HEUER Chronosplit Repair and Modules

ESA 900.231 Module and Repair

The idea for the Rawsar H4 module came to me a couple of years ago when a customer asked me to repair a Heuer Verona.


The Verona exhibited the erratic behaviour I discussed on the last page. After a lot of searching and research, I did manage to find a NOS module to repair the watch but it struck me how difficult it was to source a good reliable replacement.


I also have bought a fair few used ESA 900.231 (Chrono) and ESA  900.911 (Alarm) modules online and all of them have similar problems, time for a new module I thought.


The Rawsar H4 took me around a year to develop and get right as it is the smallest module I have designed and built and I thought the H3 was difficult!


As per the original ESA Y2 900.231 movement, the Rawsar H4 module drives both the LCD and Analogue parts of the host watch, it also functions in the same way as the original except for some minor differences outlined below in H4 Design.


H4 Design


The Rawsar H4 module is designed around a small but powerful microcontroller that is mounted on a 4-layer gold-plated PCB. The use of a microcontroller allows a lot of flexibility and replicates the functionality of the ESA module but it comes at a cost, power consumption.


Micro-controllers normally need large amounts of power to function however they can be put into a deep sleep and run essential tasks like keeping and driving an always-on LCD display. Whilst asleep a microcontroller uses very small amounts of power, the H4 utilises this deep sleep mode to keep power consumption to a minimum thus allowing the batteries to last up to a year if used sparingly.


Because time mode uses such low power the H4 has been designed and programmed to bias towards time mode as much as possible and it achieves this by:


  • If Second/Date is selected the H4 will revert to time after 10 minutes
  • The lower colon does not flash in time mode
  • If the Chrono is selected and not started or previously stopped it will revert to time after 10 minutes
  • When the Chrono is started it will run for 1 hour and then return to time however it will continue to run in the background for 24 hours.
  • If the Chrono is left to run when it gets to 24 hours it will automatically stop, reset to 00:00 and return to time mode.
  • The Chrono can be recalled at any time by pushing the LHS pusher but will revert to time every elapsed Chrono hour whilst the Chrono is running.
  • When in setting mode the H4 will revert to time after 12 seconds if no button is pushed except when it is in minute setting mode.
  • In minute setting mode, the H4 will continuously wait for a set/time synchronisation command by pushing the LHS button. DO NOT LEAVE THE H4 IN THIS CONDITION FOR LONG PERIODS as it will quickly drain the batteries.
  • If either of you pushers gets jammed in the batteries will drain quickly because the microcontroller wakes up and will draw a lot of power. Please ensure your pushers work properly and don’t get jammed.



I am delighted to announce that after extensive testing I can now offer repairs to watches based on the ESA 900.231 module using my H4 module. I have had a lot of interest in supplying modules but currently, I am only offering repairs to your whole watch using my H4 module. By repairing your whole watch I can ensure that the H4 module both fits and functions correctly, this also minimises problems. The starting price for a Rawsar H4 conversion is $475 Australian dollars plus postage. More pricing information can be found in the faults section.


The Rawsar H4 repairs should suit the following watches:




Heuer MEMPHIS 371.303

Heuer Verona 371.213*

Heuer Verona 371.215*

Heuer Carrera Twin 371.253

Heuer Carrera Twin 371.255

Heuer Diver 980.024

Heuer Diver 980.027


*Heuer also produced an alarm version of the Verona.


Breitling Navitimer 2100  Pluton

Breitling Navitimer 2300 Jupiter

Breitling Navitimer 2400 Cosmos


Chronosport UDT Sea Quartz 8109

Scubapro 200


If you are interested in a H4 conversion please email support@rawsar.com


Some examples of my work can be found on my Instagram page



The Rawsar H4 Repair Process:


The first step is to send me some pictures of your watch so I can check that you have an ESA 900-231 module fitted to your watch. If possible send some pictures of the rear of your watch with the case-back removed.


Once I receive your pictures and results I will ask you if you want to proceed with a repair and send you shipping details of how to get your watch to me here in Sydney, Australia.


When I receive your watch I will let you know it has arrived I’ll l then examine it and repeat the checks outlined in the faults section. I will also look for obvious problems like corrosion, damaged coils, damaged spacer ring etc. I will also check your LCD panel in my test jig. I will then report back to you if there are problems or additional work is required.


If no additional work or parts are required the next step is removing the old ESA electronics and LCD panel and inspecting the ESA green carrier that forms a chassis for the ESA 900-231 module. The green carrier can sometimes form micro-cracks under the LCD panel. If there are cracks evident I will discuss them with you as the carrier may need replacing which will mean a strip down of your watch and module. In most cases the green carrier is OK and I will proceed to the next step.


In the next step, I clean your original ESA LCD panel to fit a new elastomeric zebra strip and fit a prebuilt (lovingly hand built by me) Rawsar H4 module. I then fit some test batteries, at this stage, your watch should back to life. If it doesn’t I sometimes have to recheck some of the previous stages and tests.


Once the watch is running I set up the quartz Crystal oscillator with an accurate frequency counter.


I set the time and check your watch for accuracy over several days. I also ensure that the functions, time setting and pushers work correctly.


At this point, I will advise you that your watch is working and inform you that I’m testing it.


Once I’m happy that your watch is working and is accurate I will raise an invoice.

Fig 1. The Rawsar H4 module.

Fig 2. A repaired Breitling Navitimer 2300 utilising the Rawsar H4 module.

A demonstration video of the Rawsar H4 repair module:

Another video of  the H4 fitted to a Breitling Navitimer 2100 can be found on the H4 instruction page here