Dead display - new build


 
R

Reif Hammond

New member
Hi all,

I am new to Heatermeter but not new to electronics and soldering. I have a display problem - nothing is displayed. When I first apply power (12V to Heatermeter or 5V to the RPi micro USB) a few vertical lines appear on the display for a few seconds and then go away. I have both the schematic and the image showing expected voltages.

As I adjust the contrast pot I see the voltage vary from 0-5V (measured at both the near and far sides on the display board).

Otherwise, everything that I have checked seems to work. From the web interface configuration page I can:
  • See reasonably correct temperatures of probes 1,2, and 3 (have not hooked thermocouple to probe 0 yet)
  • Adjust the backlight from 0 to 100%
  • Turn LED 1, 2 and 3 individually on and off. Since LED 2 and 3 are controlled by the shift register this tells me that the shift register is talking to the ATMega and at least working on pins 1 and 15.

Playing with the push button (blindly) LEDs will go on and off.

Checking the voltages on the display connectors all appear ok, although hard to tell if bouncing with my voltmeter (any suggestions for a decent cheap USB based scope?)

I have checked continuity between the shift register output pins 2-7 and the far-side solder pads on the display board verifying my soldering - all are good. No shorts between the data pins either.
 
Since you've tested the pot and it's working, something else is amiss. Post some high quality photos of the front and back of the board to let us see if anything is obvious at the component level.
 
I would reflow solder on the shift register just for good measure. Particularly pins 10, 11, 12 & 14 on the shift register and pins 6,17 & 19 on the ATMega. Wiggle the legs a bit with the soldering iron to make sure solder flows to the other side of the board. I don't have a board in front of me to check, but do this on any traces in the ATMega/Shift Register/Display circuit that have traces on the other side of the board. I've found that sometimes solder doesn't flow through and make the circuit on the other side on occasion, particularly on boards that have sat on the shelf a while.
Other than that, a more menacing problem would be if too much solder has flown between the HM board and the display board and shorted pins together. You might check adjacent pins on the display header for shorts with your multimeter.
As for the bouncing pins, you are right, that is really hard perhaps impossible to see with a multimeter. I've seen people get hung up on that and waste a lot of time and frustration only to realize they still can't see the bouncing after they've got things working....
 
Reflowed, reflashed, checked for shorts etc. No Joy.

Used a bunch of jumpers and connected another display to the far side holes on the HeaterMeter display. It works! Looks like I got a bad display. Gonna be fun to replace.

Thanks for the assistance.

Reif
 
Reif Hammond said:
Reflowed, reflashed, checked for shorts etc. No Joy.

Used a bunch of jumpers and connected another display to the far side holes on the HeaterMeter display. It works! Looks like I got a bad display. Gonna be fun to replace.

Thanks for the assistance.

Reif
Click to expand...

That's a royal bummer.

Removal tip: on the underside of the display, flood the pins with lots of solder, moving your iron back and forth until the solder on all pins is liquid and the display should start coming off.
 
A few seconds on each pin with my old 140 watt Weller gun let me pull it through with needle nose pliers. Once I had all the pins out the boards were still stuck together so gently pulling apart at one end I touched the pads starting at that end with the gun which softened the solder enough to separate, worked down to the other end within about 30 seconds. Did not have to add a solder lake. Took longer with my low wattage iron (that I normally use) and a solder sucker to clean out the holes for replacement pins.

New display and life is good. First cook yesterday.
 
You must log in or register to reply here.

 

Back
Top