Shruti LED6 doesn't lid


I finished soldering tonight and everything seems fine one the test, except LED6. I’ve redone all the soldering of the LED, the resistor, the IC, the resistorpack and the MCU. No good.

I doubt if this would be the problem, but is this the point that I should desolder the LED and see if i’ve switched polarity?

Thanks! Jasper

Oh, all switches work fine, including SW4!

I managed to loosen the LED. I measure 1V when pressing the switch and fall-back to 0 when I press i.e. SW3.

Can I conclude the LED is faulty (or has given up on me?)

Forget the last post

I measured the input of the resistors. All of the resistor LED get 4,5 V input, the resistor of LED6 gets a fluctuating input of 2.0-2.7 V. The output isn’t steady as well.

This is with the LED 6 desoldered BTW!

Thanks a million

I measured the fluctuating voltage on the corresponding on at ic 165 as well. Is the icfaulty? The other leds are fully

I am one step further. With some more measuring I found out the led six does light, but the voltage freaks out when led 7 is also lid. The opposite pin to led six on the 595 ic receives 4.45v, I found out after removing the ic. Don’t know the number, but it’s the fourth from the ‘bottom’.

There my quest ends, can’t find out where this voltage comes from.


I’d try another chip. Is that from a kit or a self-sourced build?

It comes from the kit. Is the slightly lower incoming voltage normal?

> Is the slightly lower incoming voltage normal?


Send me a private message with your address and I’ll send you a new chip.

Done this afternoon, thanks! Did some more measuring. The strange thing is the input and outputof resistor is almost equal now - can’t remember that from this morning - but the resistor still measures 220 ohm. Resoldered the led but it seems dead now. Can’t get my head around it…

After a short holiday, I’m back at it. Thanks a lot for the new chip!

Unfortunately, it wasn’t the culprit. :frowning: The voltage on pin4 of the IC still is 4.98V when only LED6 is to be lit, and in combination with LED7, the voltage is unstable between 2 en 2.7V (constantly moving). NB: that is with the LED6 unsoldered (which is probably dead BTW)!

I took a look at the solder points, everything seems fine. I resoldered everything some time ago.

I just connected the Shruthi to a keyboard and it seems to work fine. Great sound, no strange behavior. I have to hold my self back not to start soldering the display.:slight_smile:

Do you have any clue what might be wrong, based on the info above?

Thanks very much


You can measure the resistance between pin 5 (goes to LED6) and pin 6 (goes to LED7) of the socket of the 74HC595 (take the 74HC595 out) and also leave out LED6.
Maybe there is a short.

Thanks for the suggestion! Did that just now and nothing abnormal, no short between those pins at all.

Tried something else too, leaving out pin 5 of the 595 by bending is slightly. The unconnected pin shows these strange values (4.98 when LED6 should light alone, variable voltage when LED7 is switched on too).

Very strange! I suspect the 595 is controlled by the other IC, following the lines. Could that IC be bad?

Thanks again!

Are you shure you are measuring on the right pins?
Here is a picture which shows how to count the pin numbers on an IC.

Thanks! Redid the check and really no short or resistance lower than 1 on those 2 pins. I’m absolutely sure I got the right pins, even more after looking up the pin layout of the 595 IC.

Thanks again, Jasper

If the other LEDs light up correctly, the communication with the MCU is OK. I would look for shorts between the 595 output pin for LED8 and adjacent pins.

Strange. I’m out of ideas. The other LEDs are working and you have already changed the 595. All switches operate like they should. So the 165 IC is working.
I would suggest to just solder in a new LED6 and look how it works. (If there are no other shorts on the 595).

No shorts there, I’m afraid.

I checked the complete socket (empty, LED6 not connected). I came up with this:

8-9=1,466 kOhm

The other LED light up correctly, the Shruti makes great noises…:slight_smile:

The strange thing is that when (only) LED6&7 should be lit together, LED7 gets a perfect voltage, the LED6 doesn’t.

I’ll get a new LED tomorrow morning. Should I get a new 165 IC extra or does that make no sense?

thanks a million for your help

Time for a little update. Just soldered a new led. Lights great when only led6 is to be lit. In combination led6 flashes. So we’re getting a step further but I would love to eliminate the problem and finish the shruthi.

Any ideas what to do next?