Wow, a very general question!
There are so many things other than a wash. First as in the medical profession, do no harm an a vinegar wash can harm. Number two, the watch is over 45 years old and the history of repair is unknown. You never know what the previous owner did. I have seen these covered in WD40 and other products!
Are you familiar with a multi tester or a continuity tester?
All electronics out there were washed prior to sale. The term wash for me refers dipping a soft artist brush and in the solution then work it into the module and AT ALL TIMES, AVOIDING the LED block. Rinse the same way. Always avoid the LED block as contaminants can work there way into, under and on the LED lens which may leave a residue that cannot be removed. On some modules the LED is not sealed and wire bonds are exposed.
1 wash with warm soapy water solution first to remove any oily contamination.
2 Rinse with water.
3 wash with white vinegar the same manner.
4 rinse with water.
5 wash with anhydrous alcohol. That is alcohol with a very low water content.
6 rinse with water.
7 air dry or dry with hairdryer on low.
8 apply an electronic contact enhancer such as deoxit.
I use deoxit contact cleaner and enhancer. Apply sparingly with fine tipped paint brush to contacts and exposed electronics. Also at the main controlling IC BUT DO NOT TOUCH ANY WIRE BONDS if they are exposed!
A wash with vinegar is a last resort and typically works if there is a visible trace of corrosion from battery leakage. It can however remove the remnants of a circuit trace causing a failure. That is, under the corrosion precipitate (copper sulfphate) the trace may be connected by a partially remaining bit of trace which the vinegar removes causing a break in the circuit. Some battery corrosion is caused by out gassing of the batteries and results in corroded ICs internally. These modules look pristine but will never work. So do the wash last, do the next list first.
After a cursory scan; are the contacts clean, top and bottom. Does it look like the module has been interfered with? Does a good magnet illicit any response? Before removing the module, remove the case back.
Clean the contacts,
Magnifying glass, check with pictures on the web, are all components present.
Any signs of previous attempts at repair, sloppy solder joints.
Heat the module with hair dry until JUST hot to touch.
Reinstall batteries.
Try with good magnet.
Did the heat bring it to life?
If yes, did it stay functional?
If yes, did it die when cooled?
If no check:
- magnetic read switch function. Lift the module to your ear, apply the magnet, did you here a faint click?
- If you have continuity tester, check the continuity of the magnetic read switch with and without the magnet.
- any obvious connections that appear to be broken.
- quartz crystal, replace. Your decision here, do this before the wash or after, if a wash does not help.
- consider new after market replacement if for personal use. If for resale, inform the buyer
There are more sophisticated checks but they would rely on circuit design expertise and equipment. Try the above first. Of course if it is still dead, then a last ditch attempt with a vinegar soak.
Good luck!
Geoff
P.S. I see now that you have a semi response. Follow the above procedures. When the oscillator is bad, a few things can happen:
1 the display does not work.
2 the display comes on with a single digit that changes eveytime the batteries are removed and replaced. This simulates a timing signal.
3 the time keeping functions are out to lunch, there is a display but extremely inaccurate.
All do these point to a bad quartz crystal.