Completed DIY kit but not working - Page 1
Forum section: electronics / beginners

author: dewcansam
author_rank: Newbie
timestamp: November 10, 2023, 02:41:25 am
content: I am very new to electronics after a career in programming. I thought one of the best ways to get better would be to do these simple DIY kits. I have done a couple with no issues. Decided to increase the difficulty and bought this one: Heart Shaped 4-Digit DIY Clock Kits <https://www.amazon.com/dp/B09Y53D5J1>I had no problem putting it together. I powered it up and ran into problems.1. The 4th digit does NOT light up at all.2. The middle bar (labeled G) does NOT light up on any number.I have tried to use the meter to see if I could find anything. I am totally in the dark and don't know where to begin. I am on disability and have less that 300 a month. So the only scope that I could afford is that cheap DSO knock-off. I can tell that it is not working correctly. It does seem to be somewhat ok.Can anyone give me any idea as to where to start troubleshooting ? Or what do I need to look for when probing with the meter ?This is the manual from the Amazon item pagehttps://m.media-amazon.com/images/I/B1643OMkt+L.pdfThat manual does not include the circuit diagram - so this is the updated manualhttp://attach01.oss-us-west-1.aliyuncs.com/IC/DIY-Manual/GY20350-Manual.pdfThere is a QR code in the second image on the store page. This is that link. I have tested them both and I have not seen anything nefarious.Thanks for any help, Chris

author: ataradov
author_rank: Super Contributor
timestamp: November 10, 2023, 02:52:59 am
content: When entire segments don't light up, the issue must be with a common anode. I would double and triple check your soldering, especially on all the parts related to that segment.You don't really need a scope for this, this should be possible to diagnose using a simple multimeter.

author: Martian Tech
author_rank: Regular Contributor
timestamp: November 10, 2023, 02:54:54 am
content: Sounds like S4 and G are not properly connected between the microcontroller and the display. My guess would be bad solder joints on pins 1 & 16 of U1, since it's a surface mount part.You could use an ohmmeter between U1 pin 1 and SMG pin 5 - you should see ~330 ohms. And measuring between U1 pin 16 and SMG pin 6 should show ~0 ohms.

author: dewcansam
author_rank: Newbie
timestamp: November 10, 2023, 05:45:34 am
content: Thank you. Yeah I did not even have cont from pin 1 to the other side of R7. So I reflowed U1 and it fixed both of those.However, for some reason I am still not able to get it working. Just displays "NSNS". whatever that means.I did go through setting the time and date and verified that all the digits display correctly. But once you set the time and leave the setting mode it goes right back to "NSNS".

author: ataradov
author_rank: Super Contributor
timestamp: November 10, 2023, 05:48:43 am
content: What exactly is "N" on the 7 segment display?

author: dewcansam
author_rank: Newbie
timestamp: November 10, 2023, 06:44:05 am
content: This is what it displays. All the time, except when setting the time or so.

author: ataradov
author_rank: Super Contributor
timestamp: November 10, 2023, 04:01:09 pm
content: This looks like may be some error indication. The MCU here reads a number of sensors, so it is possible that it is not getting the results it wants.The next thing I would check is the voltage on the GM and RM sensors. One of them is a light sensor another one is a temperature sensor, so you should be able to measure a voltage that varies with the amount of light and temperature, so just covering and heating the sensors with your finger should show some value difference.Another possible issue is the RTC chip. It is harder without a scope, but you can still try to measure the voltage on both pins of the crystal. It is good if the measured voltage somewhere between the GND and VCC. But if not, it is not a strong indicator, since measurement with a multimeter could have disrupted it.

author: donlisms
author_rank: Frequent Contributor
timestamp: November 10, 2023, 05:52:39 pm
content: Just as a general comment, if you're new to soldering, uhm... there's a good chance it's just the connections, rather than broken parts. Check each joint, as best you are able. Each point connected to the right point, and not connected to any wrong points. And then... all the parts turned the right way around. I other words, focus on the mechanical side. (And do not skip any checks just because they seem hard or tedious!)These will always be useful skills.

author: BrokenYugo
author_rank: Super Contributor
timestamp: November 10, 2023, 06:07:03 pm
content: Ideally check every solder joint with magnification or continuity test. I find these kits often aren't the easiest to solder and it takes perfect eyes with good light to see every defect naked eye.

author: ozcar
author_rank: Frequent Contributor
timestamp: November 10, 2023, 06:38:12 pm
content: Quote from: dewcansam on November 10, 2023, 06:44:05 amSo what does it display when setting the time? If it ever does display and allow you to set the time then the MCU must be able to talk to the RTC (DS1302).I'm with Alex in thinking it is trying to tell you something, but unfortunately they did not bother to document what it means. If not trouble talking to the RTC, my money would be on it getting an "out of range" reading for the thermistor ("RM").Edit:I just noticed that you already mentioned that you were able to set the time. So I'm even more suspicious of it having trouble reading the thermistor. Could be the LDR ("GM") but there what more does it need than a yes/no light/dark indication?They say that the thermistor is "10Kohm NTC". The resistance value for thermistors is usually given at 25°C, and the NTC, for Negative Temperature Coefficient, indicates that the resistance decreases with rising temperature. That is not a complete specification, as that alone does not allow you to work out what the resistance will be at some other temperature, say 20°C. Taking a bit of a guess based on the sort of thermistors commonly used, the resistance at 20°C might be around 12k, and around 8k at 30°C.In the circuit, the thermistor is part of a voltage divider together with R11 (10k), so by measuring the voltage across RM, and knowing the supply voltage (VCC), you can work out the resistance.https://www.seeedstudio.com/blog/2019/10/09/voltage-dividers-everything-you-need-to-know/#:~:text=Voltage%20Divider%20Formula%20%2F%20Equation,factor%20of%20scaled%20down%20voltage.Of course, that only works if the value of R11 is correct, and rule 1.5 of trouble shooting is "assume nothing" without checking.If you (carefully) removed the thermistor you could just measure the resistance with a meter. You could also replace it with 10k resistor and see if the nsns goes away.Similar story for the LDR, but less easy to guess what it might consider to be an "out of range" value.

author: floobydust
author_rank: Super Contributor
timestamp: November 10, 2023, 08:35:09 pm
content: TJ-56-513B Heart Shaped Rotating Led 4Bit Digital Electronic Clock DIY KitTJ-56-441A Little Bear 4Bit Digital Electronic Clock DIY Kit etc.Seems to be made byIC Station Shenzhen, could ask them.OR just go through the soldering and parts from scratch to find the mistake. Use a magnifier to inspect each joint.It has two sensors (CdS light sensor, thermistor) maybe one is reading way out to lunch. If the resistors are hard to see and confirm, use a multimeter.Otherwise there is only the RTC that might not be seen by the MCU. So check pin 1, the crystal and capacitors are correct.Note the two buttons are read using an A/D input as analogs.

author: dewcansam
author_rank: Newbie
timestamp: November 10, 2023, 09:59:48 pm
content: So I tested the photoresistor (GM) and the thermistor (RM). The photoresistor was working fine. The thermistor, I could not really tell, it stayed around 2v . So I moved to the Crystal Oscillator (Y1) and the DS1302 RTC (U2). I could not figure out what the meter was trying to tell me. Same with the thermistor voltage would stay around 2 with very little to no deviation.However, poking around with the meter across P4 (GND) and P2 (X1) and P3 (X2). All of a sudden it started working. Which leads me to think that it is the DS1302.I managed to get it working 2 more times. Then it quit working once again.Being very new and on disability, I wanted to hold onto the socket for other projects. No matter how hard I tried U2 was not coming out. OK OK I get the message. Always use the socket. Lesson learned.Since it most likely the DS1302 and that I can't get it out. What should I do ?I got reminded of a video I watched not long ago by ADB where he stacked a replacement on top of the bad IC. Is this something to consider ?What about just cutting it out the solder the replacement to the legs left behind ?Thank you for your help P.S. Thanks @floobydust I really hated posting links to the pdf but being on mint for some reason anytime I tried to copy from the pdf, it turned out black and could not be seen.

author: Manul
author_rank: Super Contributor
timestamp: November 10, 2023, 10:12:53 pm
content: Quote from: dewcansam on November 10, 2023, 09:59:48 pmNo, in fact it's unlikely that the DS1302 is faulty if it worked at least for a moment. Most likely crystal is just not resonating properly. I would resolder everything there: crystal, capacitors X1, X2 pins. If that does not help it's most likely faulty crystal (they might get damaged by mechanical or temperature shock). Or it could be incorrect loading capacitors.

author: ataradov
author_rank: Super Contributor
timestamp: November 10, 2023, 10:17:20 pm
content: Reflow all the solder joints around the crystal and capacitors.Also, take something metal and pointy, make sure it contacts your hand and touch with the other end each side of the crystal. See if that makes it work. This would induce 60 Hz signal and even if the crystal oscillator is not running, it may be enough for it to appear to work. This would be a good data point.

author: dewcansam
author_rank: Newbie
timestamp: November 10, 2023, 11:57:42 pm
content: Reflowed all leads involved 6 times, nothing worked.I was testing things with the meter again. Had it in continuity mode when it beeped when I was not expecting it to.It is testing continuity between P4 (gnd) and P5 (reset). Since the schematic shows P5 going to U1 P18. I did not think that it should be testing positive for continuity. i.e. P5 is going to GND as well ??

author: Manul
author_rank: Super Contributor
timestamp: November 11, 2023, 12:22:56 am
content: Quote from: dewcansam on November 10, 2023, 11:57:42 pm"Continuity" is normal. I suppose U1 is driving that line down (to GND) most of the time. I would try to replace crystal at this point. You might borrow a crystal from some clock you have or buy it.

author: ozcar
author_rank: Frequent Contributor
timestamp: November 11, 2023, 12:44:36 am
content: Are you still able to set the time? If so, and you go back to set again, is it just frozen at what you set it to before?Try cleaning any flux residue off the PCB around U2 and the crystal and capacitors.

author: ataradov
author_rank: Super Contributor
timestamp: November 11, 2023, 12:45:41 am
content: Also, post pictures of the soldering around that area. It is often easier to spot issues this way.

author: floobydust
author_rank: Super Contributor
timestamp: November 11, 2023, 02:14:11 am
content: I would double-check the crystal loading caps C1, C2 are correct at 5pF each and next to the 0.1uF (104) cap C3. Not mixed up.Also, sometimes a kit will include the wrong value parts. For C1, C2 could cause the crystal oscillator to not work properly or need a "nudge" to start up.

author: tooki
author_rank: Super Contributor
timestamp: November 11, 2023, 09:01:21 am
content: I’ve had more than one cheap Chinese clock kit where the crystal was bad. Also some where I suspect the loading caps were incorrectly selected for the crystal. I’d definitely focus the troubleshooting on these.

author: dewcansam
author_rank: Newbie
timestamp: November 11, 2023, 06:45:34 pm
content: My arthritis is acting up and I can't work on it right now. But yeah I will replace the crystal and caps once I can work on it again.Thanks for the help.

author: floobydust
author_rank: Super Contributor
timestamp: November 11, 2023, 06:53:06 pm
content: That looks good for soldering and the parts are in the right spot. The RTC kinda looks like a counterfeit.The DS1302 loading caps I see everything from nothing to two 27pF used out in the wild.No data on the chinese tuning fork crystals for their design load.Geekcreit EC1515B is the same circuit and using 10pF.You could even just have a bad design, I haven't done the math on the DS1302 xtal loading caps.

author: ataradov
author_rank: Super Contributor
timestamp: November 11, 2023, 07:00:38 pm
content: Yeah, the IC is almost certainly fake. I'd still expect it to function.I'd still do my experiment with touching individual pins of the crystal with a metal thing that you are holding in your hand.And then just replacing the crystal is probably the next best step. Try to keep the leads a bit longer so they don't bend as much at the base.

author: dewcansam
author_rank: Newbie
timestamp: November 11, 2023, 10:03:06 pm
content: Quote from: ataradov on November 11, 2023, 07:00:38 pmTried that, no change. Ordered replacement parts. So I will change out all of those components.

author: haygarth17
author_rank: Contributor
timestamp: July 28, 2024, 12:03:14 am
content: A site contributor (floobydust) pointed me to this post.I did a similar project with my grandsons and run into a similar display message (mine was CSCS, while all settings working but not saved) which means Clock Stopped. In my case I found the solution and your issue might have same root as mine.Check this link: /https://www.eevblog.com/forum/beginners/digital-clock-project-error/25/to see my post, conversation and solution I found.