Simplex Master Clock with design fault

Discussion in 'Electric Horology' started by dennishoy, Mar 29, 2017.

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  1. dennishoy

    dennishoy Registered User

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    #1 dennishoy, Mar 29, 2017
    Last edited: Mar 29, 2017
    Good evening folks,

    I recently obtained a Simplex master clock "type 946-2 Op" from a local auction house here in the UK.
    Externally, it seemed to be of good quality, but upon closer inspection I was disappointed.

    The internal movement was a cheap, quartz type with plastic gears as fitted to budget clocks for the home in the late 1970s.
    This was fitted between a pair of pressed aluminium plates with thin, pressed brass gears running in plastic bushes pushed into the plates.

    Turning my attention to the electronics, I noticed badly-placed components on the circuit board and removed the latter for closer inspection.
    There were numerous poor-quality soldered joints so I re-soldered the complete board, pressing on the components to make them flush with the board and clipping the protruding tails short on the underside.

    It was then I noticed a glaring design error.
    Those of you who know some electronics will be familiar with zener diodes as voltage regulating devices. These require a series resistor to limit the current flowing through the device, but in this case, the 33 V diode was connected directly across the main reservoir capacitor with no resistor. Not surprisingly, the diode had overheated and gone open circuit which put around 50 Volts on the series regulator and taken that out too. Thankfully the transformer survived even though the 3.15A secondary fuse had no chance of blowing when the transformer could only deliver 250mA.

    I thoroughly checked the board and there was never a place for the series resistor and have posted pictures showing the diode Z1 connected directly across capacitor C1. I have since modified the board and added the necessary series resistor (last picture).

    I also noticed that instead of the normal rechargeable battery used on many master clocks during power fails, a large electrolytic capacitor had been fitted. This would have been useless as a backup during power fail as it would only have held the circuit for a few seconds. There is no charging circuit on the board, just a huge (computer grade) electrolytic capacitor whose inrush of current when initially charging might blow the underrated 1A bridge rectifier.

    I had assumed that Simplex was a quality manufacturer, but was wrong in this case as there are design faults and sloppy manufacturing.

    My query is to ask if anybody else has seen this type of clock before (type 946-2 Op) and wondered how long it would have lasted before failing.

    Perhaps it was a prototype for testing before going into the manufacturing process for market?

    Any thoughts please as I'm a bit puzzled?
    Were Simplex a quality manufacturer at this time?

    Thanks.
     

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  2. harold bain

    harold bain Registered User
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    Is what you show all you have?? Never heard of that model number. As far as I know the 943 master was the last one before they went all electronic in the early 80's with the 2350 series. Nothing you show looks particularly like a Simplex product.
     
  3. dennishoy

    dennishoy Registered User

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    Sorry, I should have posted some pictures of the complete clock.
    I've temporarily put it back together so here's more pictures.

    The brand label indicates it is a Simplex clock and the other label shows it as a model 946-2.
    Quite a pleasant 80's design looking at it, but as we say in England, you should never judge a book by it's cover. 300280.jpg 300281.jpg 300282.jpg 300283.jpg
     
  4. harold bain

    harold bain Registered User
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    I don't think this model ever showed up in North America, at least I never saw it when I worked for Simplex up to 1980.
     
  5. George Nelson

    George Nelson Registered User
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    Hi, All,

    My limited electronic experience points me to this being a low-volume model, due to both the design of the circuit board and the associated connectors. My experience is all from the US- perhaps in the UK things are a bit different.

    George Nelson
     
  6. caperace

    caperace Registered User

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    In the early 80's Simplex sold their first time Calculator the ETC it was made and tested in Germany for 3 years before it was released in the States, it was a quality and reliable machine, simplex also sold Watchmen's Clocks, that were made in West Germany in 1960's, all quality products. I think this must have been a prototype, it has the Simplex ID and decals, but lacks the quality that would be found in a product that they sold, and quality mattered.
     
  7. dennishoy

    dennishoy Registered User

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    #7 dennishoy, Mar 31, 2017
    Last edited: Mar 31, 2017
    Thank you all for your thoughts. I agree that it is probably a prototype for the reasons given above.

    I have further thoughts to back up that idea. Firstly, why would a production model have a combination of screw terminal connectors and edge connector?The edge connector is used where a repair is effected by a simple change of circuit board, thereby reducing 'down time'. The screw terminal connector negates this idea. Most of the pcb edge connector pads are not connected and there are 4 x yellow wires going nowhere in the loom to the movement.

    The badly-placed holes drilled in the pcb appear to be hand-drilled and are not in a straight line and components do not line up neatly. A factory production board would be drilled using a jig.

    The use of a 6800uF capacitor instead of battery backup would simply not work for more than a few seconds.
    There is no charging circuit on the board for a battery, or D.C. connector for an external battery.

    I've traced out the circuit and apart from the missing current limiting resistor, I have noticed that the logic seems over complicated as though other functions could be added later.

    The clock utilises a mass-produced movement that I have seen in cheap carriage clocks from that time. This uses a three-phase stepper motor to rotate the seconds hand one-sixtieth of a turn for each step (i.e. 60 steps = one minute). There will be the familiar one second click-click-click once I get ti running again.
    There is a plastic cam on the output shaft that (couple with a weight) closes a pair of contacts for a few seconds once every minute.

    The one-minute pulses are applied to logic to clean them up and drive a latch and bistable. The bistable drives a pair of relays using transistors, where either one relay or the other is switched (never both at once). The output of the relays drive the slave clocks, but unless I have missed something, these will be bi-polar pulses very minute so a 120 second slave clock will be needed. I think this may be another error by the electronic design engineer(s) at Simplex.

    There is a free-running astable (oscillator) which can be gated into the circuit using the seconds/minute switch so that the slave clocks can be driven at 1 second rather than 1 minute when adjusting the time.

    I think this was maybe an abandoned project because Harold says they went all electronic in the 1980s.
    I'm quite interested in making this work correctly as a 'fun' project.

    I've posted a few more pictures of the quartz part that drives the rest of the movement. The circuit board forms one side of the assembly with a white, plastic moulding forming the other side. The electronics are sandwiched between the two and a plastic output gear drives the metal wheels in the rest of the movement. I can't see this lasting very long under 24/7 use. I've also posted a picture of the contact arrangement that provides a 60 second pulse for the rest of the clock. The rest of the movement uses plastic bushes as bearings (see second picture). The first picture shows the contact arrangement to provide a pulse every 60 seconds to drive the electronics. Second picture shows the white plastic bushes. 300428.jpg 300429.jpg 300430.jpg 300431.jpg 300432.jpg
     

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