Tek AM503 is the oldest current probe amplifier and there is no LED display on the range. Mine have the PCB corrosion as in the photo. Thus I use Methanol to clean the pcb but after that it is still do not looks very clean! Anyway there are few items need to be restored.
- Note that all the old E-capacitors after checking is still working fine, no replacement !
- One light bulb is not working, the one always ON! I changed them to LEDs but after that the resistors to limit current need to add in a 1.2k resistors. Note that the light bulb is driven by Negative voltage and thus I need to re-install the polarity of LEDs! I also reverse the two wire position and thus I need to reverse the plug on the pcb to get the right light on the current switch.
- The Rotation current selection switch is a long switch covered. It has gold fingers to press on the gold plated PCBs at many locations for top and bottom side. The contacts are in pairs and either touch top or bottom side. To sort or to go through the attenuator resistors which is seated at bottom side. Since I have wash the pcb, I need to take out all the attenuator resistors to clean them one by one! There is lots of gold on this pcb and resistors or transistors!
- The last thing I do not like the design of regulator of this instrument is that there are two power transistors located at the power supply unit bottom chassis for heat sinking. The connection is through the long gold fingers slots which sometimes may give to contact issue and make the power regulator not functioning well. Thus care must be taken when plug in the module into the power supply TM501.
- Nothing wrong with the A6302 after disassembly for cleaning. Care must be taken to put back the ground contact springs and do not loss the metal bead. The current transformer is also be handle carefully.
