Seiko 7A38 - by the numbers

I am looking for an advice if and how to solve second sweep and 1/10s hand problem.

Usually (not always) second hand stays still for a few seconds after chrono is started. Not sure about 1/10s- it is hard to notice. After a reset one or both hands don't return to 0 and I need to calibrate them. And this goes on and on. 

The question how difficult would be the repair? And where is the problem?

Thanks

Jonas

Jonas.

In my experience, the delay in chronograph hands moving off their marks after the start button is pushed (and hence not subsequently re-setting to Zero) can be attributed to one or two factors. Your watch is having difficulty ....

1) Overcoming internal electrical resistance.

2) Overcoming excessive mechanical drag.

As an electrical engineer, you'll understand that there's an increase in current drawn, when the chronograph is started.

Firstly check the cleanliness of battery contacts and if in any doubt as to its condition, fit a fresh good quality battery.

Next, I'd carefully check the cleanliness of the respective switch lever contacts and if there is any trace of rust, clean it.

Same applies especially to the tiny metal contact posts embedded in the '710' plastic insulator, which make the circuit.

Lastly I'd check for any track damage on the PCB itself, particularly near the resistor adjacent to the negative contact.

The most obvious cause of mechanical drag on the sweep second hand is a displaced finger tension spring. Assuming you've eliminated that, then you're possibly looking at 'Old Sticky Oil' syndrome. The only real solution to that is a complete strip, clean and re-lubrication of the movement. But if you're lucky, regular repeated use of the chronograph function may help overcome it and provide a temporary respite.

Jonas, what I do in this situation is pull the stem out to the reset position, press the pusher and hold it in - to spin the hand around a dozen or so times. I will also warm up the watch before doing this.  

That's assuming 'Old Sticky Oil' syndrome is the cause of problem, Don.  It's not always the case. 

Thanks guys.

My observations so far:

The tension spring is in place.

I put a fresh Seizaiken battery in immediately I had the watch in my hands. The battery contacts look clean, no rust.

Sticky oil sounds like a most probable cause - chrono works properly when using continuously. I'll try to keep the watch on my wrist longer and see if that makes less problems. Also I noticed slight movements of the second sweep hand back and forth before it starts spinning.

Your watch needs a service, it's a very common issue. No big deal and usually solved by partially stripping the movement. Send me a PM.