Comments on: EXACHRON DCF77 Time Pulse Receiver Repair

By: Albert van Bemmelen

Albert van Bemmelen — Mon, 23 Oct 2017 20:31:34 +0000

In reply to Albert.

Thanks for your terrific contribution to find out how to calibrate the Exachron Taco! You are a real pro and I was astonished that you took the time to almost build the entire Exachron circuit on a big experimenter's board (or maybe two?) and managed to calibrate it with the four mentioned 10K 74123 potentiometers. And your tip to use a High Precision 25MHz MHS-5200a 12-bit 200Ms dds signal generator frequency counter timer (with Arbitrary Waveform function) definitely will make a big difference and is THE solution to adjust the correct length (in milliSeconds) of the time pulses! Thanks to the integrated precision Timer Counter in the MHS-2500A (Be aware that there exist an older model and an upgraded newer real 12-bit version). It probably is the easiest way to do, because it is something that was very difficult to check and adjust on my scopes. If my Pro watchmaker friend brings his old device a second time I hope to be able to make a decent calibration procedure manual for it, and maybe a third Final Exachron article that will be of great help to other Exachron owners too. It is not often that we find someone who went into such great length to contribute to a difficult problem. Again thanks Taco. I'll let you know how it goes if I know more!

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By: Albert

Albert — Thu, 12 Oct 2017 07:25:55 +0000

Hi Taco. I'm impressed that you were able to build the entire reciever from my Tina schematic. Although the DCF reciever of my friend did occasionally work as expected it most of the time didn't. So the repair was not entirely successful, mainly because I couldn't find any defect components on both decoder and display boards.
Therefore it still could be because of deviations on the reciever board with the 77.5 KHz Quartz on it. Or just the calibration thing with the 4 potentiometers on the right decoder board. And because no calibration procedures exist after all those years it is very hard to find the cause. After I had replaced and checked all defect TTL chips and had made all photos and finally the schematic I gave all back to my pro watchmaker friend Charles.
Anyhow I am almost sure that the diodes are just simple (silicium) diodes and not zeners and I will have to look back into my notes if there are any photos or notes of the project left to answer your capacitor, resistor question. I will try to answer them lateron. Maybe this even helps to find out what exactly might still be wrong with my friend's device.

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By: taco roos

taco roos — Sat, 30 Sep 2017 17:27:02 +0000

beste, ik heb de hele ontvanger na gebouwd aan de hand van de tina schema's en de foto's heb nu alleen een probleem kan niet goed zien wat de kleur codes zijn van de 8 weerstanden bij de 74123 ic en de 2 gele condensator cq dioden ook bij de 74123 zou u mij die kunnen door geven heb de ontvanger opgang werkt naar behoren maar net niet geod genoeg als ik de weerstanden goed heb en de 2 dioden of condensator de gele die tussen de 22uf en 100uf in ziten dan kan ik verder bvd
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Dear, I've built the whole receiver based on the tina schemas and the pictures have just a problem, but I can not easily see what the color codes are for the 8 resistors at the 74123c and the 2 yellow capacitors or diodes also the 74123 would you be able to give me those who are able to pass through the receiver upwards properly but just not geod enough if I have the resistors good and the 2 diode or capacitor the yellow that between the 22uf and 100uf in seats then I can continue to bvd

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By: Albert van Bemmelen

Albert van Bemmelen — Mon, 08 May 2017 08:33:02 +0000

And I recently also tested the Antenna Amplifier circuit as was given in the article. I had quickly build on a experimenter's board to be able to tell if it helped by further fixing/adjusting the reciever board. It worked great on the 15V from the reciever antenna input cable. However made no difference by tests in combination with the also special DCF Time pulse tranmitter I had build.
So both mentioned antenna amplifier, and the DCF time pulse transmitter worked great! The only chips on the Exachron I still had not tested or replaced were the 6 pins TBA861A and 8 pins 1458. Also because the reciever's board output was a correct DCF 200mS/100mS timepulse.

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By: Albert van Bemmelen

Albert van Bemmelen — Mon, 08 May 2017 08:05:57 +0000

I found a missing connection from /CLR_74164s to both U16_7400 1Y and U17_7404 2A. Now corrected in new send circuit!

And I also managed to make a working subcircuit of the Exachron timepulse reciever in Tina to examine and the 4 retriggerable monopuls flipflops in both 74123 ICs.
Because adjusting 4 analogue 10k potentiometers correctly without information is close to impossible! And after replacing all bad components I managed to get the Exachron synchronizing with date, time and seconds correctly running, but sadly it still was frequently wrong after switching on. So it must be a calibrating thing with the analogue 10k potmeters. And there are 7 of them on reciever and decoder boards. (plus one on the little sound board, but that one works ok). Although I checked the monopuls flipflop outputs on my oscilloscopes, it still was very difficult to know how to correctly adjust them. Also because of the very low frequencies of around 1Hz.

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By: Albert van Bemmelen

Albert van Bemmelen — Mon, 13 Mar 2017 08:33:40 +0000

In reply to Robert Calk.

Thanks Robert!
PS: if you look at the in Tina 10 made circuit attached to this article there is a small but significant error around transistor BC237B. The emitter needs to be connected too, and the ground symbol shorts one of the wires unintensional.
I corrected the circuit lateron but it was already published. Therefore if anyone needs it to repair his Exachron device he can ask me or Jestine for the corrected schematic.

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By: Robert Calk

Robert Calk — Fri, 03 Mar 2017 22:55:24 +0000

Good job, Albert.

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By: Albert van Bemmelen

Albert van Bemmelen — Wed, 01 Mar 2017 08:03:36 +0000

Addendum: After examining the circuit of the Exachron Time pulse reciever and creating it (reverse technology) in Tina design suite 11, I noticed that the 7447 and 7448 7-segment-decoder/drivers have a LT pin 3 function.

By connecting pin 3 to gnd (low level activated), all segments (being an 8) will light up as test function for the displays.
It showed that probably of the too high 5V supply some of the 7-segment leds already failed giving any light.
The simulation in Tina however runs even on my quad core PC too slow (factor 100 to 1000 slower than in real-time) compared to the Device. Which runs on 77.5 KHz. Also because there are 4 retriggable monovibrators used in the circuit with several capacitors that all limit simulation speed.

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By: Albert van Bemmelen

Albert van Bemmelen — Thu, 23 Feb 2017 08:38:32 +0000

PS: my smartphone editor is not that smart and it keeps interfering by changing my original intended text. Although I had switched it off!
See above Post where "Programmeren" was originally typed in as Programmer!

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By: Albert van Bemmelen

Albert van Bemmelen — Wed, 22 Feb 2017 23:02:08 +0000

Just finished building and adjusting the mentioned Elektor DCF transmitter tester. Works great up to a distance of about 10 meters! And I used my TL866A to program the ATtiny 48 with. Although the programmeren programs perfectly AVR and other chips, it is not compatible with BascomAVR in which the AVR was written. But if we adjust its configuration 'fuses' it will work just fine!

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