Tonepad CE-2 Trouble Shooting

[plndrm]

Hi,
After using the search button and a lot of reading I can't nail down the issue I'm having with this build.  It is my seventh pedal build, and the first to As the subject says its a tonepad's ce-2 build and I'm not getting any chorus effect in the output, it is passing a clean signal through the board but the IC's are not oscillating. 
I built a tonepad small clone last month and it works great.  So I pulled the MN3007 from the ce-2 build and stuck it in the small clone and it is working properly. Had a few 4588's and I stuck them in the circuit and still nothing, I don't have anymore TL072's so I stuck a 4558 in that location still nothing.

Link to build doc: http://www.tonepad.com/getFileInfo.asp?id=101
Here are my measurements of the IC's and the five 2N5088's with both B100k pots set and measured at 50K:

IC1-JRC4558
1) 4.65V
2) 4.66V
3) 4.64V
4) 0.3mV
5) Between 2.209V and 7.11V depending on the position of VR3 trimpot.
6) 4.65V
7) 4.65V
9.33V

IC2-TL072
1) 4.73V
2) 4.60V
3) 3.81V
4) 0.3mV
5) 4.60V
6) 4.68V
7) 3.387V
9.33V

IC3-MN3007
1) 9.24V
2) 4.77V
3) 3.90V
4) 0.620V
5) 0.3mV
6) 4.73V
7) 3.469V
3.471V

IC4-MN3101 ***Came from EvilBay*** SmallBear was out of stock prior to 1-Dec-21.  Pin 8 is outputting the correct voltage (1-(14/15)).
1) 9.24V
2) 4.73V
3) 0.3mV
4) 4.78V
5) 325.6mV
6) 8.26V
7) 2.979V
0.620V

2N5088's
1: E-3.60V, B-4.04V, C-9.33V
2: E-3.91V, B-4.46V, C-9.33V
3: E-3.69V, B-4.16V, C-9.33V
4: E-2.952V, B-3.481V, C-9.24V
5: E-0.3mV, B-357.4mV, C-7.84V

I reflowed everything, found a lifted pad on one of the pots, it is visible in the 6th picture, but continuity still exists. Also didn't see any solder bridges under the magnifying lens.
Here are a few images of the board if it helps.














Thanks in advance for any help/suggestions where to go next.

Marc

[ElectricDruid]

Welcome pindrm!

There's nothing obviously wrong with any of the soldering, and I can tell you've done this before! Looks pretty good. Both the op-amp and the transistor voltages look ok at first glance, so I'd have to say that the clock chip is suspect, although there are still other possible causes too.

Swapping the 3007 into another circuit to test it was a good idea. Do you have *anything* else that uses a 3101?!?

The VR3 trim will need to be in a mid position for the BBD to work, but it looks from your voltages like you had it set at roughly 4.5V and I'd have thought that was close enough. You could try pulling the 3101 and 3007 chips out of their sockets and testing for continuity on the clock signals (pins 4 to 2, and 2 to 6) but I suspect those are fine. You could also check to see if you can see the LFO oscillating on IC2 pin 7. It'll be easier to see on the meter with the rate as slow as possible. It should be wobbling about. If it's not, that might prevent the clock from running and disable the BBD.

[Govmnt_Lacky]

Recommend swapping out IC2. Take out the TL072 and use another dual op amp that is more suitable for an LFO. Try a TL022, TL062, or possibly another JRC4558. TL072 is not really a good IC to use for the LFO.

[plndrm]

Wow thank you for the quick responses. Did some additional probing about...

Swapping the 3007 into another circuit to test it was a good idea. Do you have *anything* else that uses a 3101?!?

Unfortunately I do not have any other way to test the 3101's, I wish I did.

The VR3 trim will need to be in a mid position for the BBD to work, but it looks from your voltages like you had it set at roughly 4.5V and I'd have thought that was close enough. You could try pulling the 3101 and 3007 chips out of their sockets and testing for continuity on the clock signals (pins 4 to 2, and 2 to 6) but I suspect those are fine. You could also check to see if you can see the LFO oscillating on IC2 pin 7. It'll be easier to see on the meter with the rate as slow as possible. It should be wobbling about. If it's not, that might prevent the clock from running and disable the BBD.

I have continuity between both sets of pins and I do not see any drift in the voltage on pin7 of IC2 with either the TL072 or the 4558 installed.  I probed it with my old Agilent scope and didn't see any wobble different then the other pins.

From the start I've been able to hear what sounds like the 3007 starting up when the trim pot is just a little past half way.  I read in another post on there that right before the sweet spot the signal will distort, I'm hearing the distortion right around the mid point of the pot.
I did the blend and vibrato mods, when R21 is taken out of the circuit (vibrato mod ON) the output level drops significantly if the blend pot (C250K) in series with R22 turned all the way counterclockwise (RT=47K+250K).  Don't know if that helps debug or not.

Finally here are the measurements of IC2 with the 4558 installed:
1) 5.48V
2) 4.66V
3) 5.00V
4) 0.55mV
5) 4.69V
6) 4.85V
7) 4.67V
8. 9.33V

[ElectricDruid]

Unfortunately I do not have any other way to test the 3101's, I wish I did.

Pity, but that's what I guessed.

I have continuity between both sets of pins and I do not see any drift in the voltage on pin7 of IC2 with either the TL072 or the 4558 installed.  I probed it with my old Agilent scope and didn't see any wobble different then the other pins.

Ok, that sounds like a solid result. So it looks like the LFO isn't working. If you can get your scope on pin 7 of IC2, you should be able to see the LFO oscillating - and we're talking about a triangle wave signal of several volts up and down, so this isn't something you can easily miss or mistake for something else. Either it's there or it's not.

From the start I've been able to hear what sounds like the 3007 starting up when the trim pot is just a little past half way.  I read in another post on there that right before the sweet spot the signal will distort, I'm hearing the distortion right around the mid point of the pot.

I did the blend and vibrato mods, when R21 is taken out of the circuit (vibrato mod ON) the output level drops significantly if the blend pot (C250K) in series with R22 turned all the way counterclockwise (RT=47K+250K).  Don't know if that helps debug or not.

That sounds about right. The blend pot lets you adjust the amount of wet signal going to that final mixer, so tweaking it lets you turn down the wet signal. If you've got the vibrato switch open (hence removing the dry) then the blend control is basically a volume control for what's left!

Finally here are the measurements of IC2 with the 4558 installed:
1) 5.48V
2) 4.66V
3) 5.00V
4) 0.55mV
5) 4.69V
6) 4.85V
7) 4.67V
8. 9.33V

Well, the LFO op-amp looks happy to me. So if it's not oscillating, it's not because the op-amp is bad. The LFO bias voltage (pin 2 and elsewhere) looks fine, so that rules out R33/R34/C20. I'd check the Rate pot connections and R31, the integrator cap C19, and (of course) double-check values around the LFO.

[plndrm]

So it looks like the LFO isn't working. If you can get your scope on pin 7 of IC2, you should be able to see the LFO oscillating - and we're talking about a triangle wave signal of several volts up and down, so this isn't something you can easily miss or mistake for something else. Either it's there or it's not.

I left the 4558 IC in the socket so the first to measurements with it installed.  (I didn't think to measure Delta-Y until I installed the TL072)
Both Pots at full Counter Clockwise:

Both Pots at full Clockwise:

There's some clipping in the waveform with the 4558 as seen.

TL072 at full Counter Clockwise:

And full Clockwise:

Well, the LFO op-amp looks happy to me. So if it's not oscillating, it's not because the op-amp is bad. The LFO bias voltage (pin 2 and elsewhere) looks fine, so that rules out R33/R34/C20. I'd check the Rate pot connections and R31, the integrator cap C19, and (of course) double-check values around the LFO.

I'm going to go over every resistor/cap value again, starting with those mentioned.

Picked up the scope to recap the two tonewheels in my Hammond E and I haven't the space to do the job properly, so please excuse my measurement techniques, the manual isn't the greatest read.

Thank you.
Marc

[plndrm]

I do have a DOD FX68 Super Stereo Chorus that I purchased new in 1995 with a MN3101 in it...

[Slowpoke101]

It would be best not to attack the working DOD unit just yet when a few more 'scope checks could be useful. So far your test show the LFO appears to be quite happy which is good. Nice 'scope by the way. One of your previous posts you mentioned that when R21 was out of circuit (Vibrato Mod - no dry mix) the output level was somewhat lower. This could be of interest as it could mean that the 3007 isn't biased correctly or it isn't being clocked correctly. Check the waveforms on pins 2 and 6 of the 3007 and see if there if there is a square-ish wave there (I forget what frequency but it does vary with rate). If it isn't there, the 3101 is toast. If it is there, the bias is out and it needs adjustment. Adjusting the bias is an exercise in extreme patience. If your have checked out other threads you may have read some of mine as well. The sweet spot on the trim-pot is extremely narrow and very hard to actually find. But is it best to adjust with R21 out of circuit. Once you find the spot, you adjust for best volume with the least distortion.

One other thing when building effects - get it to work first and then do the mods. The mods can confuse remote debugging efforts. That's why why I took a while to make some suggestions. I do apologise.

Good luck and please let us know how you go.

[ElectricDruid]

Both Pots at full Counter Clockwise:

You've got a good scope and can look at the signals at various points in the circuit! That's great and is going to make life a lot easier and debugging a lot quicker.

But first - 66KHz on an LFO?!? What's going on here?! Cap value wrong by several orders of magnitude? R32 value out by a mile? Something is way out.

[antonis]

But first - 66KHz on an LFO?!? What's going on here?! Cap value wrong by several orders of magnitude? R32 value out by a mile? Something is way out.

I think 15μs should be 15ms, Tom..

[Kevin Mitchell]

But first - 66KHz on an LFO?!? What's going on here?! Cap value wrong by several orders of magnitude? R32 value out by a mile? Something is way out.

I think 15μs should be 15ms, Tom..

How is the scope's time division relevant to the measured frequency?
Serious question. I'm confused 
oOOF. Nevermind. Didn't know what I was looking at.

Anyways,
It does seem like that LFO is singing. Making it no longer an LFO.
Connect it to the output! We've got a noise maker on our hands.

[ElectricDruid]

But first - 66KHz on an LFO?!? What's going on here?! Cap value wrong by several orders of magnitude? R32 value out by a mile? Something is way out.

I think 15μs should be 15ms, Tom..

So why isn't it? 

[Slowpoke101]

Good eye Tom. Wish that I (pun intended) had noticed. 66KHz is a little bit too fast for a LFO for most people's tastes. C19 is the first item of interest. It should be 0.1uF but it most certainly worth checking all the component values in the LFO just to be certain that no errors crept in during construction.

[plndrm]

Good eye Tom. Wish that I (pun intended) had noticed. 66KHz is a little bit too fast for a LFO for most people's tastes. C19 is the first item of interest. It should be 0.1uF but it most certainly worth checking all the component values in the LFO just to be certain that no errors crept in during construction.

Yes excellent eye!  I missed it, it was difficult keeping the probe on pin7 and snapping a picture on my phone at the same time.  It's the first time in twenty years that I wish I had a floppy drive for my laptop. 

I pulled both C19 and R32, they measured 104.3nF and 993.7Kohms respectively, both well within spec... But what I found was a lifted trace on one of C19's legs, and sure enough no continuity between C19 and pin7 of IC2 and pin1 of VR2 (Depth Pot). 

Soldered a small jumper between C19 and Pin1 of VR2.  BOY WHAT A DIFFERENCE THAT MADE!  Hooked up the scope and now I can see the voltage SLOWLY rise and fall, so slow that I can't figure out how to capture the waveform. 
Plugged in my "old" Strat Plus and YES!

We have a chorus!  The trim pot was pretty close to where it needed to be, had a little distortion on the low end that a few degrees clockwise fixed.

Thank you everyone for your help!
Now to powder coat the 1590BB2 enclosure.

Marc