Broken Fluke 52 II Thermocouple Thermometer

[dencohe]

Hi Guys,


I recently acquired a broken Fluke 52 II thermocouple thermometer. The symptoms include no reading from either channel (T1 or T2). I decided to go ahead and open the unit and inspect. I found a cracked ceramic capacitor but no other signs of damage. I used forum member TiN's guide at https://www.eevblog.com/forum/testgear/fluke-5x-ii-series-thermometer-tear-down-and-hacks/ to replace all the front-end components. The meter still did not read any voltage on either of the channels, so I went ahead and just replaced all the active components up until the ADC (LT2400). It now reads voltages and the open contact comparator is causing readings to happen when a voltage appears at the channel. The ADC is still not seeing the correct voltage, regardless of where the mux'es are switching.

My theory so far that someone touched two exposed non grounded themocouple wires across some unknown voltage potential and destroyed most of the meter although there is no physical signs of anything wrong besides that cracked ceramic cap. I am looking for anyone who has any advice or someone who may have a better understanding of how the circuit works.

Thanks,
Denver