The LS6500's Year 2021/1921 Date Rollover: What It Means for Decay-Corrected Data

If your Beckman Coulter LS6500 has been printing dates in the 1920s since 2021, this isn't a glitch you can fix with a reboot. It's a real-time clock limitation, and it affects any decay-corrected measurement the instrument runs. Here's what's happening and what it means for your counting program.

What's Going On

The LS6500's clock stores the year as a two-digit field with a fixed range that stops at 2020. Once the calendar passed that point, the clock wrapped back 100 years instead of moving forward, so it reports 1921 instead of 2021. The count data itself is fine — it's the date stamp attached to it that's wrong.

This is easy to miss during routine use because it doesn't show up when you set the date. An operator can type in the correct year at the setup screen and the instrument will accept it. But once an Automatic Count runs, the clock reverts to the wrapped date, and every report from that run, including any decay correction the instrument applies, is stamped with 1921 instead of the actual date.

Why It Affects Decay Correction

The instrument's automatic decay correction depends on the elapsed time between a reference date and the count date, based on the isotope's half-life. If the clock is wrong by roughly a century, that elapsed-time calculation is wrong too.

For isotopes with long half-lives, the effect on the final number may be small. For shorter-lived isotopes, tritium is a common example, the error can be large enough to matter if you're relying on the instrument's built-in correction without checking it independently. If your lab uses decay-corrected DPM for dose calculations, effluent monitoring, or waste characterization, it's worth flagging this to your RSO as a known limitation of the instrument, so it can be accounted for however makes sense for your program.

Why There's No Software Fix

Beckman Coulter discontinued the LS6500 before this issue came up, so no firmware update was ever released to fix it. Labs have generally handled it in a few ways:

• Pulling raw CPM/DPM values and calculating decay correction separately, using the real acquisition date.

• Sending the RS-232 output to a separate system that timestamps the data on its own.

• Keeping a note on file explaining the date offset for anyone reviewing the raw printouts later.

These work, but they add manual steps to something that's supposed to be automatic.

The Actual Fix

This is a hardware limitation, not a software bug. Fixing it means swapping a small set of components on the main board that control the clock's date range. Once that's done, the LS6500 handles current dates correctly on its own, including during Automatic Count runs, and you don't need any of the workarounds above.

The kit is compatible with instruments running firmware versions 29.0 and 27.9, and extends correct date handling through 2040.

If you'd like help with this, Service AI can do the installation on-site. The work is documented, and it's fully reversible if that's ever needed.

If you have an experienced field technician on staff who's comfortable working inside the instrument, we can also just supply the kit and walk your team through it.

Get in Touch

Need parts, technical assistance, or an engineer on-site for your LS6500? Service AI specializes in keeping discontinued Beckman Coulter instruments running. We stock parts, perform calibration and adjustment, and can supply recertified replacement instruments. Contact us at support@serviceai.us or call +1 (510) 899-1340.

Visit serviceai.us for our full inventory of recertified Beckman Coulter and Agilent laboratory instrumentation.

How to Leak Test the Cs-137 Source in Your Liquid Scintillation Counter

A practical guide to wipe testing and interpreting results for tabletop LS counters.

Why This Test Matters

Beckman LS counters use an internal ~30 µCi Cs-137 sealed source as an external standard for quench monitoring — including H-number calculation. On instruments from the LS 5000 and LS 6000/6500 series manufactured before January 1994, this source used an early pellet/matrix encapsulation design. Over extended operational lifespans, these suffered mechanical degradation and seal deterioration, causing microscopic leaks that showed up as rising background counts (exceeding 60 CPM) and calibration failures. Beckman Coulter responded with customer advisories and free replacement programs.

The fix was a transition to doubly-encapsulated stainless steel welded sources, largely supplied by Eckert & Ziegler / Isotope Products Laboratories. These comply with ISO 9978 and ANSI sealed-source integrity standards and effectively eliminated the leakage problems of the older design.

For instruments with the modern encapsulated source, a genuine leak is unlikely — but periodic contamination checks remain good practice, and most radiation safety programs require them regardless. The wipe test takes under an hour using the LS counter itself.

Safety Requirements

Before starting, ensure the following:

• Wear rubber or plastic gloves and your radiation dosimeter.
• Follow ALARA principles — time, distance, and shielding — throughout.
• Treat all gloves and swabs as potentially contaminated until the instrument is proven clean.
• Conduct all work in compliance with your institution's radiation safety program. Notify your Facility Radiation Safety Officer (RSO) as required.

Step 1: Check Instrument Background

Set the instrument to count for 5 minutes with a wide-open window and count the sealed Background Standard. Counts should be less than 80 CPM. Higher readings suggest existing contamination in or near the counting chamber — resolve this before proceeding.

Step 2: Access the Source

1. Remove the upper panel and the two centre pieces of lead shielding.
2. Remove the two screws from the bracket holding the upper source tube.
3. Manually slide the source spring upward until the source just protrudes from the end of the tube.

Do not remove the source from the spring. This limits your exposure by avoiding direct handling of the source.

Step 3: Prepare Reference and Source Swabs

• Reference swab: Place a clean swab or Q-tip (tip only) into a clean vial half-filled with scintillation cocktail. Label it "Reference."
• Source swab: Wipe the end of the source and around the outside of the spring with a fresh swab. Place the tip into a second vial half-filled with cocktail. Label it "Source."

Step 4: Program and Count

Set up the LS counter as follows:

Parameter	Setting
Counting Time	10.0 minutes
Isotope 1 Window	0 – 300
Isotope 2 Window	300 – 1000
Isotope 3 Window	Wide open
Data Calc	CPM
H#	OFF
All other parameters	NO or OFF

Count in order: (1) sealed Background Standard, (2) Reference swab, (3) Source swab.

Step 5: Interpret Results

The source swab should read close to the reference. Swab material itself contributes 40–80 CPM, so a similar reading from the source swab is normal. A reading more than 100 CPM above background warrants action.

Pay attention to which window the counts fall in:

• 300–1000 window: Cs-137 signature — elevated counts here indicate a genuine source leak.
• 0–300 window only: Likely grease fluorescence, which can read as high as 300–400 CPM without any radioactive contamination. Not a cause for alarm on its own.

The LS 6500's Hot Graph spectral display is particularly useful here — it gives an immediate visual of where counts are falling across the energy spectrum, making it straightforward to distinguish a real leak from fluorescence interference.

If a Leak Is Detected

Stop operating the instrument immediately.

1. Carefully remove the source spring from the instrument.
2. Cut the end of the spring off and place the spring and source into the vial from the ship kit.
3. Contact your RSO immediately. Dispose of the source and all contaminated materials through your institution's radiation safety program.
4. Do not return the instrument to service until it has been inspected and cleared by a qualified service professional.

How Often to Test

Most radiation safety programs recommend leak testing:

• At least every 6 months for instruments in routine use
• After any service or access to the source assembly
• After any incident — unusual counts, a drop, or suspected contamination
• Before returning an idle instrument to service

Real-World Example: What a Leaking Source Looks Like

The printout below is from an actual wipe test on an LS 6500 with a leaking source. Five samples were counted — the results tell the story clearly.

Samples 1 and 2 are clean — the sealed Background Standard reads 33.00 CPM in Window 2 (300–1000), and the reference swab reads 33.50 CPM. Both are normal baselines. Samples 3, 4 and 5 are swabs from the leaking source: Window 2 readings of 883.00, 445.40 and 513.60 CPM respectively — 13 to 26 times the reference level. The signal is unambiguous and entirely in the Cs-137 window (300–1000), confirming genuine radioactive contamination rather than grease fluorescence.

The Hot Graph below shows the sample spectrum for the leaking source swab. Note how all counts cluster above the 0.30K dashed line — squarely in the Cs-137 energy range. This spectral signature is what a leaking source looks like on the LS 6500's Hot Graph display, and why it is such a useful diagnostic tool for distinguishing a real leak from lower-window interference.

Summary Checklist

• Background under 80 CPM before starting
• Gloves and dosimeter on
• Source spring kept in place — do not remove source
• Reference swab prepared before wiping source
• 10-minute count across all three windows
• Flag source swab readings more than 100 CPM above background
• Distinguish Cs-137 counts (300–1000) from grease fluorescence (0–300)
• Contact RSO immediately if leak detected
• Document and retain all results

Questions about your LS counter or source assembly? The Service AI team includes factory-trained engineers with deep experience across the Beckman Coulter LS line. Reach us at support@serviceai.us or call +1 (510) 899-1340.

Visit serviceai.us for our full inventory of recertified Beckman Coulter and Agilent laboratory instrumentation.

Beckman LS6500: A Troubleshooting Guide for Elevator Jams

Are you experiencing an issue with your Beckman LS6500 where the rack, especially the mini (blue) rack, is not stopping at the correct position, thereby causing the elevator to jam up?

This can occur when the instrument incorrectly identifies the mini (blue) rack as a maxi (standard white) rack and attempts to move the vial up into the detector.

When such a problem arises, it is most likely that the mini rack is not being correctly identified by the Mini/Maxi sensor board.

The Mini/Maxi sensor board (Beckman P/N. 500726) is only installed on LS6500 models that have the versa-rack option. It is very unlikely that your LS6500 counter does not have this option.

Most often, when this sensor board malfunctions, it fails to recognize the mini rack, which causes the instrument to misalign the rack, thereby causing the elevator to jam up. Under such circumstances, users will also notice that they do not experience elevator jam issues when they are using Maxi (standard white) racks on the instrument.

For more information, contact our technical support line at +1-510-899-1340 or email us at support@serviceai.us.

website: www.serviceai.us

How can one perform AC and DC voltage checks on a Beckman LS6500 Mains Power Supply (PN. 606682) module?

Check the video below to learn how to test the voltage output(s) (+5 VDC, +15 VDC, -15 VDC, and +24 VDC) of the Beckman LS6500 power supply module.

This video demonstrates the AC and DC voltage checks on a new style power supply module outside the LS6500 instrument. The same process applies when measuring voltage with the new or old style power supply module mounted inside the LS6500. If the LEDs on the relay board piggybacked on the power supply module (not shown in this video) are all OFF, it is a clear indication that the power supply module is dead.

My Beckman Coulter LS6500 CRT monitor is dead. Is there a replacement available?

Yes, there is a replacement available, and a good one too!

Our LS6500 READY! Wyse Winterm terminal module is configured to work with Beckman Coulter LS6500 liquid scintillation counters and is the perfect replacement for the obsolete CRT terminals that were originally shipped with the LS6500. The fully tested plug and play module also works with Beckman LS6000 instruments with serial number 7064XXXX or higher and is available at the Service AI webstore. The LS6500 READY! Wyse module ships with a power supply adapter and a cable to connect with the LS6500. Email us at support@serviceai.us, or call us at our technical support line at +1-510-899-1340 for more information.

Installation tips:

Installing the Wyse module for your Beckman Coulter LS6500 is a breeze! This plug-and-play device simply replaces your existing CRT terminal. To get started, remove the old terminal and connect the Wyse Winterm module to the same CRT 25 pin port using the 25/9 pin cable that ships with the module.

Next, connect any available LCD flat screen monitor to the Wyse module using a standard VGA cable (not included in the shipment).

Once the physical connections are complete, it's important to ensure that the Wyse Winterm module is powered on (using the included power adapter) before the LS6500 is powered on and booting up, just as you would with the old CRT terminal.

For more information or assistance with installation, please email us at support@serviceai.us or call our technical support line at +1-510-899-1340.

LS6500 READY! Wyse Winterm Start-up Screen

website: www.serviceai.us; email: support@serviceai.us; technical support: +1-510-899-1340