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IBM Need help trouble shooting a 2 wire IBM / Simplex system.


Registered User
Jul 12, 2007
Hi. I have a strange one here. I am hopping someone can help me figure this out.

Problem. 2 wire IBM / Simplex system runs one min faster then the master.
The particulars.
Slave clocks
are a variety of IBM and Simplex from 1920 to about 2000 most are IBM two coil high quality brass movement or Simplex one coil metal gears and 60 tooth wheel. There are no one min cams. (I think)
Boosters There are two boosters, one connected directly to the master, and one down stream in another wing. Both boosters are Latham PS8-24B
Master National Time and Signal MC-100
This is where it gets interesting. The master has a programing error. It's 2 wire output called Cincinnati D3 is as follows
XX:00 - XX:49 2 sec Positive pulse each minute (59 sec and 60th sec.) I know, That is wrong.
XX:50 - XX:58 2 sec Negative pulse each minute.
XX:59 One 2 sec Positive pulse followed by twenty 2 sec negative pulses.

OK, That's odd, but it seems to me, that it should work as long as the slaves are working OK but every clock in the building runs one minute fast.

More details. A lone slave connected directly to the master for testing keeps correct time.

If the other slaves in the building are stopped for two minutes, they will catch up to the correct time at the 59th minute. 12 hrs later they were still on time (I think) 2 days later they were one min fast.

They will run weeks and never gain another minute.

I want to ask the manufacture to correct the software (Firm where) in there master but it would help if I could tell them why it doesn't work.

BTW This is for our church school. It is a working system but I maintain it for free. That and the fact that it is OLD are why I am asking for help on this forum.


Thank You

PS8-24 B.jpg


Registered User
Nov 1, 2006
I'm not familiar with this, but you say the error is Cincinnati D3, I think you might look in the master instructions and see if there is an option for a Simplex 2 wire. I know that the Simplex model 2350 and 6350 had a listing in the installation instructions for competitive equipment you had to set the dip switches on the CPU I believe. Maybe the switches are set wrong.


Registered User
Jul 12, 2007
Update. I installed a home made three wire to two wire converter so now I have the correct pulses (Gets rid of the wrong 59th min pulse) The system is now on time and works as it should.

I know the 59th min pulse was wrong polarity, but I don't know why it made the system one min fast.

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