Problem wit led display and keyboard section

[piet]

I have build the relay computer and it works only through the TTL serial connection connected to Teraterm. The relay computer itself works oke and execute the test program as expected when started through te TTL console. But the keyboard section and the led displays on the PCB do not work. Only1 display lights up a zero and the keys does nothing when pressed. Only a rattle if key 3 and E are pressed. I have already changed the 74HC4017 and checked all connection in this section but the keyboard and display section stays dead. So now I suspect that the PIC from this section is not programmed but I have no way to find out. I have no programmer to read or program the PIC. The PIC was delivered with the PCB board when ordered through Tindie some time ago. Anyone have the same problem or have a solution??

[Francis Bauer]

Piet,

It is possible there is an issue with the U24 PIC, but perhaps we can troubleshoot a little more to see what we can see.

You said:

Only a rattle if key 3 and E are pressed.

Please explain a bit more by what you mean...

If you have a voltmeter or DMM, verify that U23 pin 16 (and U24 pin 1) does have +5v on them.

If you don't have a voltmeter you can carefully connect a LED through a 1k resistor (or any resistor near that value) to the pin and the other side of the LED to ground.

Note: The flat side of the LED would go to ground. These LED connections are only temporary for checking purposes.

If the LED lights up brightly then you probably have +5v on U23 and U24, which hopefully it will show.

Do you have an oscilloscope to check and see if pin 14 on U23 (74HC4017) has a clock pulse stream on it? If there is a clock pulse that would mean that the U24 PIC IC is indeed running, since it would need to be running code to produce the clock pulse stream.

If you don't have an oscilloscope you could carefully connect a LED through a 1k resistor (or any resistor near that value) to U23 pin 14 and the other side of the LED to ground.

Note: The flat side of the LED would go to ground. These LED connections are only temporary for checking purposes.

You should see the LED light up. If it lights up dimly that means that there is a reasonably fast pulse stream on pin 14. If the LED lights up brightly, pin 14 is stuck HIGH. If the LED stays off then pin 14 is stuck LOW.

Let us know what you find... Good Luck, happy troubleshooting...

Note: Joe Allen will eventually read these postings and weigh in too...

P.S. Congratulations on getting your Single Board Relay Computer working on the Relay computer side of things, now we just need to get the other parts working...

[piet]

Thanks for your reply, much appreciated.

I have all the tools, multimeter and oscilloscoop in fact I design circuits and PCB's myself so I am not a novice. All power voltages are oke. The Clock of the PIC16F720 does not go so the problem is that PIC it seems to be stuck high. I think it is not programmed at all. I have a TL866 universal programmer but as always there is no PIC16F720 to choose from the list so I cannot check this or reprogram it. If Joe reads this can you get me another programmed PIC?

[Joe Allen]

Hi Piet,

Message me your address, I'll send you another programmed PIC16F720.

Joe

[Joe Allen]

I should say send the mail to jhallen@users.sourceforge.net
I thought there was a direct messaging form somewhere, but I can not find it. Also you coud go through eBay or Tindie.