Maker Pro
Maker Pro

Red seven segment led display

jerrywf

Oct 21, 2014
2
Joined
Oct 21, 2014
Messages
2
Hi all, I have a led display with one segment out , lower right side, Can some one direct myself as to where to start looking? It happens to be a Yaesu FT227RB. Thank you for any help from jerrywf
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
8,393
Joined
Nov 28, 2011
Messages
8,393
Hi there and welcome to Electronics Point :)

Yes, myself can direct yourself to two good sources of electronic components: Digi-Key (http://www.digikey.com) and Mouser (http://www.mouser.com). They have the largest range of components. They are both based in the U.S. and their overseas shipping rates can be high. If you tell us your location (better yet, put it in your profile - there's a place for it), we may be able to suggest some local suppliers.

The original displays for that unit is are Toshiba TLR312 common cathode units, but they're no longer available. A suitable equivalent probably exists, and I will dig it up for you if it turns out that the display is actually faulty. But I think it's more likely that there's a problem elsewhere - a broken track, a broken resistor, or possibly a faulty driver IC (the one marked MSM561 located beside that display).

Each TLR312 has five pins along the left edge, and five along the right. Here are the segments and pin connections:

TLR312 segments and pinout.png
You can zoom in on the picture by clicking it.

From your description, it sounds like segment C is out. That corresponds to pin 6, which is the bottom right pin, closest to the decimal point. That's the pin you need to check carefully. Follow the track through the resistor to the MSM561 driver IC and check for visible damage. If you have a multimeter with a continuity test function, use that to check the tracks. Flex the board gently as you test; it may be a very thin crack. If you don't find anything, let me know and I'll advise you further.
 

jerrywf

Oct 21, 2014
2
Joined
Oct 21, 2014
Messages
2
Kris, Thank you for the help Just want to forward a few details about myself. Been a ham since age 13 , I mostly have played with A M phone and run a few E.F Johnson rigs also Swan , National, Swan 250C, 101EE and a tton more including a BC610E. I have a number of solid state rigs (I like the older junk) but I don't know a lot about what I call the newer rigs. I thank you for your help you are dead on target, When I compare your info with the Yaesu work shop service manual it becomes clear (the manual is a little vague) I have checked into some forums with what I thought was a question of importance to me , And just got wise cracks and smart remarks. But then I thought These guys don't know any more then myself and I bet they could not tune up my Valliant or the BC-610 So for your help and kindness I Thank you many times. I have not been able to get back to the FT227RB today but will tomorrow. One more question about the driver on segment C, Does the driver supply voltage to the segment or does it close the seg. to ground. Will report back soon as I run the checks Thank you from jerrywf
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
8,393
Joined
Nov 28, 2011
Messages
8,393
You're welcome :)

The driver supplies positive voltage to the segments. The display is a common cathode type, and the common cathode terminal is connected to the 0V rail. So to turn segment C ON, the MSM561 driver drives pin 13 high (probably to +5V from the +5V rail). This causes current to flow through R622, into pin 6 of the display, into the anode of segment C, through segment C, and out the common pin to the 0V rail.
 
Top