Calling all TAPLFO experts, I am losing my mind!!! (Tap-Tempo Cardinal content)

[Cortexturizer]

Hi guys, major taplfo problems here :/ My tap tempo cardinal is sitting on my bench for a month as I am unable to get the LFO part working at all. Jon has been a great sport and helped me a lot to try and debug it but we came to a conclusion that  my TAPLFO is simply not working so I bought another one (ouch!). And that one isn't working either.

Basically I've got this thing on my breadboard



cause I am trying to get the LFO working but it ain't happening. It just won't oscillate. I bought one from Banzai Music and the other one from Musikding, both are from Germany. I bought my crystal from Banzai too. Could it be the crystal?

Here are my voltages for the LFO pins (depth at max, all other controls half-way up):

2 - 2.17 V
3 - 2.39 V
4 - 5.02 V
5 - 0.51 V
6 - 2.19 V (someslight oscillation from 2.18 to 2.21 but that's probably my multimeter)
7 - 2.18 V
8 - 5.05 V

The other taplfo chip I received shows 0.03 on pins 6 and 7.

It's a total mess. I can't believe this. Any thoughts guys? I would really like to finish this and put it on my board :/ some other tests I could do? Is it possible that I got 2 dead-on-arrival taplfos? I can't be that unlucky. I did not abuse them, they should be in good operational condition.

Thank you for any help you might provide. Cheers.

[midwayfair]

Just so everyone knows, this one has me stumped.

When you get a chance, maybe take a picture of the breadboard, but IIRC your voltages are identical between the board and the BB.

[madbean]

Have you tried connecting pin11 to ground via a 1k resistor? Pulling pin11 up to 5v might be making the rate too fast to detect. Just a guess.

[selfdestroyer]

I actually have one of these on my bench also that I am finishing up for a friend. I will take some reading from mine also if you like. I think I just need to put some pots on it and its ready to go.

When I was building one of Rolo's PCBs (Can't remember if it was my Twin Peaks or the liquid mercury) I had issues with my TAPLFO also. I knew the PIC was good since I programmed it myself and I was then able to read it and CRC check it to the HEX. It actually ended up being my crystal that I swapped out and mine came to life. I am not 100% sure if that was exactly fixed it but it is sure worth swapping out. I had a couple 20 MHz crystals that I had no idea where they came from so I ended up getting a bag of them from Tayda and they seem to unction just fine. I have built 4-5 TAPLFO pedals with out issues with them.

Hope you get it going man.

Cody

[m-Kresol]

I've got my taplfo chips programmed from uk-electronic, also from Germany. One of the crystals I also got there, the other one from tayda. Both seem to work fine.
Do you have a scope that you could try to measure the output with? might just be it oscillates but at too high frequency or too little depth. Frequency issues could be caused by the crystal for sure as it's the reference point.
good luck, it's an awesome pedal.

[Cortexturizer]

Thank you so much guys, the support means a lot as I am very discouraged by this :/ I am lusting for this pedal so will continue to put the effort for sure.

This is the crystal I use - http://www.banzaimusic.com/Quartz-Crystal-QM020.html

And no, I don't have a scope :/

@Brian, I will try that!

@Jon - I could send you a picture of my breadboard but I feel you will get a headache if I do! I used those probes and like 20 of them so the whole thing looks like a rat's nest, but since I am getting the same voltages like on the pcb I am guessing I have done it right.

[somnif]

I think a picture, however rats-nesty it might be will be useful.

So you are building the "Drum machine/sequencer clock" circuit, looks simple enough (which usually means "many possible routes to less than obvious failure")

"This example circuit provides tap-tempo +5V clock pulses for driving analogue sequencers or drum machines. R3 to R8 disable the waveform output (fixed to Ramp Up), the multiplier (fixed to x1), the output level (fixed to max), the pulse width (fixed to 2.5V, square), and the 'Next multiplier' input (tied high). The main LFO output isn't used. Tempo can be set either by the Tempo knob VR1 or by tapping the button."



I assume you're getting a good 5V in at pin1? (Pin 8 is the multiplier and showing 1x, so that looks fine.)
Does pin 4 zero out when you tap?
6 and 7 should be oscilating between 0 and ~2.5 when the thing is on, if its a constant reading it is possible its oscillating too quickly to read, I suppose.
Is pin 5 connected to anything?

[Cortexturizer]

I think a picture, however rats-nesty it might be will be useful.

https://drive.google.com/file/d/0B--6F_4JB7SYajM4amx0eEF0Qm8/view?usp=sharing
I don't think I can shoot this in a way that'll make it presentable :/ the crystal is on the left as I removed it from the pcb.

I assume you're getting a good 5V in at pin1? (Pin 8 is the multiplier and showing 1x, so that looks fine.)
Does pin 4 zero out when you tap?
6 and 7 should be oscilating between 0 and ~2.5 when the thing is on, if its a constant reading it is possible its oscillating too quickly to read, I suppose.
Is pin 5 connected to anything?

I do get 5V on pin 1.
Pin 4 zeroes out when I tap, yes.
5 is not connected to anything, on pin 6 I get 1.47V flat. Then I stepped away from the breadboard to have some lunch, got back, measured the voltages again and I was getting flat zeroes on pins 5,6,7. Now I can't even get 1.47 like before. Great. Just... great.

[somnif]

Whats up with the resistor off pin 7, it looks twisted around?

[Cortexturizer]

It's just warped like that as I couldn't push it into the breadboard socket easily, but it connects ok. It's a 1K for the LED, I tried it all without that resistor as well and it's the same as one would expect. It says 20.000 Mhz on my crystal, that's ok right? Just triple-checking, as I am desperate.

[somnif]

Ah I asked about the twist because I thought it might be shorting past the resistor straight to the LED.

How are you "tapping"? Is there a button off screen, or are you just tapping a jumper to ground? (I'm guessing its the blue wire slightly pulled out the ground rail but its 5:45am and I take nothing for granted at this hour)

Is the pinout on the trimmer the right way around? its a bit hidden behind some wires.

Lets see....

[Cortexturizer]

Hehe yes the blue wire hanging is the one that I tap to ground, and yes the trimpot is oriented correctly.
Feck it man, I just ordered a 3rd taplfo from a source from which Brejna confirmed it worked for him (same source Felix mentioned). If that one doesn't work Imma cry.

[midwayfair]

5 is not connected to anything, on pin 6 I get 1.47V flat. Then I stepped away from the breadboard to have some lunch, got back, measured the voltages again and I was getting flat zeroes on pins 5,6,7. Now I can't even get 1.47 like before. Great. Just... great.

Don't panic. It's not worse than before. Those are the output pins, they just show the voltage that the chip tells them to show.

The root problem is that it doesn't seem to be OSCILLATING. The actual voltages on those pins vary when the chip is working as it should. If something triggered when you weren't looking, they could have just gotten stuck at ground instead of stuck at 1.7V or whatever. So again, don't panic

You mentioned you pulled the crystal from the PCB -- did I missed that this was your only 20MHz crystal? I'm not sure how a crystal can get damaged or broken, but I'd absolutely swap it out. I've used the ones from Tayda without issue, though I think I would buy more than one or two of them just to be safe. I'd send you a couple but I have a feeling that shipping from Tayda or Banzai is a lot cheaper.

I had a look at the breadboard and despite the wires all over the place, I don't see anything amiss.

Ninja edit: Dude, don't order another TAPLFO. The chances of two of them being bad without trauma is extremely small.

[somnif]

I wonder if you could rent/borrow a DMM with a frequency meter for an hour or two somewhere. I know you can rent power tools at home depot, wonder if they have electrician supplies... Heck you can probably buy one for about the price of another LFO chip I bet. DMMs with it are about 15$ on Amazon, I'd wager a cheapo freq counter on its own would be about 10$... somewhere. 

Edit:

Ok lack of sleep is catching up with me, DMM freq testers cap out in the kilohertz range, not Mhz, duh. I shall keep thinking...

[somnif]

http://www.electronicecircuits.com/electronic-circuits/crystal-tester

If you have a bit of time on your hands you can try cobbling this together to see if your Crystal is still functional. If you dont have BC550s, 2N5088s would probably work just as well. If its working, LED lights. If no oscillation, no light.

edit: note may want to use a dim diffuse LED or up the ohms on R3 depending. Tossing in a waterclear with only 560 on the CLR would likely blind you....