Three faults, one instrument, one visit.
A Shimadzu LC-2010CHT came to us with a noisy autosampler, a pressure reading that would not settle and peak areas that changed from injection to injection. They looked like one problem. They were three.
Three complaints arrived together: autosampler errors, a pressure reading that would not settle, and peak areas that did not repeat. Each had its own cause, and each was fixed on the same visit.
A drive board replaced, a faulty gradient valve bypassed, and a plunger seal turned the right way up. Six injections afterwards overlaid cleanly.
| Autosampler noisy, X/Y errors | Autosampler drive board had failed. Replaced. |
| Pressure swinging every 1.5 to 2 minutes | Gradient valve open on all ports A to D. Bypassed, run isocratic. |
| Peak area and height not repeating | Plunger seal fitted upside down at an earlier service. Refitted. |
Fault 1: the autosampler
What we saw
The autosampler arm was loud as it moved in X and Y, and the drive voltage reaching it was not right. The error log told the same story, again and again:
SIL:NO NEEDLE HOME (X)
SIL:NO H.P.V HOME
SLIP MOTOR (X) and
NO NEEDLE HOME (X) entries: the X axis was losing steps and never found
its home position.The fix
With the mechanics moving freely by hand, the fault pointed to the board that drives the autosampler motors. We replaced it. After that the arm travelled to every position smoothly and quietly, completed its rinse, and the instrument came up to Idle with no errors.
Autosampler moving smoothly, no new errors in the log.
Fault 2: a pressure reading that would not settle
What we saw
Every 1.5 to 2 minutes the pressure reading jumped about, through values like 40, 10, 0 and 150, then came back. A pattern that regular is rarely the column.
The cause
The low-pressure gradient valve was open on all four ports, A to D, at the same time. The pump was drawing from every line at once, so whatever reached the pump head changed from moment to moment.
Gradient valve not switching: all ports open.
The fix
We took the valve out of the flow path and connected the solvent line straight to the pump's inlet check valve, running isocratic. The pressure settled at once and held within about 2 bar.
Stable pressure. The lab can run its isocratic methods now; the gradient valve is due for replacement before gradient work resumes.
Fault 3: areas and heights that would not repeat
What we saw
Retention times matched from injection to injection, but peak area and peak height did not. When retention time holds and area moves, look at how much liquid the pump really delivers and the injector really loads.
The cause
At an earlier service, by another engineer, the plunger seal had been fitted upside down and the plunger had not been seated properly. A reversed seal leaks a little on every stroke, and not by the same amount each time.
Plunger seal reversed, plunger not seated.
The fix
We refitted the seal the right way round and seated the plunger, checked the injection valve rotor seal (it was fine), and cleaned the parts in an ultrasonic bath before reassembly. Then six injections of the same standard.
All six injections overlaid cleanly: area, height and retention time together.
What this case is worth remembering for
Autosampler errors, a pressure trace with a rhythm, or areas that will not repeat are each fixable without replacing the instrument. Tell us what the error log shows and what the pressure does over five minutes, and we can usually say where to look before we arrive.
We service and calibrate Shimadzu, Waters, Agilent, PerkinElmer and Thermo systems. Call Kumar Mudaliyar on 9819424897, or WhatsApp 9819424897.