4PM Issue / No LCD
  • I finished soldering up my 4PM, connected the filter board to the control board and fired it up without the LCD attached. According to the build/test instructions, I was able to toggle around with the buttons to verify that the LEDs were cycling properly. I then soldered on the LCD display and tried adjusting the trimpot, but was unable to get a display to show up. The buttons would not cycle at this point and the 4PM seemed to be locked up. I have attached a photo of it powered on with the LEDs that are lit up. The backlight of the LCD does appear to be on.

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  • Is the backlight of the LCD lit?

    What is the voltage on the middle pin of the contrast trimpot?

    If the backlight of the LCD is lit, you need to check the soldering of the trimpot – you should at least see a row of squares on the first line.

    Also, it looks like the unit locks up in firmware update mode. This is a common problem, and has been caused by accidentally shorting the control board by the metallic plate on the regulator on the filter board. It is likely that you’ll have to replace the 74hc165.

  • The backlight is lit. The voltage of the middle pin of the trimpot is 4.65.

  • Then try turning it the other way round. The usual range is 0.5 – 1V for the characters to show up.

  • After many clockwise twists and reading the voltage down to the 0.5-1v range i got the row of squares to show up on the first line. Do I need to order a new 74hc165 to get the 4PM to boot now?

  • What is the voltage at pin 11 of the 165?

  • It shouldn’t be below 2.5V. If it’s below 2.5V there’s a good chance the 165 has been damaged and you’ll have to replace it. Good luck with that.

  • I did indeed blow the 165. Just replaced it. Thank heavens for solder wick. It was a PITA getting the 165 out. Everything is working now. The sound is so huge. I am really blown away. Thanks for helping me Olivier. BTW, the LCD screen looks like it has yellow characters. I purchased a 4PM kit. Wasn’t it supposed to come with a white LCD?

  • Yes, it was supposed to be cold white! This is crazy – it can’t be an error on my side since the only yellow LCD modules I have had here was an OLED module I have put in an assembled unit almost 8 months ago ; and two pieces of greenish-yellow which I still have on my desk (samples from LCD manufacturer to try new colors).

    Can you send a photo of how the LCD looks like?

  • I have attached a picture of the LCD. I am color blind, but the color is definitely not cold white. :) Do you know if it would be safe to resolder on the cold white LCD? I don’t want to damage any pads in the process. Maybe you could send me the correct LCD?

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  • Dude don’t do it! Its awful desoldering those things (they should be socketed!).

    The yellow OLEDs are cool IMO. You have a unique 4PM!

  • IF you really want to desolder the LCD cut the pins with a Dremel and desolder them one by one. Its nearly impossible removing all Pins at the same time without incinerating the whole Atmosphere….

  • Good idea Frank! Yeah, even though I have premium Kester solder wick. I don’t know if it is a good idea to attempt it. I already have had to replace the 165 and that was a bitch. Also, I added the (kit) included LED eyes (are these blue or white?) that go into the acrylic panel. I used 2 10k ohm resistors from the BOM, soldered everything up, but the LEDs don’t light up. :(

  • It’s not an OLED (there’s a glow of the orange/yellow backlight LED on the right hand side), but looks fine.

    I swapped the control board on my 4PM for one with an OLED and yellow LEDs instead of white. Looks like yellow snow lol.

  • @xtrmnt
    crank up the resonance!

  • @fcd72
    turning up the resonance will activate the LEDs?

  • sometimes…..

  • @6581punk
    Snow the Huskies have . . . . . . .

  • Well it could be lemon juice lol.

  • I’d rather like to think of Mojito…. is this already a Derailment™ ???

  • Hmm. Okay I stand corrected. I thought the b/w 4PM display was an OLED. Nice looking LCD then.

  • What are the odds that I got the random LCD with my kit. Maybe I should get a special prize. :)

  • @xtrmnt
    you already have a special price, this will bid worth a fortune some day like the Blue Marituis

  • Well, couldn’t you solderwick the solder from the pins on the LCD side? IE removing the LCD, not the LCD+16pin header?
    This way the only thing that would run the risk of being damaged would be the LCD pads, not the shruthi-1 PCB . .
    Having successfully replaced a LCD once, the only thing i remember is that it’s a major PITA :/

  • I was thinking the same thing. Desoldering the LCD side does seem like a viable option.

  • If you aren’t bothered about the LCD then use the dremel cutting disk to cut slots into the pads on the outside edge of the LCD board. Once the solder had been wicked away you can pull it away from the pins easier?

    Brute force, but possibly easier?

  • Cut the pins BETWEEN the LCD and the PCB and desolder one by one. Heat, push/pull (to your like) out the Pin and THEN remove the Rest of the solder either with Wick or by pushing thru a needle from a Syringe (the solder won’t stick on the Stainless Steel Needle!). Never try to remove a MultiPin Item if you can make it a single Pin Problem just by sacrificing a 0,05€ Part!

  • I don’t think you can remove the LCD from the header while it’s attached to the Shruthi. Not without a suction/reworking rig.

    Best you can hope for is to carefully dremel between them, likely sacrifice the LCD, and hope you don’t gouge or screw up any traces on the Shruthi board from all the hell you’re going to put it through.

    In all likelihood, unless you’re really great at this or really lucky, you will lose a couple of pads on the control board and you’ll have to solder jumpers back to the ATMega. It’s not the end of the world, but it’s a helluva lot of shit to go through when you have a functioning display.

    Next time socket the LCD. I’m doing this from now on no matter what. It’s way cheaper than buying a desoldering station.

  • Happy Shruthi! Thanks for the replacement LCD Olivier!

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  • aww, I kinda liked the yellow LCD :P

  • My wife said the other LCD was orange. I’m color blind, so those colors just run together anyway. Anywho, building the 4pm was a great experience and a very challenging one at that. Somehow I managed to not destroy the orange LCD, but at this point, I have no idea if it works. Now I’m working on my Midipal and it has its own set of challenges. After trying various solder tips, I find the chisel tip to be excellent for just about all soldering working from SMD to thru-hole. Also, everything flows better with the flux pen when doing SMD stuff. I use Kester brand for everything. Kester makes some high quality soldering materials. I am about half way thru the Midipal project and hope everything fires up the first time. :)

  • How did you do with the MCU? Post a pic!

  • The MCU wasn’t too bad (I need glasses lol), I found that putting a small drop of solder on the chisel tip worked best and flux penning all of the pads before dragging the small solder drop on the leads. I will take some pics when I get off work.

    Oh! and Frank suggested that I dremel out the LCD or cut the pins between the LCD and the board. I actually found a really cool solder trick to remove components (potentially save them) and in this case the orange LCD. Basically I applied a large pool of solder to the top part of the LCD pads, and essentially bridging all of the pins into one large line of solder. By doing this, I was able to heat all of the pads at the same time and was able to lift the LCD off of the header without destroying it. I then used solder wick to wick up all of the solder on the orange LCD! :)

  • MCU pic

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  • Finished Midipal :) Booted up first time no issues!

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