Leds lighting

Discontinued products Shruthi
#1

Hi guys, I’m having some issues at step 11 on digital control board.

Ok so, it suggests that while testing it we should be able to see leds 3 and 7
light up, and stay that way, and while rotating the selector watching other
leds form patterns [??].

1. What I had at first was no response on positions 3 and 7 but, while pushing
buttons and rotating the selector, I got some response from all the others
except 3, 7 and 8.

2. After I swapped the power adaptor endpoint module to a larger one, I got signal
from position 7, but no responce from 3 and 8. Still the buttons respond lighting
up other leds and I can hear a few subtle sounds and lfo’s, specifically from
position 6. But, then again, only when I turn the mixer channel volume all the way up.

3. It’s not really clear if it’s necessary to add those 2 little jumper wires
on each side of the analogue ports [marked R1 and R2]. I’ve only soldered
them… maybe that wasn’t even necassary, or it doesn’t matter at all [?!?]; it’s not clear.

4. One last, extremely important, thing I noticed is that on the digital board, that guy has
installed the IC socket [labeled IC4] with the notch indicating rightwards, while it is printed
the other way around… The correct thing, if we are supposed to strictly
follow the board printed indications would be placing it the opposite way, as I did. I’m really
surprised by the fact no one ever commented on that.

5. Oh and yes, I certainly didn’t go wrong placing the infamous shift registers IC2 and IC3
[74hc165 and 74hc595] on their respective places.

Looking forward to read you guys Thanks

#2

Hmm, I hope 595 is to blame. Much cheaper than LT1054 But I’m not sure.

And yes, I checked the orientation of every LED; because,apart from the triangle thing, when I use the trigger
or push the buttons, each position corresponds by lighting up the respective LED.

Just boot test fails by starting with LEDs 7 & 8 and not 3 & 7…

Is there something that could interfere in such a manner? Apart from cold joints or stray blobs, which I’ve checked
for a million times already.

Thanks again for helping me out, I’m pretty lost at this point.

#3

3. you MUST solder the bridges or put a Pot in, or theres no connection to the audio jacks, hence no sound.

While you are at it check that theres a Jumper on the Pole Selector Pins…

4. The orientation of the Socket is meaningless unless you put the IC in the right way.

#4

1. 2. Must be that the LEDs are wired backwards ; or that some pads on the 74hc595 are badly soldered.

3. If you do not wire pots, solder bridges. If you wire pots, you do not need them (or else pots won’t do anything).

4. Not a big deal… What matters is the orientation of the IC itself, not the socket.

#5

ok I did some resoldering, but now while I’m testing, leds 7 and 8 are on by default not 3 and 7.
I noticed that IC1 (lt1054) on filter board gets really hot after a whilet, is it normal ?

#6

Have you checked for shorts between GND and the +5V / - 5V rails?

#7

the only short I can see but I guess it is printed that way is between sw and 1N4004 diode. Where should I be looking ?
Do you mean the regulators ?

#8

Use a meter in continuity testing mode and check if there is any short circuit between GND and points at +5V / -5V. Have you performed the voltage checks in the assembly instructions?

#9

I ran the continuity test and when I probe pin marked with + sign on 7905 as well as on pin marked with - on IC 7805, I get continuity sound…not good news is it ? or is
it irrelevant ? In case it is bad news, any thoughts on how to fix it, because I can spot any shorts with naked eye.

#10

sorry I meant I CAN’T spot, or cold joints whatsoever

#11

There shouldn’t be any short between the +5V rail and ground, and the -5V rail and ground. Does your meter just beep or does it show a resistance value on its screen?

#12

Yep, 003…!

#13

It does both, it beeps and it countdowns till it stabilizes on value 003.

#14

Then you have a short between GND and the supply rail(s) unfortunately. You have to look for solder blobs adjacent to both a +/- 5V pin and ground. Or for ICs inserted with the wrong orientation.

#15

I checked LT7905 and LT 7805 datasheets, I was mistaken about what I said above, I beeping sounds out of the ground pins which is normal.
I also probed again using continuity test, the values suggested on step 4 of the SMR4 board, everything is clear. No “illegal” beeping sounds. Can think of anything else going wrong such as malfunctioning part, maybe a specific IC could be held responsible for such behaviour ?

#16

hello, are you here ?
I will work on the shruti this afternoon. Can you please answer me because I’m lost, the shruti is almost finish and I can’t go any further without help.

#17

Could it be a broken LT1054 ?

#18

LT1054 is for providing a negative voltage from a positive one, mainly for filter boards than use an OP amp as they require positive and negative voltages. If there was a problem with power to the digital board then it wouldn’t function at all.

Are all the joints on the 595N chip okay? no shorts? sometimes you can’t see the short as it is very slight, especially on the black boards.

I suppose you could also measure the output at pins 2 and 6 of the 595N chip to see if it is outputting anything, if it isn’t then there’s a problem around there.

#19

Thank you for providing an answer! I was thinking the same about LT1054, but was annoyed by the fact that it raises some high temperatures
really fast.

Till now, I have checked every each one of the joints many times; I have even resoldered some suspicious ones. Always using a magnifier!

So, I checked pins 2 and 6 of the 595 shift register and I get an output, that means things are clear down there. But, I’m guessing it’s got
to be a “routing” problem 'cause, testing it at step 11 now, I’m getting LEDs 7 and 8 on by default and if I press button 3 or 5 then it switches
to 3 and 7…

#20

Well if all the joints are okay, the LEDs are 100% correctly orientated then the only thing left to blame would be the 595 chip itself.

Are you 100% sure the LEDs are correctly orientated? you can usually see a little triangle at the side of an LED and they should all point the same way. They’re diodes and will pass current one direction only. So you should get little resistance one way and high resistance the opposite direction. This should be fairly consistent with all the LEDs.