e-licktronic Forum

Being a newbie, this is hard for me to explain clearly, so please be patient.
I was getting no sound for these instruments: BD, SD, Toms, RM, HC and CB. After checking everything to do with my soldering, etc..

Traced it back to IC114/IC3 (CD4051/CD4049).
Turns out that pin 10 of IC3 was sending a digital: '1' (positive square?) to pin 6 of IC114 (inhibit pin). This was preventing that 4051 from sending out the accent signal for those instruments.
Traced that back to pin 20 of IC119 (MCU). That's sending a digital: '0' (inverted square?).
So the 4049 is inverting that into a digital: '1' and that was stopping the sounds.
If I lift pin 10 of IC3 out of the socket, the instruments work no problem, because the inhibit signal is not being sent to IC114.

Conversely, pin 21 of the MCU is sending digital: '1'. The 4049 is inverting that into a digital: '0' into pin 6 of IC111. So the instruments that get their accent signal from that 4051 always worked from the start: CY, OH, CH and Accent.

My question here is, why are pins 20 & 21 from the MCU sending different signals? Is that intentional? My current understanding says that conflicts the inhibit pins on the multiplexers and as a result, only one 4051 will ever work. Can someone please help me to understand what it is I may have done?

Replace IC3 (4049). Problem solved.
ESD? Floating pin? Latch-up? PEBCAK? I've learned some terms

Hello,

I am having the same issues that you had with the accents on my instruments. I've followed the exact same thinking as you as for the reasons for that concerning the IC114 and IC3. And yes i've oberved also that pin 20 and 21 are of the MCU are sending digital 1 and 0 respectively. But this digital 1 is a +5V signal if i'm not mistaking and when it arrives onto my 4049 which is supllied with 15V (i'm not sure of that right now) the output of the inverter remain a digital 1 at +15V for the two signals (the +5V is recongized as a digital 0, i'm guessing). Did you observe the same phenomenon? Now that it works how does your 4049 and 4051 work? Because i'm still confused about the particular behavior of these circuits.

I've tried changing all the IC (4051 and 4049) but it didn't solve the problem.

Thanks in advance if you can answer me

First make sure the MCP4822 TP1 is providing +13V.

Then, using this part of the schematic for the accent:



These two are from the MCU pins 20 & 21:
INH_MUX1
INH_MUX2

So, something is causing them to read incorrectly. I would start there and ensure the MCU socket is soldered well, no shorts.

The Accent voltage originates from MCP4822 / TL072 (IC118 & IC6), which is the line coming from the top of the picture into pin 3 of the two multiplexers. The multiplexers divert that voltage to the individual sounds. The 3 TL074s must be amplifying the signal to create the triggers. The 4049 handles the MCU signals. Pin 6 on the multiplexer is the inhibit pin, which stops it from sending signals out. So, the ICs involved are IC118, IC6, IC3, IC114, IC111, IC1, IC2 & IC110.

Do any of the sounds work? If yes, then you know which multiplexer/op-amp combination is good. In my case, the crash, hats and PC were working, so I knew it had to be related to IC114; which ultimately is wasn't, it was the 4049 feeding into it. I started my journey of discovery by physically squeezing IC1 and wondering how the hell that was making it work It took me some time before I structured my approach from a mad initial panic.

Maybe a bad batch of 4049s? I got a couple of 4049UBE from eBay and one of those worked first off, after doing loads of unnecessary stuff. If that doesn't do it, try replacing IC1, 2 & 110. Otherwise, you will need to trace all the paths above to see if there is a short which is pulling the MCU pins.

Don't blow your MCU like I did, it can happen real easy and that sent me down another path...

Wow. Thanks for your complete answer. And everything is solved now. The issue was with the connection between IC3 and the MCU, i might have damaged the copper lines coming from the MCU to the IC3 so that there were no connection for three signals. So i replaced them with some jumper wires hoping it will last but as it is digital signal i think there won't be any issues. Furthermore I had also issues with one of the 4049 that I replaced also. Everything works well now. I just have to finish the Master and it will be over.

Thanks a lot for your help

You're welcome. I'm glad it's all working now.
Good find on fixing the traces from the MCU to IC3. I burnt out a trace in the noise circuit, swapping out the trimmer to get 130mV. It's easy done.

blotvard wrote: Maybe a bad batch of 4049s? I got a couple of 4049UBE from eBay and one of those worked first off, after doing loads of unnecessary stuff. If that doesn't do it, try replacing IC1, 2 & 110. Otherwise, you will need to trace all the paths above to see if there is a short which is pulling the MCU pins.

I have the same issue! May I ask which 4069UBE you bought from eBay? I have two from Texas Instruments (Tayda) that don't work.

KlangGenerator wrote:

blotvard wrote: Maybe a bad batch of 4049s? I got a couple of 4049UBE from eBay and one of those worked first off, after doing loads of unnecessary stuff. If that doesn't do it, try replacing IC1, 2 & 110. Otherwise, you will need to trace all the paths above to see if there is a short which is pulling the MCU pins.

I have the same issue! May I ask which 4069UBE you bought from eBay? I have two from Texas Instruments (Tayda) that don't work.

I had the same issue with ones from Tayda not working in my Yocto. I swapped them out for some new TI CD4049UBE’s from Digi-Key and those worked fine. I think there is an issue with the batch that came from Tayda.

secrethero303 wrote:

KlangGenerator wrote:

blotvard wrote: Maybe a bad batch of 4049s? I got a couple of 4049UBE from eBay and one of those worked first off, after doing loads of unnecessary stuff. If that doesn't do it, try replacing IC1, 2 & 110. Otherwise, you will need to trace all the paths above to see if there is a short which is pulling the MCU pins.

I have the same issue! May I ask which 4069UBE you bought from eBay? I have two from Texas Instruments (Tayda) that don't work.

I had the same issue with ones from Tayda not working in my Yocto. I swapped them out for some new TI CD4049UBE’s from Digi-Key and those worked fine. I think there is an issue with the batch that came from Tayda.

Replaced with a new Texas Instruments CD4049UBE I bought from Conrad (Germany) and now it works!