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UMF 28-40


UMF 28-40UMF 28-40


The UMF Ruhla caliber 28-40 is a true quarz movement with stepper motor, and hence not a target of this collection, but its unusual construction saved it a place here:

movement without electronics boardmovement without electronics board

As you easily see, the 1978 launched caliber 28 bases on most parts of the several million times produced caliber 24. The modification for quarz driving was relatively moderate: At the place of the mainspring barrel, a large Battery of type LR 44 was set as powering source, and instead of the escapement works with escapement and balance, a rather large stepper motor was used. The rest of the movement remained more or less the same, even the center second hand was indirectly driven, just like on caliber 24. This constrution is pretty unusual and rare for a quarz movement.

Overlay of caliber 24 and 28Overlay of caliber 24 and 28

Electronics was already quite advanced at the end of the seventies, so this movement only uses a tiny quarz, an integrated circuit and a trimmer condensator for regulating the quarz. This construction was so timeless, that even today, modern quarz movement are built the same way, except, that on most modern movement, the costly trimmer condensator is already lacking.

electronics boardelectronics board

The electronics board was pretty large and therefor had to be placed besides the actual movement. The new plastic board, which was then required blows up the size of the new movement to giant 14 1/2 lignes, which are almost 33mm. By now it's clear, why this movement had to be replaced soon by a true (small), newly developed quarz movement.

downside of the electronics boarddownside of the electronics board

However, the usage of an integrated circuit shows a general Problem: When, e.g. by drowning water, the circuit goes out of order, especially after many years, it's no longer possible to repair the movement, since no replacement parts (replacment ICs) are available.

UMF 28-40 dial sideUMF 28-40 dial side

On the dial side, you see the familiar construction, known from the UMF 24-33, with its very simple date mechanism in plastics, the date disc spring and the rocking bar winding mechnism. On that mechanism, the now useless top gear is removed.

dial side without date discdial side without date disc




 Technical data

Number of jewels0
Movement constructionEscapement wheel, Fourth wheel, Third wheel, Center wheel
Winding mechanismyoke
Setting lever spring2 holes
FunctionsHour, minute, second, day, quartz controlled
Beats per hour3600
UMF 28-40UMFUMF28-4014 1/2''''''UMF 28-400 Jewels, 14 1/2'''''', 3600 A/h, SCI,QG



Usage gallery

Ruhla Quarz 32768 gents watchRuhla Quarz 32768 gents watch