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• The XYTRONIC 988D is calibrated with the two front-panel “CAL” ports, not through a hidden button sequence.
• Warm the station, set a reference temperature, measure the real tip temperature with a certified thermometer, then turn the trimmer in the corresponding port (clockwise to raise, counter-clockwise to lower) until the display matches the measured value.
• Repeat separately for the soldering iron and for the desoldering gun; each has its own port.
Station architecture
• 988D is a dual-channel, micro-controller-based unit. The MCU reads the tip thermocouple, drives the heater with a PID algorithm and shows the calculated temperature on the LED display.
• The display can be off by a few-tens of degrees because of component tolerances and sensor ageing.
• XYTRONIC therefore brings the calibration trimmer (a 10 kΩ multi-turn pot on the controller board) to the front panel as a “calibration hole/port”, one per channel. Turning the pot adds/subtracts an analogue offset to the thermocouple signal; the firmware simply shows the corrected value.
Why no “secret menu”?
– Unlike later LF-988D + or LF-2000 series stations, the 988D does not store a digital offset in EEPROM. The only reliable way to calibrate it is the physical pot described in the datasheet (Jameco part #156814, XYtronic catalogue 302, p. 10).
Calibration accuracy targets
• Production and rework: ± 5 °C (± 9 °F) at 350 °C.
• General hobby use: ± 10 °C acceptable.
• If you need IPC-J-STD-001 class 3 compliance, document three points (250 °C, 350 °C, 420 °C).
Recommended measuring equipment
• Dedicated tip thermometer (Hakko FG-100/101B, Tenma 72-10840, or Metcal STTC checker).
• Type-K micro-bead thermocouple with 1 mm bead is acceptable if a tip thermometer is unavailable, but expect ± 5 °C additional uncertainty.
• Multimeters with 3 mm ceramic-bead thermocouples are not suitable (thermal loading error 20-40 °C).
Step-by-step procedure
a) Preparation
– Install the tip/nozzle you use most; clean and tin it.
– Place the station in a draught-free area; ambient 20 – 25 °C.
– Power ON and wait 10 min for thermal equilibrium.
b) Select set-point
– 350 °C (662 °F) for Sn-Pb work, or 380 °C for lead-free.
c) Measure actual temperature
– Touch the thermocouple to the tinned tip; wait for reading to stabilise (< 3 s with FG-100).
d) Adjust
– Insert a 2 mm Phillips or 1.5 mm flat-blade screwdriver through the “CAL” port of the active channel.
– If measured < display, turn clockwise slowly; if measured > display, turn anti-clockwise.
– Re-measure after 10 s; repeat until within desired tolerance.
e) Verify at a second point
– Change set-point to 250 °C; wait 3 min; re-check. Small residual error (< 5 °C) is normal.
– Document date, tip, instrument serial number, final offsets.
Typical trim range & warnings
• Factory ships roughly centred; ± 40 °C of adjustment is available.
• Do not force the pot beyond its end-stop; the wiper can break and the MCU will see open-circuit → “HHH” or “LLL”.
• If adjustment is exhausted yet error persists > ± 50 °C, suspect:
– Failed tip sensor (thermocouple open/short).
– Heater cartridge ageing.
– Main-board op-amp U1 drift (rare).
• Newer XYTRONIC LF-988D + and XYTRONIC LF-2000 series moved to digital, menu-based calibration; the procedure in some online videos (SET+DOWN = “CAL”) applies to those models, not the original 988D.
• Industry trend is toward auto-calibration using built-in temperature profiling (e.g., JBC with TID station) and tip-ID chips; the 988D predates these features.
• Thermocouple offset math: The pot injects a small DC voltage into the INA (≈ 0–40 mV) corresponding to ~0–40 °C at the K-type sensitivity of 41 µV / °C, giving the ± 40 °C range.
• Analogy: Think of it as zeroing a scale—move the needle until the reading matches the known weight.
• Calibration is maintenance; it does not void warranty.
• For ISO 9001/ESD-controlled production lines, maintain calibration records and use instruments traceable to NIST or equivalent.
• Avoid tip temperatures above 450 °C to reduce rosin fume generation (health hazard).
• Re-check every 6 months, or after changing heating element.
• Mark the pots with a paint dot after calibration to detect tampering.
• Store frequently used tips in a nitrogen holder to slow oxidation and reduce calibration drift.
• Some early 988 (non-D) units do not have front calibration holes; the pot is on the PCB— same procedure, but you must open the case (unplug mains first!).
• Button-based “CAL” instructions found on the internet refer to LF-988D + (touch-screen) or LF-2000; applying them to 988D will do nothing.
• Investigate replacing the analogue pot with a digital trim IC (e.g., AD5161) and adding firmware support—community mod on EEVblog link [10].
• Study tip-ID EEPROM concept (PACE TD-100, JBC C245 smart-tips) for automatic calibration.
The XYTRONIC 988D’s temperature accuracy is tuned via physical trimmers accessible through the two labelled “CAL” ports. Warm the unit, measure the real tip/nozzle temperature with a calibrated instrument, and turn the corresponding trimmer until the display matches reality. No secret key sequence is involved. Periodic recalibration, correct measuring tools, and good tip maintenance keep the station within ±5 °C of set-point, ensuring reliable soldering results.
