Trouble shooting-Progress

More
1 year 2 months ago #9934 by MikeS
Replied by MikeS on topic Trouble shooting.
For those trying to figure out whether there's short in the decoder - early K155ID1s were like 7441s, they decoded inputs of 0xA-0xF as outputs 0-5 instead of blanking like 74141s. But, apparently, the Russians never changed the number when they changed to follow suit. So, I think the only way you can tell is to test.

Please Log in or Create an account to join the conversation.

More
1 year 2 months ago #9941 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic Trouble shooting.
Thanks for the tip, Mike. I had forgotten all about the differences between 7441, 7441A, 74141, etc. when handling overrange input.

As it turns out, once I got the translation table sorted (more below) the "strange counting" we see in the video could be caused by the "C" bit of the BCD being held high all the time. "C" comes from Pin 14 on the ATMega. 14 is the last pin on the left side of the package, so it only has one neighbor, Pin 13, which is used as the button input. Provided the button is not being held down Pin 13 will be floating at +5V because of the weak pull-up in the controller.

I'll give it an 80% chance that you will find a solder bridge between Pins 13 & 14 on the ATMega. If there's no bridge there then look at Pin 7 of the K155. If either Pin 7 of the K155 or Pin 14 of the ATMega (these are the 2 ends of the "C" trace) are not connected the K155 input pin can float itself high and produce similar symptoms.

About those translation tables... it took me forever to snap to this :blush: but I finally realized the digit translation Ian posted upthread isn't right. The subscript is the digit you want displayed and the value of the referenced array element is what you send to the K155, not the other way around. Parsing that, we get this table:

digit you want -- what you have to put on the K155
"0" -- 0010
"1" -- 0011
"2" -- 0111
"3" -- 0110
"4" -- 0100
"5" -- 0101
"6" -- 0001
"7" -- 0000
"8" -- 1001
"9" -- 1000

This is what the clock in the video is doing:
"3" -- 0110
"2" -- 0111
"2" -- 0111
"3" -- 0110
"4" -- 0100
"5" -- 0101
"5" -- 0101
"4" -- 0100
and presumably
"blank" -- 1101
"blank" -- 1100

Compare the 2 sequences - the difference is that C bit is always on in the second one.

Look into it later when the dust is clearing off the crater.
The following user(s) said Thank You: Ian

Please Log in or Create an account to join the conversation.

More
1 year 2 months ago - 1 year 2 months ago #9953 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic Trouble shooting.
Actually, upon further reflection, I'm changing my bet to it being my second option above: either Atmega Pin 14 or K155 Pin 7 being disconnected / open circuit. Or maybe the trace that connects Pin 14 to Pin 5 is cut. If it was Atmega Pins 13 & 14 shorted together I think we would see other strange behavior because Pin 14 would, periodically during counting, pull Pin 13 (the button input) low.

Look into it later when the dust is clearing off the crater.
Last edit: 1 year 2 months ago by Ty_Eeberfest.

Please Log in or Create an account to join the conversation.

More
1 year 2 months ago #9954 by Ian
Replied by Ian on topic Trouble shooting.
Oh good call Ty!

I had a nagging doubt that my table might be wrong.

Please Log in or Create an account to join the conversation.

More
1 year 2 months ago #9956 by Ian
Replied by Ian on topic Trouble shooting.
OK, let's test some voltages: Check pin7 of the K155. It should go high and low, but I guess it is going to read 5V. Here is the section of the board with that line highlighted. If it is TTL, it will float high, so you might not be able to test the voltage properly, depends on how you are testing it.

Attachments:

Please Log in or Create an account to join the conversation.

More
1 year 2 months ago - 1 year 2 months ago #9966 by SamIam
Replied by SamIam on topic Trouble shooting.
Ty & Ian,

Thank you. I'm on a business trip, but I will look real close at that when I get back next week, and let you know how it goes.

Thank you again for all the help, I really appreciate this.
Last edit: 1 year 2 months ago by SamIam.

Please Log in or Create an account to join the conversation.

Moderators: AccutronTy_EeberfestIan
Time to create page: 0.204 seconds

Search

Tube Suppliers

Go to top
JSN Boot template designed by JoomlaShine.com