+photos 59th minute synchronous wall clock master clock simplex 3510 14 seconds


Senior Member

I have to assist in repair Simplex Clock System.
Not my area of expert...

Need some help understanding the general principles and then weak links.
My limited understanding of the system is that
There was a master clock that used to trigger a corrective pulse at 3510 hz.
This has been displaced by an Andover EMS.
Here are some photos.

So, briefly, the clock [or ems] pulls in two relays, one after the other.
First the generator is made to run and then the clock correct signal is injected into the 480v line. A DC signal on the generator field windings. This "noise" has to get around the transformers, so it is coupled down to the 110v line. There are two solenoids in each clock and when it gets a 8s pulse, the first solenoid gets the minutes to pull up to the top and a 14s pulse gets the second solenoid to get the hands to 6 o'clock.

Then signal wires have to leave the master clock and get to other buildings which have other generators. Some buildings don't have generators, apparently just the coupling devices... The three vacuum tube boxes.

Why the schematic seems so complicated to me?
There are three 3p relays, one for the generator, one for the 3510 pulse and seems like the 6000 is not used?
Two relays would fulfill my limited understanding here.
One pulls in the generator
One gives an 8s or 14s pulse.
Then the whole DC capacitor 3510 area.

There is an interlock to keep the clock correct signal from being generated without generator spinning. The is a hand key for the pulse and a switch for the generator. A rheostat to dial in the Hz...

So what's it doing or not doing?
After the xfmr unloaded in the old can there was no more automatic correct anywhere. We could connect the generator in hand and then key the clock correct and there seemed to be some appropriate movement on a test clock in the remote vault. One week has gone by and I went in there yesterday to key it by hand in the early morning try and get the clocks close to the right time. The job finally fell to me:grin: After I planned stay to watch it at 6am. The problem is that the key for the windings stopped working.

Too many open variables to troubleshoot yet:
  1. Gotta get a known good working clock ready as a tester. In the evening.
  2. Got to find the old frequency meter in the wooden box to be able to check for outputs. Looks like that thing has really gone missing.
  3. Got to be able to key the clock correct by hand and then see why the EMS is not reaching the same: is the clock correct relay picking at the mstr clock site? Need to be there at 0530 and keep a sharp eye for the 14s pulse.

My boss just wants me to figure it out from the schematic but I am not good at reading schematic.

Any insights would be appreciated.
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Senior Member
simpler version

simpler version

Can't edit my first post so here is more...

Basically my task is to map the triggers for each: the clock control relay and the generator start relay. The top two terminals [of the seven] are said to be local 110v power. The only relay that seems problem is the 3510. Going backwards from the 3510 relay it parrallels the key switch and then I have to locate the normal input which is supposed to be coming from the EMS.

Map it back and see if there is power at the intended source, starting with the local enclosure and then, moving to the other building, looking for the wires that are supposed to be leaving from the mstr clock. Of course they change colors in the generator enclosure are not the same colors that are leaving the mstr clock enclosure, with vaults in between [~500 feet].
Do these do anything other than tell time? If thats all they do why not just replace them with "atomic clocks" and call it good.


Senior Member
Do these do anything other than tell time? If thats all they do why not just replace them with "atomic clocks" and call it good.
I agree, after reviewing the pics there is far too much damage and missing parts to this system to ever have any hope of getting it going again.

Unless your customer has deep pockets and doesn't care about the cost, this is a losing battle and will ultimately end up making the OP look bad.


Senior Member
Do these do anything other than tell time? If thats all they do why not just replace them with "atomic clocks" and call it good.
We have had lots of failures with atomic clocks over the last five years.
Some timex especially clocks just stop working and park at 12, even if you bring them out into an open field. Can't even set by hand [with new bat of course]

The Elgins were a little better.
All atomic clocks seem to have issues in our buildings and we end up with standard battery clocks which is such a hassle at least twice a year.

Thanks tho!:)


Senior Member
I have to agree with the others, go new and it will cost less.

You have no idea how many bad components there may be.
It was working until recently and my boss thinks I should be able to figure it out.
I am usually pretty good at making things work.:roll:



Staff member
Good luck. If money is not an issue it is a fun project but it could get costly.


Simplex clock system

Simplex clock system

Nothing is not repairable.

Just the prestige factor comes in to play!

Like having a 1965 mustang or corvette.
Not a 1965 clock system.

Well be happy to discuss things with you AND HELP.
Was with simplex for over 13 years!


Just a start

Just a start

Tc = transmitter common / ie / one side of a 24vac transformer

td = transmitter power / ie / hot or other side of transformer
*don?t forget a fuse


tr1 = motor run input (starts motor min 10 seconds before you key
up any frequency

tr2 = ?a? frequency probably 3510 clock correction in your case

tr3 = ?b? frequency 6000 it looks like this would have been used to ring bells
* note it looks like an old 91-3 Master clock for coded bells with an aux programmer 655 or 675. These bells ring at the end of the cycle if arm is in the cup.

Your print indicates 24vac control relays if some one put 120 to them thy could be shot.

Does it work using the manual controls?


I still maintain a clock system like this in 5 school buildings. Simplex clocks are really reliable if you keep up with the maintenance on the equipment. It is considered obsolete, but I don't any of today's clock systems are anywhere near the quality of the Simplex clocks.


EC, Westchester, New York NEC: 2014
Well be happy to discuss things with you AND HELP.
Was with simplex for over 13 years!

That's probably a big help but are you going to be able to get parts that cannot be replaced with anything but Simplex? Simplex will only provide parts and service through their dealers. I have to ask, (and I'm sure I know the answer) why haven't you contacted Simplex to service this system?