Test equipment radiation survey meters

Ludlum 3: troubleshooting and error codes

The ServiceForge knowledge base holds 6 documented symptoms for the Ludlum 3, with 17 ranked causes, 18 diagnostic checks with test points and expected values, and 0 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Meter goes full scale or pegs out radiation

Meter needle deflects to full scale or maximum reading and does not respond normally to changes in radiation level

Ranked causes

1. Detector cable failure causing excessive noise (common)
2. High voltage setting incorrect (common)
3. Loose or broken internal wires (occasional)
4. Instrument can installed backwards causing speaker interference (occasional)

First check

Test with replacement detector cable

Test point: Detector cable connection
Expected: Full-scale deflection should resolve if old cable was faulty

4 more checks with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

No power or meter does not reach BAT TEST or BAT OK mark

Unit fails to power on or battery test indicator does not display expected marks on meter face

Ranked causes

1. Weak or dead batteries (common)
2. Batteries installed backwards (common)
3. Battery contact corrosion or contamination (common)
4. Loose or broken internal wires (occasional)

First check

Verify battery voltage is sufficient

Test point: Battery terminals
Expected: Sufficient voltage (weak batteries indicate low voltage)

3 more checks with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Nonlinear readings

Meter display shows nonlinear response or erratic readings across measurement range

Ranked causes

1. Incorrect high voltage setting (common)
2. Noise in detector cable (common)
3. Sticky meter movement (occasional)
4. Meter zero offset (occasional)

First check

Measure high voltage output

Test point: HV output
Expected: Voltage per calibration certificate or detector manual (typically 900 Vdc for GM tubes, 460-550 Vdc for peanut tubes)

3 more checks with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

No audio output

Speaker does not produce audio clicks or tone when radiation is detected or during operation

Ranked causes

1. Audio ON-OFF switch in OFF position (common)
2. Loose or disconnected speaker connector (common)

First check

Verify audio switch position

Test point: Front panel AUD ON-OFF switch
Expected: Switch in ON position

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

No response to radiation radiation

Meter does not respond to radiation source; no counting activity or meter movement when radiation is present

Ranked causes

1. Detector not responding or failed detector (common)
2. Incorrect operating voltage for detector (common)

First check

Test with known-good detector and cable

Test point: Detector connection and output
Expected: Meter should respond to radiation source with known-good detector

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Exposure rate or CPM high voltage

Adjust calibration controls on front of instrument using screwdriver to set two calibration points per scale

Ranked causes

1. Calibration adjustment required (common)

First check

Verify calibration points span adequate range

Test point: Calibration control settings
Expected: Two points separated by at least 40% of full-scale value, approximately equidistant from mid-point (e.g. 25%/75% or 20%/80%)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Community

0 fixes logged by technicians through their AI, with outcomes, for this model.

ServiceForge knowledge base record. Field-unverified unless technicians confirmed it. A teaching summary of the record, not a service manual. Export 2026-10-14.