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Thread: Music - Sound Board not working - Can I test a CHIP?

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    Default Music - Sound Board not working - Can I test a CHIP?

    Hi all,
    Better grab a beer for this one...

    In endeavoring to allow the missus to get more into the joy of 'soldering' and actually putting something together and see the fruits of one's labour working - and she enjoys listening to music on her BT speaker whilst in the bathroom, I came across this cheapo spectrum LED thing...
    Just the ticket laddie!

    After hours of putting those LED's in and the - actually very few - components, 4 hours later, we waited with baited breath, and turned on...
    And I get the look...!

    So, basically, It's not working! LED's 'seem' to be flashing in a random manner.

    I assume that none should light up on start on, until some sound is picked up by the microphone, and the pot allows the sensitivity.
    I mean, holy crap! It's about 7 components (besides the LED's). What can be wrong...!??

    OK: NOTE - I bought two kits - just for a backup/spares.
    I have double/triple checked all the soldering.

    There is ONE weird thing. The STC base had a missing leg. I just put a post though the PCB and up through the IC base and soldered the STC IC leg to it.
    HOWEVER, the second kit, has all the base legs...!

    The LM358P (audio amplifier), chip gets hot!
    Is it possible for me - in a very basic way - to test using Ω's or some setting on my DMM to see if it's working ok?
    Both LM's got hot.

    As I bought the two kits at the same time [ONLY SOLDERED ONE UP!], I have swapped over the LM and STC IC's, and the same fault occurs...???
    Coincidence, bad batch...?
    So I checked all the soldering joints again. All look good.

    Pressing SW1 and rotating the POT seem to do nothing...

    I've contacted the seller, but alas, heard nothing back

    In the photo's there's a + and - pad near the USB PS. In both kits there's no component to go there.


    Photo's and hopefully a video (that might work), to show startup...

    1st: The Video: Fingers crossed..


    Humm, Maybe a Onedrive link....



    2nd Schematic:


    General PCB shots:









    As the LM chip is getting hot (as the backup chip), could it be a faulty batch of LM's? Is there a way for me to test the pins/legs..?
    I can't see how this LM can get hot. As the board was running, I was turning it around, looking and my finger got hot. Ow! So that's how I found it

    Anyway;
    If any of you experts can shed some light onto if I can check this LM IC, or what might be causing it to heat up, that would be great

    Cheers,
    GT250.
    Last edited by GT250; 12-05-24 at 05:13 PM.



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    Opps.

    Just some photo's of the raw PCB.




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    Search YouTube ... rudimentary example (not in English but you can see the DMM diode-check values) ...search for 'how to check lm358' or such.

    Again, black PCB (can't see traces) so no real idea what's going on (LM358 should not run hot tho') ...but you should know the drill now...ie; possible PCB error. bad LM358, instructions are wrong, or the STL upc has been programmed with dodgy code.

    edit: looking at added pictures....



    Orientation of silkscreen puts uPC pin 1 on 'inside' (closest to LEDs)

    However, the assembled PCB depicts upc pin1 at the 'outside' (away from LEDs)




    Unless there's a PCB silkscreening error, I'd hedge a bet that *both* ICs were meant to be soldered to other side of PCB. same goes for the LM358 (reverse connected it very much will run hot....or is possibly dead)

    You have to watch out for this crap with cheap chinese boards =)
    Last edited by wotnot; 12-05-24 at 05:48 PM.

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    Step 1 Pull both IC'S out of their sockets.
    Step 2 Power board up.
    Step 3 Measure the voltage at pin 8 of IC 2 (U2) Should be 5V.
    Step 4 Measure the voltage at pin 12 of IC 1 (U1) Should be 5V.

    If ok then check that is the way that they were plugged in.

    The more I look at it, the IC's are incorrectly orientated.
    Last edited by Reschs; 12-05-24 at 08:36 PM.

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    ...Yeah, ICs incorrectly mounted (and cap, mic, trimpot) to wrong side of PCB ....switch is soldered to correct side tho'.

    As for those 2 (power) solder-pads .... there to attach flying leads instead of USB port.


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    Hi Guys,
    OMG!!!! What a rookie mistake... !!!!

    Wotnot, yes another Black one, ha ha...
    Reschs's: I might end up doing that to see if I haven't done any damage to the IC's or other bits.

    I think it's - besides my overall dummy mistake - a case of seeing 'wood for trees..'

    We were so intent on having (or thinking), that everything should be on the 'face' of the PCB, except of course the PS socket...!


    I remember so many times talking her through the IC notch - of which when reading the manual (yes we both read it, LOL!) - it says "Put the U shaped notch direction of the IC base and the U shaped notch of the chip corresponds to the base..."

    Jeeze, I have to laugh, OMG!!!!...

    It'll be an afternoon of de soldering...
    I'll post the results - if nothing goes haywire when I get back!

    Once again, this is why having another set of eyes is the best!

    All good fun
    Cheers,
    Alan.

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    We were so intent on having (or thinking), that everything should be on the 'face' of the PCB, except of course the PS socket...!
    Typically components are mounted on the same side as their silkscreen print identifier =)

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    Hi guys,,,
    Well, I don't know why I do this..
    First: it's not working.

    Changed over everything as I thought was to be done.
    Something very SPOOKY happened when we changed over the IC bases to the other side:

    A test post, to see if the video -with audio works. OK. Nope not that way..!
    Second test: Now note that she is not touching the IC, just hovering over it.

    The whole complete LCD panel 'flows' as the finger hovers over the LM IC [Video clip hopefully with Audio].
    NB: Without touching the LM chip and hovering over it causes the whole LCD panel to light, scrolling around as the finger moves over it...!!


    Next is softly stroking the LM IC, on its base.


    As you can tell below, it was hard to remove the old bases!!! However, I did have a second kit



    Please note: That I did swap over the spare second kit LM and STC chips (into the 'reverse' polarity), bases before. So I am not sure if I have damaged either of these IC's, as the first 'run' the LM chip got hot. After I replaced the spare LM it sort of didn't get as hot... Sorry, can't recall it to well...

    So after replacing the IC's, it still didn't work.
    Replaced the POT, just in case.
    Put the Microphone over to the other side, no good.

    Underside:


    Topside:


    Turning the POT about and whistling, shouting, makes no difference. The SW1 doesn't seem to do anything...

    Good news is, is that all the LEDs are working fine LOL!

    Anyway, all good fun. Such a shame that putting the IC's the right way around and - for the hell of it - putting the POT, to the correct place, didn't make any difference.

    Cheers,
    GT250.
    Last edited by GT250; 13-05-24 at 06:24 PM.

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    This...

    Please note: That I did swap over the spare second kit LM and STC chips (into the 'reverse' polarity), bases before. So I am not sure if I have damaged either of these IC's, as the first 'run' the LM chip got hot. After I replaced the spare LM it sort of didn't get as hot... Sorry, can't recall it to well...
    Both LM358 op-amps will be dead. That's not a problem, they're a dime a dozen part. ($3 at jaycar)

    If after replacing the LM358 the display doesn't work as expected, then likely it is both the STL uPC chips are damaged as well...but I doubt it, just now looking at the schematic and visualizing how the IC would've been connected...(and if it did get damaged, it'll show up in the LED display) ... but I don't think it would've damaged the analog input circuit of the IC (signal from the mic), so replace the op-amp with known good LM358 and retest.

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    Yeah, Wotnot,
    I was actually in JayCar yesterday picking up some low melt solder (so as to mix in with the 'normal' solder), to help suck up in the de-sodlering process...

    I'll pick up a LM358 later this afternoon..

    BTW, do those Video Links work for you guys out there?
    They work on my side, but not sure if you guys can See/hear them (my first try at linking a video).

    Oh, and what a strange thing that hovering ones finger over the LM358 activates the circuit. Bizarre! Wouldn't be heat could it? Or like that Theremin electromagnetic field effect?

    Cheers,
    GT250.

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    Yes, I didn't check them before, but the video links work... and now that I view them, seems the STL chip may be ok.

    The response from putting fingers near/on the LM358, is random noise induction (mains hum, other signals human body picks up).

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    You probably missed the fine print that said that the kit was actually for a Theramin. {I'll get back in my box now}
    I'm out of my mind, but feel free to leave a message...

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    Quote Originally Posted by lsemmens View Post
    You probably missed the fine print that said that the kit was actually for a Theramin. {I'll get back in my box now}
    Nah, that's a different kit.... =)

    These look pretty cool.... .....

    ...but if you want hardcore hands-on assembly.... with

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    Hi Guys,
    OK: I picked up a couple of LM358's a 'N', whereby the original was a 'P'. However, there appears to be no difference at ln the specs.
    Picked up a few 8pin bases and a 28pin base, as the ones I de-soldered didn't come out well, in case we put together the second 'backup' kit..

    Popped in the new LM and zip! Nada....
    But it's working, however, there must be a 'sensitivity' option - POT - somewhere...

    One has shout at the mic to get a response!

    OK: I moved the mic to the front.
    I tested the 50k pot and all was ok. At 50k it is at its most sensitive.
    I tested both mics - 1.1MΩ and 1.2MΩ.
    I replaced the 50k pot with a 100k pot and it did make a difference - alas, requiring a lower shouting...
    Should I put a 500K one in, or am I chasing my tail...?

    Back to the spooky touching:
    If I put my finger onto the leg of R20 (closest to the MIC), I get the LEDs to activate!

    So what could be causing the lack of sensitivity?
    Could a R be faulty? I don't mind snipping a few legs to test the Ω's out of circuit, but - as a dummy - it shouldn't matter about the polarity of the R's and which side of the PCB they are on..?

    The 470 cap should be ok, it's in the correct polarity - even though it's upside down. Or not - no way!!! Surely!!!??
    The 104's should be ok as well.

    So here's a few videos: Hopefully I can get it right. Has audio.



    100k Pot.





    As for that Thermin
    A long time ago, in a land far far away called Sydney, I bought that kit (probably the earlier version!), from Silicon Chip.
    I had the pleasure of talking to the designer of the board and he kindly allowed me to send it to him so he could fine tune it for me.

    The missus's has a niece, who - is difficult - but likes all things musical. I have contacted Jaycar and they have a 'Last One' in stock.
    I have ordered it. I think the missus's will enjoy (one hopes), putting together a full kit (box and all), to her niece.
    We gave the niece a finished LED rotating clock (that Wotnot knows about these things ) and she was overjoyed with it, going around to everybody saying "Look what BB has made me!!".
    Special moments...

    Anyway, all good.
    Cheers,
    GT250.

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    The mics are electret and polarity conscious, is it in the correct way ?
    Could have been damaged.

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    +1 on what Reschs points out...those inserts have a little pre-amp builtin, they typically don't survive reverse polarity excursions. (why I'd already drawn a purple circuit around it

    It sounds like the op-amp is floating... the mic insert might be stuffed, but they shouldn't carry on like this...I'd be checking if the ground path is good at the base of the R17/R20 divider (if it were missing, ie; PCB error...it'd account for the behavior) You have to double check circuit path in yellow/red boxes, but you probably have to start with a known good mic insert (because a shorted mic insert will behave similarly)...

    ...OTOH the ADC input pin on the STL-15 IC may be toast...(both of them 'coz they were both in circuit badly)...I didn't read thru the datasheet, but ADC inputs can be voltage limited, and die if exceeded ...I don't think this is the case though, as it responds to induced noise =)

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    Hi Guys,

    Reschs: With the mic, it looks as though the placement on the PCB (off set pins), can only go one way without interfering with the LM. I've swapped over the mic - and - and - I just checked that I had swapped the mic over afterall, once I had to put the LM on the otherside - and guess what...?

    There's remains of a pad on the POS mic post!!! OMG!!

    And WOtnot, guess which R the + of mic goes to... R20...!

    I just have enough time before I Shoot off to work, to take a phone shot off the screen (so low quality).
    Jaycar have them (mics), in stock anyway $3.80, if I need another, but I'm pretty sure the polarity's been fine...



    It's either these Black Boards that are shit (as Wotnot says), or I'm really bad at desoldering!

    When we were making the clock, used sometimes, a heated soldering desucker (mains powered), for speed etc. Then when I realised that the pads were coming off I though the suction was too strong.
    I then went back to my old Goot manual sucker - of which I have only used on this music board.

    Ok, have to go.. But will certainly sort that mic and - track - now when i get back today.
    Ohh, so close..!!!

    Cheers all.
    GT250.

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    And WOtnot, guess which R the + of mic goes to... R20...!
    Not going by the schematic, and if that's so there an error here.

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    Hi all,
    Yes Wotnot, you are correct. I was in a rush and these black PCB's are a PITA..!!

    MIC + pad I think it goes to R18 and then to C3 - on the other side to the pin/leg opposite 1 on the LM.
    I'll have to wait till this afternoon to follow the - pad properly, but it seems to go nowhere on the 'non soldering side'.

    I checked the tracks maybe three times. Spent half an hour. Couldn't find a break. Had a break, went back and the tracks look ok with Ω Beeps from the DMM.

    I extended the MIC legs so that I could test the pad/leg contacts in circuit. All seemed ok.
    I might do it with the 470cap and test that whilst it's out.

    Of course I am missing something, lol!

    After all the checking, it still does the same. Only response is tapping the top of the mic!

    I don't know.
    Thank you for everyone's help guys. I really do appreciate it.

    On another downer: The new Hot Air station arrived yesterday. Wrong Voltage and incorrect nozzles! I have double checked the order and all the emails with the order, show the 240v and the set of angles nozzles. Now a battle to send it back...!
    Can't win

    Cheers,
    GT250.

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    Hot air stations are a real PITA.. Good for certain repairs. Most of the time I end up using solder wick to remove solder. Keep up the good work GT, you'll get their mate.
    Last edited by Johnno; 16-05-24 at 10:05 AM.

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