the refrigerant tank scale is not moving at all when checked through the menu. I've checked the scale, and it's all fine, it has its voltage supply and gives signal back into the control board. Connectors on the control board to the three scales are identical, cables are interchangeable, and I did switched them over to check scales. All three scales are working on OIL IN or OIL OUT ports. None of them show any sign of life on refrigerant tank port. This tells me that scales and their cables are all fine. The problem must be on the CIRCUIT BOARD.
The CONTROL BOARD
As far as I could reverse engineer, the incoming signal from the scales are received by TLC2652 op-amps(three of them, one for each scale input) Just before the op-amp input each line is protected with bidirectional diodes(these are not shorted and diode test shows 0.547V voltage drop across them on the DMM. These are for ESD protection as far as I can understand. The output from the op-amps are taken over by an analog to digital converter TLC3548(outputs from all three op-amps are heading to this A/D through various resistors and parallel caps) and then by a pic microcontroller which does all the magic.
Because two of the ports are working( OIL IN and OIL OUT ), the pic micro is working the A/D is working( can the A/D be defective on one input? ). I decided to desolder an op-amp from a working port(from OIL IN) and solder it in place of the defective port(TANK). This made no difference and the op-amp died(as I had no ESD protection). Soldering it back into its original place made the port to behave exactly as the TANK port, not reading the scale.
Ordered three op-amps and a set of ESD gloves and leads to ground myself and all tools, mat, soldering station,etc.
Soldering in an op-amp to the OIL IN port was a success, but the TANK port is still the same, not reading the scale.
I don't know what to check further on, hopefully I have not bored you all to death with my story.
Anyone's help/advice would be greatly appreciated.
Daniel
I was just wondering if anyone has knowledge and kindness to help me repair an aircon top up machine control board.
This unit came in and the owner described that one of the scales are no longer working. It has three scales, OIL IN, OIL OUT and refrigerant TANK. So, the refrigerant tank scale is not moving at all when checked through the menu. I've checked the scale, and it's all fine, it has its voltage supply and gives signal back into the control board. Connectors on the control board to the three scales are identical, cables are interchangeable, and I did switched them over to check scales. All three scales are working on OIL IN or OIL OUT ports. None of them show any sign of life on refrigerant tank port. This tells me that scales and their cables are all fine. The problem must be on the CIRCUIT BOARD.
The CONTROL BOARD
As far as I could reverse engineer, the incoming signal from the scales are received by TLC2652 op-amps(three of them, one for each scale input) Just before the op-amp input each line is protected with bidirectional diodes(these are not shorted and diode test shows 0.547V voltage drop across them on the DMM. These are for ESD protection as far as I can understand. The output from the op-amps are taken over by an analog to digital converter TLC3548(outputs from all three op-amps are heading to this A/D through various resistors and parallel caps) and then by a pic microcontroller which does all the magic.
Because two of the ports are working( OIL IN and OIL OUT ), the pic micro is working the A/D is working( can the A/D be defective on one input? ). I decided to desolder an op-amp from a working port(from OIL IN) and solder it in place of the defective port(TANK). This made no difference and the op-amp died(as I had no ESD protection). Soldering it back into its original place made the port to behave exactly as the TANK port, not reading the scale.
Ordered three op-amps and a set of ESD gloves and leads to ground myself and all tools, mat, soldering station,etc.
Soldering in an op-amp to the OIL IN port was a success, but the TANK port is still the same, not reading the scale.
I don't know what to check further on, hopefully I have not bored you all to death with my story.
Anyone's help/advice would be greatly appreciated.
Daniel
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