So for some reason, my 74LS73 ICs burned out or malfunctioned while doing the switch part in this circuit. (Around the START/PAUSE)

I opted to use a 74LS76 IC with the Preset and Reset set to Vcc while I build the expression written on the picture. So far the down counter worked however the 5th bit (still used a spare 73 on the last one) never goes into low voltage or doesnt turn off. The Reset of that 73 is set to Vcc and the J/K inputs are set as shown above. Also, how do I build the switch that controls the START/PAUSE without making my 76 malfunction permanently? The last time I built it was

Clock Above Dip Switch

Wire Below the Dip switch connected to the AND gate and the output is connected to the main clock of the circuit.

Should a part of the dip switch be grounded or something?

Also, after I build the reset OR Gate with the expression, should I manipulate Preset on the 76 or do I leave as is?

 

I made a 76 version however the counter does not move in this version. It just stays to 24

http://i.imgur.com/m51WfDc.png

 

So for some reason, my 74LS73 ICs burned out or malfunctioned

So you've learned a valuable lesson : always read the datasheets of parts that you want to use. According to the datasheets for 74LS series ICs the absolute maximum supply voltage is 7V and the recommended value is 5V. Why are you using 9V?

 

An easier to read, IMO, schematic with irrelevant information omitted:

I'm just going to get this out of the way... While certainly not the worst I've seen, definitely near the bottom. Unnecessary wire jogs and crossings, so much inconsistency.

how do I build the switch that controls the START/PAUSE without making my 76 malfunction permanently?

When your switches are open, the inputs they're connected to float. What logic level to you get on a floating TTL input?

As pointed out, 9V exceeds the absolute maximum voltage rating for LS TTL and is sufficient to have destroyed or made your ICs unreliable. They should be discarded so they don't cause difficult to troubleshoot problems later.

 

I

So you've learned a valuable lesson : always read the datasheets of parts that you want to use. According to the datasheets for 74LS series ICs the absolute maximum supply voltage is 7V and the recommended value is 5V. Why are you using 9V?

It's 5V in the actual. Forgot to change the diagram

Also to clarify, I did read the sheets and were working properly prior to connecting the reset expression

 

working properly prior to connecting the reset expression

There is no reason why connecting 5V to reset would damage components; unless something is not wired correctly.

If you want help troubleshooting your circuit, you should start with what you expect it to do and what it's actually doing.