When you’ll actually need this. The detector gain pots are factory-set and rarely touched. There are two cases where you will touch them:
  1. After a hardware swap. Replacing a detector assembly or a preamp board in the field shifts the detector’s electrical baseline; the manual gain reset re-establishes a starting point that Auto Cal can then fine-tune.
  2. Recovering a drifted detector on an older unit. Detectors slowly drift over years of operation. If a detector has drifted far enough that the built-in Automatic Calibration can no longer pull it back into range, a manual gain re-set can sometimes recover it. Not guaranteed — if the detector is too far gone, it’s too far gone — but this is the first thing to try before spending on a replacement detector. We’ve had customers save the cost of a new detector this way; we’ve also had customers confirm a detector was beyond saving. Either answer is useful.

The Multi-Wiper and the Genesys Genii share the same Genesys-platform calibration architecture. The keystrokes, menu paths, and gain-pot adjustment procedure are identical on both instruments — on multi-well configurations. Single-well units don’t need this procedure: manual gain adjustment exists to match detectors to each other, and there’s nothing to match against on a one-detector system. Auto Cal alone is the right tool there.

If you’ve never opened the chassis on a Genesys-platform counter before, this is a service-level procedure — the gain pots are physically located inside the unit, accessed through the chassis cover, and adjusted with a small screwdriver. Standard service-tech precautions apply.

What you’ll need

  • A calibration source. Either of these works — use whichever your lab already has on hand:
    • Co-57 — reference peak at 122 keV. Common in labs that already use Co-57 for routine calibration.
    • Cs-137 — reference peak at 662 keV. Procedure is identical; only the marker value changes.
    Either a single source (move it well to well) or a matched set sized to your well count.
  • The Factory Calibration password. The password for current firmware (v4.0 or later) is 5421123. Same on the Multi-Wiper and the Genii.
  • Access to the gain-pot adjustment screws. One per well, accessed through the chassis. Pot-to-well mapping depends on configuration — see Step 5 below.
  • A small flat-blade screwdriver sized for the gain pots.
  • About 5–10 minutes per well once you’re inside the menus.

Step 1 — Set up the system

  1. Insert the Co-57 source(s) into the detector well(s) you’re going to adjust.
  2. From the Main Menu, navigate to Diagnostics: press 7#.
  3. Select Factory Calibration: press 5#.
  4. A password dialog appears. Enter 5421123.

Step 2 — Reset gain to a known starting point

Before touching the pots, reset the firmware-side gain values for every well to a known value. That gives the manual adjustment a clean baseline to work from.

  1. From the Factory Calibration menu, select #3 — Enter Cal Parameters.
  2. Change the gain on every well to 512.
  3. Do not change the values for HV volts, ZERO, or LLD. Those are factory-set per detector; leave them alone.
  4. Return to the Factory Calibration menu.
Why 512? The gain field is a 10-bit value (range 0–1023). 512 is the midpoint, which gives you headroom in either direction once you start turning the physical pot. The actual final value will land wherever the spectrum aligns to the marker; 512 is just the starting line.

Step 3 — Enter Manual Calibration mode

  1. From the Factory Calibration menu, select #1 — Manual Calibration.
  2. Type *6. This opens the manual gain-adjust workspace.
  3. Select Well 1 to start.

Step 4 — Set the marker to your source’s photopeak

The marker (a vertical reference line on the spectrum display) tells you exactly where the photopeak should land. Set it to the energy of whichever source you’re using:

  1. Type *4 to enter the marker-adjustment dialog.
  2. Set marker <keV> to the right value for your source:
    • Co-57 → 122
    • Cs-137 → 662

With the source already in the well, the spectrum will start accumulating immediately. You’ll see the photopeak forming somewhere in the display — almost certainly not on the marker, since the gain is sitting at the 512 baseline and not the value the detector actually wants.

Step 5 — Adjust the physical gain pot to align the peak

This is the actual manual-calibration step. You’re looking at the spectrum on the display, identifying where the photopeak has settled, and turning the corresponding gain pot to slide the peak left or right until it lines up with the marker.

Direction of adjustment:

  • Peak is to the LEFT of the marker → gain is too low. Turn the pot clockwise to increase gain.
  • Peak is to the RIGHT of the marker → gain is too high. Turn the pot counter-clockwise to decrease gain.

Pot-to-well mapping (this changes with configuration)

The pot layout depends on how many wells your unit has. There are two layouts:

2-, 3-, 4-, and 5-well units — single preamp board. Pots run in a single row, in order. The leftmost pot is Well 1; the next is Well 2; and so on across.

6-, 8-, and 10-well units — two preamp boards. Wells are split between two preamps:

  • LEFT preamp = ODD-numbered wells (1, 3, 5, 7, 9)
  • RIGHT preamp = EVEN-numbered wells (2, 4, 6, 8, 10)

So on a 10-well unit the left preamp carries the pots for wells 1, 3, 5, 7, and 9, and the right preamp carries pots for 2, 4, 6, 8, and 10. Don’t assume left-to-right order — always confirm by adjusting one pot a small amount and watching which well’s spectrum responds. If the wrong spectrum changes, you have the wrong pot, and you’ll learn the layout in 30 seconds.

One pot at a time. Whichever configuration you have, only adjust the pot for the well you’ve currently selected on the display. Touching pots while a different well is selected just disorients the procedure — you’re moving a peak you can’t see.

Step 6 — Use the spectrum-window controls

While viewing the isotope spectrum you have a small command menu to control the display. Press the * key to access the menu window. Useful keys:

  • 1 — RUN toggle. Tap to start or stop count accumulation. When RUN is highlighted, the system is accumulating counts.
  • 2 — CLEAR (tap) resets the spectrum to zero so the next adjustment shows from a clean baseline. HOLD 2 changes the high-voltage on the selected detector (the digital adjust described in the callout above).

The recommended rhythm is: turn the pot a small amount → clear the spectrum → let it accumulate for a few seconds → observe where the peak landed → turn the pot again. Repeat until the peak is centered on the marker. Remember: there’s no on-screen feedback during the pot turn itself — the clear-and-observe cycle is the only way to see what the pot did.

The pot adjustment is invisible to the firmware. Turning the gain pot does not change the VOLTS readout, and there’s nothing on the display that says "you just turned a pot." The Genii has no way to know. The only way to verify a pot adjustment took effect is to clear the spectrum and watch where the peak lands on the next accumulation. Turn → clear → wait → observe → adjust again. That’s the rhythm.
The 2 key is the digital voltage adjust — separate from the pot. Holding the 2 key changes the high-voltage on the selected detector, which does show on the VOLTS readout (bottom-right of the screen) and shifts the spectrum peak. Direction is set by the + / − indicator in the upper-right corner of the display: + raises the voltage (peak shifts right); toggling to − lowers it. This is independent of the pot — both the pot and the 2 key influence the spectrum peak position, but only the 2 key shows up on the VOLTS readout. For most manual cal work the pot is the primary tool; the 2 key is for fine-tuning the HV when you need it.

Step 7 — Repeat for every well that needs adjustment

Select the next well via the well-selection key, repeat Steps 4–6 for that well’s pot, and continue through all wells in the configuration.

You don’t need to land the peak perfectly on the marker by hand. Get it close — within a channel or two — and the built-in Automatic Calibration routine will do the final precision matching in the next step.

Step 8 — Exit and run Automatic Calibration

When all detectors look reasonably aligned:

  1. Exit Factory Calibration mode (back out through the menus).
  2. From the Main Menu go to the Calibration Menu.
  3. Select #3 — Gain Adjust to run the automatic calibration routine.

Automatic Calibration takes the rough manual alignment you just did and fine-tunes it to spec — setting the precise high-voltage, locking in the LLD, and balancing gain across detectors. After it completes, the unit is back in normal operating condition and ready for routine work.

If something doesn’t look right

  • The peak isn’t moving when you turn the pot. First, confirm you’re actually turning the right pot — on 6/8/10-well units the pots are split between two preamps (LEFT = odd wells, RIGHT = even wells), so the pot at "physical position N" doesn’t necessarily correspond to "Well N." Adjust a pot a small amount and watch which well’s spectrum responds. If nothing moves on any well, make sure you reset the firmware gain value to 512 in Step 2 — without that reset, the firmware may be applying a value that completely overshadows the pot range.
  • You can’t get the peak into the display range, even at full pot rotation. Confirm the source is actually in the well, the source is the isotope you set the marker for (Co-57 = 122 keV, Cs-137 = 662 keV), and that you didn’t accidentally change HV volts, ZERO, or LLD in Step 2. If you’re trying to recover a drifted detector on an older unit and the peak still won’t come into range: the detector is probably beyond saving via gain adjustment alone. Time to spec a replacement.
  • Automatic Calibration fails after manual adjustment. The most common cause is one well being too far off from the others to balance against. Re-enter manual mode and check the spectrum on each well; bring any outliers closer to center, then re-run Auto Cal.
  • You don’t see a Diagnostics or Factory Calibration menu option. The menu structure described here is for firmware v4.0 or later. Earlier firmware uses a slightly different menu path; contact LTI service if you’re on older firmware.

Cheat sheet (printable)

  • When: after detector or preamp swap; or to recover a drifted detector on an older unit before replacement. Multi-well units only — single-well units don’t need this.
  • Sources: Co-57 (marker = 122 keV) or Cs-137 (marker = 662 keV) — whichever you have on hand
  • Menu path: Main Menu → Diagnostics (7#) → Factory Calibration (5#) → password 5421123
  • Reset firmware gain: Enter Cal Parameters (#3) → gain 512 on every well, leave HV/ZERO/LLD alone
  • Manual Cal: Manual Calibration (#1) → *6
  • Marker: *4 → 122 (Co-57) or 662 (Cs-137)
  • Spectrum controls: * opens menu → tap 1 = RUN toggle, tap 2 = CLEAR spectrum, hold 2 = adjust HV (direction set by + / − in upper-right of display)
  • Pot adjustments are invisible to the firmware — only way to verify is to clear the spectrum and watch the peak position on the next accumulation
  • Pot direction: peak too LEFT = clockwise (more gain); peak too RIGHT = counter-clockwise (less gain)
  • Pot → well mapping:
    • 2/3/4/5-well: single preamp, pots in well order left-to-right
    • 6/8/10-well: LEFT preamp = ODD wells (1,3,5,7,9); RIGHT preamp = EVEN wells (2,4,6,8,10)
  • Finish: Exit Factory Cal → Calibration Menu → Gain Adjust (#3) for Auto Cal

Further reading