Tektronix TDS340 trigger adjustments?

[cincin]

My trusty TDS340 (with option 14) works wonderfully but for one thing: the trigger behaviour doesn't match the trigger display. That is, the trigger arrow and displayed trigger level value, are both some 600mV off where the unit actually triggers.

i.e. If I look at the 5V calibration square wave (0V to 5V), the trigger won't actually trigger until the displayed trigger value is at about 600mV, and the arrow indicating the same. And it won't stop triggering until I am about 600mV above the wave. So it'll trigger on the 5V square wave all the way up to 5.6V, with the trigger cursor arrow 600mV above the square wave.

It hasn't really gotten in the way yet, when you know you can compensate for it. But I'd love to adjust that, to make it perfect.

I read the service manual (for the TDS340A, closest I could find) and the only trim-pot based adjustment they speak of is for the incoming probe signals.

Anyone familiar with Tektronix trigger adjustments?
Or is this not adjustable, and a symptom of a potential problem?

Any insights greatly appreciated.