K8055 digital in 2 always on

Kits PC Related Projects
1

Hello,

My K8055 kit seems to work well in all ways but one.
digital input 2 is always on.
I suspect a short somewhere, or a defect IC.
it does not look like a short after IC2 to me because:

I have compared the voltages (and voltage changes) from IC2 pin2 to the other digital input pins on this IC, and it seems that pushing the di2 button gives the same change in voltage on pin2 as pushing any other button does on the relevant pins on IC2.

After reading some topics here I tried to swap IC2/IC4, but the results were the same, so I suspect that IC4 and IC2 work fine :frowning: all of the outputs of IC2 (pins 14-18) behave like they should.

When all digital inputs should be off, comparing voltages over in/out on IC2 and in on IC3 for di1 to di2:
The voltage over IC3 pin7 (0V) << IC3 pin6 when both should be the same (no input, voltage high). The outputs from IC2 for di1 and di2 (pins 18 and 17 respectively) are the same (high).

Can you help me, what went wrong?

2

You may use an ohmmeter and check the continuity between pin 17 of IC2 and pin 7 of IC3.

3

looks like there is no connection, ohmmeter says the same thing when you connect IC2 17 to nothing. (I should know better words to explain that)

4

This indicates that there is a break between these pins.
Maybe bad soldering on pin 7 of IC3.

5

Connection IC2 Pin 17 - R30 = IC2 pin18 - R28
it looks like there is a connection.

Soldering looks the same (good imho) on all pins

6

But no connection between R30 and IC3 pin 7 ?

7

that’s correct.

edit: looks like there is a connection between the IC3 socket (@ pin 7) and R30. so this means IC3 pin7 is not connected to the socket. I am removing the IC to check for a bent pin or something like that. (would be quite stupid)

8

It was in fact, caused by stupid. it is fixed now. :slight_smile: thanks
everything is working perfectly well now.