Source Heater Error: Timeout

Hi All,

We have a 5977 MSD which came up with two errors following a site power outage:

"Source Heater Error: Timeout - temperature fails to increase under full power."
"Analyser Heater Error: Timeout - temperature fails to increase under full power."

We've seen something similar before and needed to replace the fuses inside the left compartment but I've checked and these appear to be OK (they look OK and they test for continuity on a meter). I checked the main fuses on the back too for the sake of being thorough but the MS powers up OK and they're also good. I also checked both the source heater and the quad heater's for continuity too and they both ready OK. I'm not sure what kind of resistance to expect on the temperature sensors but all the wiring looks OK. 

Is it possible the left side fuses look and test OK but are still damaged? Likewise for the heater cartridge for the source? Or, is it more likely to be the main board... (eeek!)

Any help would be greatly appreciated.


  • The source and analyzer heaters, the wires with the beads on them, disconnected from the white ceramic source connector board should Ohm out at 14 or 15 Ohms.  They must be open to ground.

    The source and analyzer PRT (Platinum Resistance Thermometers), disconnected from the white ceramic source connector board, should Ohm out at ~109 Ohms at room temperature.  The resistance goes up with heat, so if it is already warm the resistance will be higher. 

    Also check the cable connections to the analyzer side board -- DO NOT unplug or plug them in to the board with the power on!!!  That will damage the instrument.

  • Thanks I'd say my thermocouple resistance for the source was definitely too low - more like 14 Ohm for that. Would a fault there prevent both zones from heating though? That's the puzzle I'm stuck on tbh. 

  • Absolutely!  If the PRT is 14 Ω instead of ~109 Ω, the system thinks the source is, oh, negative 340 degrees (joking guess), and when the heater turns on and the resistance does not change it thinks something is wrong and shuts off the heaters, both of them, for safety. If it did not, the heater could run away without control and then things get melty.

  • Brilliant! This is super helpful . Thanks for this. I'll double check that thermocouple but that makes sense.

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