It should read 20:28

Look for a bad connection on that segment - g.

 

Look for a bad connection on that segment - g.

How would I begin to do that?

Guessing..
1. with a meter
2. where/how?

As always, thanks folks.

 

It will be obvious only after 8 pm, and not at all in 12-hour mode.

ak

 

Look at the joint on pin 10 of the affected digit.

 

Start by looking at the solder connections along the trace that goes to the bad segment. Be sure that the solder is shiny and have flowed to a smooth connection.

It is even possible that you completely missed soldering one of the pins. The first computer I had was built from a kit. The memory boards had 8 kilobytes per board. That was 64 memory IC's with 16 pins per IC.

When I plugged in one of the boards it did not work. The assembly instructions recommended that the first step was to look for an unsoldered pin on one of the corner pins of the IC's. Lo and behold that is exactly what I found.

 

It will be obvious only after 8 pm, and not at all in 12-hour mode.
ak

this might become my fallback position, if I can't resolve it.

Look at the joint on pin 10 of the affected digit.

I am confused as to which pin is which.
I presume there is a standard numbering system for these tubes.
If I look at one of these (from the front), does the numbering go?
1 2 3 4 5
10 9 8 7 6

Start by looking at the solder connections along the trace that goes to the bad segment. Be sure that the solder is shiny and have flowed to a smooth connection.

that is easier said than done, Richard.


A lot of the soldering is obviously hidden behind the number display .

Are there any checks I can do, possibly using a meter, to discover why that middle segment is not lighting?

Thanks for all the help so far folks, it's really appreciated here.

 

This is a multiplexed display system, so no segment has straight DC on it. Measuring a segment with a DC meter should show some percentage of the system power voltage. Measure a few to get a sense of the range of normal values (probably less than 1.25 V), then measure the bad segment.

ak

 

I presume there is a standard numbering system for these tubes.

There is no single standard pinout for these displays. You can try Googling for "7 segment display pinout". There seem to be a half dozen different pinouts...

Another option is to use the diode check on a DMM. Put the positive lead on one of the common anodes on a display that's working and the other pins one at a time until the g segment lights. Then look at that pin on the display that isn't working.

You could also use your DMM to test the g segment on the display that isn't working. It's possible that it was damaged during soldering.

 

That is easier said than done, Richard.
A lot of the soldering is obviously hidden behind the number display .

Are there any checks I can do, possibly using a meter, to discover why that middle segment is not lighting?

I was hoping that the displays were in sockets. Since that is not the case things are going to be a bit more difficult.

You can continuity test from the bad segment to the same segment of each of the other displays. If you are not sure the pin for the bad segment you can do a reality check by doing the same continuity test between known good segments.

I see three possibilities at this point.
1. If the bad segment happens to be at the end of the trace it could be a cracked trace.
2. You have a bad solder joint for that bad segment.
3. The display has a bad segment.

It is very likely that you are going to have to remove the display -- either to replace it or to check the traces underneath it. This does not sound like much fun. The biggest damage is that you might damage the traces while removing the display.

 

You can continuity test from the bad segment to the same segment of each of the other displays.

I sort of understand what you're saying, but at my current level of expertise , I don't know how to put that into practice, i.e. I just don't know where to put meter leads?

If you are not sure the pin for the bad segment you can do a reality check by doing the same continuity test between known good segments.

again unfortunately, the above answer probably applies.

I was hoping that the displays were in sockets.

if I do it again they will be

Since that is not the case things are going to be a bit more difficult.

now where have I have that before, the story of my life...

 

Another option is to use the diode check on a DMM. Put the positive lead on one of the common anodes on a display that's working and the other pins one at a time until the g segment lights. Then look at that pin on the display that isn't working.

I don't unfortunately know which pin those what on my little setup.
Are pins 3 and 8, the common anodes? - Just a wild guess from looking at the schematic.
I think I can work out that pin G equals pin 10 (is that correct?) From the schematic

You could also use your DMM to test the g segment on the display that isn't working. It's possible that it was damaged during soldering.

if only I knew where to put the meter leads

 

Are pins 3 and 8, the common anodes?

Yes. You can confirm by using the ohm setting on your DMM to check continuity between the pins. If you have 5 pins on each side, 3 and 8 will be the center pins on each side.

It goes without saying that power needs to be off.

I think I can work out that pin G equals pin 10 (is that correct?) From the schematic

if only I knew where to put the meter leads

Put the positive lead on one of the anode pins and, with the meter on diode check, put the negative lead on the other pins one at a time until you've verified that all of the diodes are good. You should be able to see each segment turn on. As you're doing that, you can draw the pinout for the displays for future reference.

To reiterate, circuit power needs to be off whenever you're measuring resistance or performing a diode check.

 

In an attempt to try and find out the pin numbering, I found a number of the side of the display tube...
10016BTC

I tried googling it but all I got was bitcoin hits

 

Hello,

I have taken your fuzzy picture and taken one digit out of it.
I looked at all digits and composed the pin numbers at the display:



Bertus

 

3 and 8 are right and it tells you where pin #1 is. Try this http://www.chinaseniorsupplier.com/...70140/1_7_segment_LED_display_blue_color.html page for data.

 

Nothing...
Checked continuity with the power off as per your instructions
nothing...
Checked diodes with the power of as per your instructions

just to confirm it is 5 pins at the top, 5 pins at the bottom

Yes. You can confirm by using the ohm setting on your DMM to check continuity between the pins. If you have 5 pins on each side, 3 and 8 will be the center pins on each side.

It goes without saying that power needs to be off.
Put the positive lead on one of the anode pins and, with the meter on diode check, put the negative lead on the other pins one at a time until you've verified that all of the diodes are good. You should be able to see each segment turn on. As you're doing that, you can draw the pinout for the displays for future reference.

To reiterate, circuit power needs to be off whenever you're measuring resistance or performing a diode check.

 

Hello,

I have taken your fuzzy picture and taken one digit out of it.
I looked at all digits and composed the pin numbers at the display:

View attachment 123162

Bertus

Here is a data sheet for a similar part. Note where it shows pin 1. (It is across from the dicimal point).

 

Hello,

I have taken your fuzzy picture and taken one digit out of it.
I looked at all digits and composed the pin numbers at the display:

View attachment 123162

Bertus

Thank you bertus

 

KISS and Richard0

Thanks, I can now see the pin order.

10 9 8 7 6

1 2 3 4 5

..if I am correct.

But (see above ), I am not getting any readings even on the good ones, following dl324 instructions

 

Hello,

Can you check continuity between pin 10 of the faulty display and pin 10 of the others?

Bertus