Tudor 79170 accurate except....

[iclick]

My Tudor 79170 Big Block chrono was serviced last year immediately after purchase and since then has been generally very accurate and consistent, around 1-2 sec/day fast, as long as I'm wearing it. When off my wrist it is inconsistent and always runs slow regardless of the resting position, anywhere from -4 to -27 in varying positions on my Timegrapher with amplitude often showing often in the low to mid 200s, but stays around 250° when warm. Room temperature has been 68-75° lately.

I assume this is a temperature issue, so what is the cause? My other BB chrono with an identical movement is much more consistent across these temperature ranges.

[iclick]

Nobody has a clue?

[floridamike]

I doubt its temperature, temperature can effect timekeeping but not amplitude that much until you reach temps way lower then 68 . When its on your wrist constantly being wound its at "full wind" and the mainspring is giving the train the most power. However once off the wrist, the mainspring is winding down and the amplitude is dropping rapidly, likely due to a ever weakening mainspring. Sadly on a 7750 to swap a mainspring means taking the watch apart almost fully.

To test this, let the watch sit and go down to room temp, them pick up the watch and quickly manually wind it until you believe its at full wind and put the watch on the tester. My guess is you will observe a low error and a decent amplitude.

[iclick]

FloridaMike, thanks for your input. After reading your reply I removed the watch from the safe, gave it 40 winds (CW only), and put it on the Timegrapher. I then wore it for an hour in the same environment to warm it up and did another set of readings. The ambient temperature is 78° at this time.

When the watch was serviced last year the watchmaker replaced the mainspring and barrel. The original barrel had a flaw that kept the mainspring from winding fully.

(Position - Variance - Amplitude)

[kanikune]

I would suggest you repeat that test by first winding the watch until you hear the mainspring to slip. That makes sure you have full wind in your first measures.
7750 has long mainspring, not sure if 40 is enough.

Saying this because seems like full power was reached while wearing it, not in the initial winding.

[iclick]

I don't think the initial winding is a factor since this behavior happens when it is worn consistently with no manual winds in between. The variance seems related only to the temperature of the watch.