BCD IC not working correctly

[Wessex]

hi

am using a MC14520B BCD IC, which according to its waveform diagram, counts up to 0-15 decimal.

I have built a test box, 555 timer generating 1hz clock , into BCD IC, then out to ADG406 multiplexer

test box is used to check 14 way multicore cable, each output from mux is connected to one end of cable, molex connector, then other end is connected to LED.

idea is , LEDS in box scroll on off individually, in squence, showing cable is connected correctly pin to pin.

what we observe at minute, is the MC14520B only seems to count to 8 ?

have i missed some connection out, does anyone have experience of using this IC ?View attachment mux schematic 5.8.12.pdf

 

[rfredel]

Hello Wessex,

this circuit is a good idea.

My first look to the schematic diagram shows no fault.

You write, the the counter only counts up to "8". That looks, that your counter or your MUX is dead.

Can you make the clock pulses for the couter by hand (step by step) and then control the outputs. Then you can see if the couter or the MUX has a fault.

I hope it will help.

Regards

Rainer

 

[Wessex]

Rainer

thanks,

i did think maybe there is hardware issue with counter, but, it counts fine up to 8 . then re-cycles ( 1 to 8 again and so on ).

unless i am missing something fundamental about the IC, way it works.

have had someone say to me about 24v to the mux, but again, if there was a supply voltage issue, then surely , it would over heat, and break down,
there is no physical sign of rise in temperature on either IC.

i am stumped, oscilloscope shows clock out of 555 timer is consistent. I will scope the output from the counter again tomorrow

 

[betwixt]

A3 appears not to be working but please check the power supplies to these devices. I haven't had chance to look at the data sheet so forgive me if I'm wrong, is it possible that the 12V logic level feeding the mux is insufficient to operate it's internal logic. I've seen these used on split supplies where a negative VSS is used but the logic inputs are referenced to the ground pin not the VSS pin.

Brian.

 

[FvM]

I'm missing any information about the waveform and voltage level observed at the A3 output.

According to ADG406 datasheet, the voltage levels are acceptable. I rather expect a wiring fault, a shorted pin, or at worst case a damaged chip.

 

[Wessex]

fvm

yes, think you could be right, either a duff IC, or, wrong connection, is on bread board, so will take a look tomorrow

 

[Wessex]

Rainer

and all others, thanks for help,

pins 7 and 8 on the counter IC had to be wired to 0v,

and on the mux IC, pins 13,27, 12.

all worked fine in end

cheers

 

[FvM]

pins 7 and 8 on the counter IC had to be wired to 0v,

and on the mux IC, pins 13,27, 12.

Pin13 is N.C., the others have been wired to 0 V - if we believe your schematic :smile: