I have it set to internal trigger but the output discrepancy is the same when triggered from my TG501A Time Mark Generator.
If I set the Time Mark Generator to 0.1us and the Ramp Generator to 1us, I don't see the expected 10 time marks per one ramp, which is what initially alerted me to this fault.
I re-set the relevant trimpots to half scale and ran through the ranges with the front dial set to '1' and output amplitude to max (output should be 10V P-P)
Range - Output - Output Amplitude
10us - 5.7us - 4.4V
100us - 30.6us - 3.2V
1ms - 250us - 2.7V
10ms - 1.8ms - 2.1V
100ms - 24.6ms - 2.7V
1s - 163ms - 1.9V
I checked all the voltages into the Sweep Control and Miller Integrator, and they seem to agree with the schematic.
Also the front panel Gate Output coincides perfectly with the ramp output, which comes straight from the Sweep Control chip via a couple transistors.