Hello Everyone,

I am trying to fix a linear laboratory power supply using ICL 7017 IC along with a digital red led display.

THE ISSUE : the unit digit is not displaying after a short while the segment "c" corresponding to pin 10 of ICL 7017. This pin shows -3.14v hence stopping the display of that segment, whereas the other pins show a good segment display at +1.8v.

I changed the IC without success, and tried to turn on the particular segment directly and it works fine.

Any idea where to look at ? Thanks.

Hicham -

 

Welcome to AAC!
The first step is to post the brand and model of the power supply.
The next step is to locate a service manual and circuit schematic.

 

Welcome to AAC!
The first step is to post the brand and model of the power supply.
The next step is to locate a service manual and circuit schematic.

Hello,

Thanks, the model is ELC AL 941, but could not find it schematic.

Hicham -

 

Hello Everyone,

I am trying to fix a linear laboratory power supply using ICL 7017 IC along with a digital red led display.

THE ISSUE : the unit digit is not displaying after a short while the segment "c" corresponding to pin 10 of ICL 7017. This pin shows -3.14v hence stopping the display of that segment, whereas the other pins show a good segment display at +1.8v.

I changed the IC without success, and tried to turn on the particular segment directly and it works fine.

Any idea where to look at ? Thanks.

Hicham -

Try reflowing the solder to the pins of the display. I just repaired a frequency counter that had the same issue. Also, if there is a board for the display mounted at 90° to the main board, make sure the solder joints or connector joining the two boards are well connected.

 

Try reflowing the solder to the pins of the display. I just repaired a frequency counter that had the same issue. Also, if there is a board for the display mounted at 90° to the main board, make sure the solder joints or connector joining the two boards are well connected.

Thanks, will try it. Do you think solder issue might make the IC give negative voltage to that pin ? i tried to remove the pin of the IC from the socket; it works fine for 15 sec with positive voltage then turn to negative 3.4v, and then the display segment c goes off.

i will try resolder it and give some news.

Hicham -

 

Thanks, will try it. Do you think solder issue might make the IC give negative voltage to that pin ? i tried to remove the pin of the IC from the socket; it works fine for 15 sec with positive voltage then turn to negative 3.4v, and then the display segment c goes off.

i will try resolder it and give some news.

Hicham -

Heat can cause some flex along a cracked solder joint. So, yes, it may turn off after a few seconds. Also, negative voltage depends on the reference - is it common anode or common cathode? Is it low-side switched or high-side switched?

note: heat may come from anywhere on the board to cause warpage, not just the solder joint in question.