Segment LED doesn't work

[Firefly]

Hi
A segment LED to my MKI doesn't work see beelow





Please HELP ME i need this in yellow square



nothing appear with this mode by my multimeter



I find something with all other black compound it's transistor but nothing with the yellow square and i know it's this transistor control the vertical segment off in first and second picture i find this to the forum dwf.cc see below the picture in blue thank you ledwatch for this good work




HELP MEEEEEE !!!!!!!!!!!!!!!!!!!

[rewolf]

Do I understand it correctly: you found out that the mentioned transistor does not work?
Is there a drive signal at its Base (check with a scope)?
If there IS a signal, replace the transistor.
If not, measure directly at the corresponding IC pin. If there is no signal there, the IC is defective - you'd have to replace it.

[Firefly]

Do I understand it correctly: you found out that the mentioned transistor does not work?
Is there a drive signal at its Base (check with a scope)?
If there IS a signal, replace the transistor.
If not, measure directly at the corresponding IC pin. If there is no signal there, the IC is defective - you'd have to replace it.

thank you for reply
i don't have a scope i tested all pin transistor with my multimeter in mode diode, i unsoldered this transistor (yellow square) and nothing appear 0 i tested other transistor on the circuit board and all work you can see picture 1 and 2.
so i can test something i unsoldered a other black transistor to the same CB and soldering it a place to the transistor (square yellow) but i can try this this evening because i'm at work

[rewolf]

I'd rather not unsolder a working transister (unless you did it before with success) - it could happen that you have TWO non-working segment lines then.

You can replace the "yellow" transistor with a new one.
There are modern SMD transistors that will probably fit (SC-70 or SOT323 package). Any small-signal PNP transistor will do, e.g. BC857 or BC858. Note that the E and B connections of the modern ones are reversed compared to the old ones, so you must solder them upside down.

But if you know someone with a scope, look at the signals on the transistor pins, this will show immediately what's wrong.

[clockace]

hi, i think before you go to all that work w/those tiny transistors, if you could resolder the one you took off and replace the qc. that is an easy job and it worked on my mkII that was lighting only one digit randomly. i have a more lengthy post to sully008 if you want to read more. it is 22:30 here and i am going to bed. regards, peter

[rewolf]

...and replace the qc...

I'm absolutely sure it's not the quartz crystal. Of you can see all 4 digits and only 1 segment is missing, then the multiplexer definitely words, so there must be a clock signal. It's eiter
- the segment transistor
- the signal for output for this transistor of the IC
- a broken PCB trace for this signal

[Firefly]

I'd rather not unsolder a working transister (unless you did it before with success) - it could happen that you have TWO non-working segment lines then.

You can replace the "yellow" transistor with a new one.
There are modern SMD transistors that will probably fit (SC-70 or SOT323 package). Any small-signal PNP transistor will do, e.g. BC857 or BC858. Note that the E and B connections of the modern ones are reversed compared to the old ones, so you must solder them upside down.

But if you know someone with a scope, look at the signals on the transistor pins, this will show immediately what's wrong.

Hi
How you know it can be remplaced by a BC857 or BC858?

[clockace]

hi, i will give way to others with more electronics expertise. i know zip about that. i have only been flying by the seat of my pants so far and have not run into any really serious electronic pc problems. if i did, i would have no idea what to do. hope others can give the guidance you need and get your watch up and running. regards, peter

[rewolf]

How you know it can be remplaced by a BC857 or BC858?

I see no reason why not, if the circuit above is correct. Polarity, voltage and current ratings fit, and other parameters are not relevant in this application.
However, I see no base current limiting resistor, I assume it is in the IC, quite improbable that it's integrated in the transistor. This is a small uncertainty.

You can try the following: short the C and E pads of the unsoldered transistor with a 100 Ohm resistor. The missing segment should light up on ALL digits (a bit dim, maybe). If they do, then you know the LEDs and PCB traces are ok and that is must be either the transistor or the ICs signal otput.