Blank LCD & blinking LEDs

Just assembled my first Shruthi and reall enjoyed the experience! But… Followed the instructions to the letter, tested the unit before soldering the LCD, booted OK, LEDs 3 & 7 lit up fine. Soldered in the LCD and the screen remains blank although the backlight is on. Trimmer has no effect in either direction. And now LEDs 3 & 7 are flashing off and on. Any ideas anyone?

make sure nothing is shorting out to the Vregs on the filter board.

You may need to turn the trimmer 20+ full turns before you see anything on the LCD.

How many turns did you turn the trimmer?
Are you certain that the soldering on the ATMega & 165/595 chips is good?
Post a picture if in doubt :slight_smile:

Woah, you guys don’t hang about! Cheers for the swift reply. V regs DEFINITLEY not shifting anything, made sure about that when testing! Soldering on the chips is good, quadruple checked the ATMega before placing the LCD. It did seem to boot OK before the screen went in, just not after it went in. Didn’t try the trimmer that many turns, just the four or five as recommended. I’ll give it a proper twist when I get back to it. Not tonight though, unfortunately I’m working (to pay for an Ambika…!)

Sorry, autocorrect! Vregs aren’t shifting anything, they’re not shorting anything either…

Leds flashing - in a regular or random way?

Did you check the voltages now with the display in place too? If your PSU is a bit too weak this could happen (the display adds quite a bit to the total current used).

Bytefrenzy------LEDs 3 & 7 flashing on & off and button presses seem to yield random patterns but without the display I don’t know if this reflects normal behaviour or if something isn’t right! Larsen----PSU is outputting 9v @ 1.2 amps.

Pressing a button should generally make something happen just to the LED that is close to the button in question, it should not generate random light shows.

You PSU should be big enough then!
But the feeling I get is that there is either a short or a dodgy solder joint somewhere. A high-res picture of your control board could be helpful.

I’m thinking over-enthusiastic soldering could be the problem, Larsen! The lights were responding perfectly before the display was soldered, I’m hoping it’s as simple as a bad joint on the screens solder joints causing the odd behaviour.

Did you trim the leads low enough inside the white box where the LCD sits? Make sure nothing is shorting out there and also there aren’t any solder bridges on the LCD pins.

Yep, they’re as short as they’ll go without actually scraping the board. I’m thinking there’s a short on the board side of the header connecting the screen, either that or too much flux, not enough solder!

Maybe just go through and reflow all of the LCD points.

A bad solder joint would have next to no influence on the behaviour of the LEDs…

The LEDs only started playing up after the screen was put in place. An unlucky coincidence, maybe?

Probably not… Check for any possible shorts around the LCD connectors, a stray bit of wire for example. Also check that the LCD frame isn’t shorting out some of the MCU pins - usually the frame is non conductive but there are exceptions (don’t know if this was a kit). Also check if turning the encoder gives the same led blinking as the switches. Finally, for the contrast, I have always needed far more than those four or five turns. It always seems like forever turns. End to end is twentysomething turns but when you’re fiddling with a tiny screwdriver you’re probably counting half turns and not full turns.If in doubt measure the voltage between the middle pin and one of the outer pins and check if it varies with turning.

Yups. Only thing could be if you have bridgets the Power Line and GND, so check adjacent Pins for shorts.

Could be…
If a bad solder joint around the buttons or the HC165 shift register causes the MCU to read random key presses it could explain the random LED stuff - so don’t just look at the joints near the display. I’d inspect them all :slight_smile:

Okey dokey! I’ve just been able to nip to the house there and had a quick look at the control board, there’s a few dodgy looking joints alright! Especially around the quartz, looks to be held in with little more than flux on one of its pins and the LCD header… well, I’m not going to embarrass myself further by describing it…! I’ll get the iron heated up at the weekend and do it right this time. Darn the audio demos I’ve seen, I was a bit too eager to rattle some windows! Cheers for all the advice folks, the forums reputation is well deserved!

Howdy folks! Ok, some progress. Re-soldered all the dodgy joints and got the trimmer set right (a lot of turns, good excuse for a sore wrist…. Now the display shows only mu for a few seconds, then shows 'mutable v 0.? That’s not a typo, the qustion mark is what’s displayed. I did read somewhere else on this forum that someone else had the same problem but I can’t find the post)