ICL7660S Falling output voltage?

[patrick398]

Hey guys,
Just built a Mutron III envelope filter which isn't working. I'm sure there are going to be MANY MANY issues with this build that are going to need working through but the charge pump seems like a good place to start.

The voltage readings i'm getting are wrong so i need to re-do that section but i thought before i do that i'd chuck it on the breadboard to check the chip. I'm getting a negative voltage out of pin 5 but it steadily declines when i read it with my DMM. Had a look on the forum and elsewhere but can't seem to find out why.
Here is the vero i'm using: http://tagboardeffects.blogspot.co.uk/2014/06/mutron-iii.html

Voltages on breadboard
DC Jack: 9.71v
Pin 1: 9.71v
Pin 2: 0.2v
Pin 3: 0v
Pin 4: 0.9v
Pin 5: -9.5ish and falling
Pin 6: 1.5v
Pin 7: 5.38v
Pin 8: 9.69v

Thanks

[Kipper4]

falling to ?
-18v? 0V? 9v?

[patrick398]

the rate of decrease gets progressively slower. Begins decreasing relatively quickly but then by the time it's down to -0.30v it decreases about 1mv every 5 seconds or so and then seemed to stop on -0.04v

[Kipper4]

I could be wrong but it seems like it's rising rather than falling.
Minus 9v to 0v   No?

Are all the caps orientated correctly?

[patrick398]

Yeah i was going to post another comment questioning whether it was rising or falling but didn't want to get sucked into semantics haha. You're right though, it's rising from -9v to roughly 0v. Pretty sure caps are oriented correctly; 100uf negative to pin 3, 10uf negative to pin 4, and 100uf negative to pin 5

[Kipper4]

And you have the jumper bottom row to pin 3?
Plus all 3 trace cuts?
Did you do any continuity check from the opposing sides of the cuts?
if there's a hair of copper left the trace cut wont work.
I despise vero. It might be worth running a blade across those trace cuts to be sure.

[patrick398]

Yeah jumper and all trace cuts are in place. I checked continuity on either side of each cut when i made them and also after i soldered the components in. Also checked continuity between rows for solder bridges but all seems fine which is why it's so confusing. I'm beginning to agree with you on the vero front. I'll do more continuity tests in the morning and report back.
Thanks for your help

[patrick398]

Continuity on the vero all checks out. What has me really confused is why it won't work on breadboard. Could it be a bad chip?

[bluebunny]

Have you got pictures of your breadboard we could look at?

[patrick398]

Sorry for the late reply, got caught up with a few things. So here's a picture of the charge pump on breadboard. Barring some calamitous oversight on my part i think it must be the chip. Everything else seems to be in order yet i'm still getting strange voltages. Pin 1 & 8 both have power via the jumper. 100uf from pin 1 to pin 3, 10uf from pin 2 to pin 4, 100uf negative to pin 5 positive to ground. Pin three jumpered to ground.

https://s10.postimg.org/lvgy5ktbd/photo_2.jpg

Here are the voltages:
Pin 1: 9.73v
Pin 2: 0.21v
Pin 3: 0.00v
Pin 4: 0.09v
Pin 5: 1.26v slowing falling (not even getting a negative voltage reading anymore)
Pin 6: 1.30v
Pin 7: 5.36v
Pin 8: 9.72v

I've tried this in various positions around the breadboard just to check it wasn't a dodgy bus or something. How can something so simple drive me so crazy!

[MrStab]

just for fun, what happens if you try putting a 10-100nF ceramic in parallel with the caps, or if you use lower than 100uF?
though that kinda relates to the initial problem, the nature may be different now if you're not getting any negative voltage at all.

[patrick398]

Tries a few different cap combinations but then i just get a flat 0.00v out of pin 5. Very confusing. I've ordered another chip from Tayda so maybe i'll just wait and see how that one behaves. This circuit is basically exactly the same as the test circuit on the datasheet so if this isn't working it must be the chip surely

[anotherjim]

I think the chip could be damaged. It's acting like it's not able to discharge the cap on pins 2 & 4 so it can't feed charge to the output. Will it do better if you add some load resistance across the output, say 1k?

When a project includes power generation, a fault elsewhere can damage the power supply when you fire it up.
I advise always isolating power supply/regulator sections from the rest of the circuit with a link that you place between the output of the supply and the feed to the rest of the circuit, so that you can verify the supply is working first with your meter, then add the link. Then don't fit any other IC's in their sockets until you can verify the supply is still ok measured at the respective IC socket pins.

[MrStab]

when you replace the chip, you should try it out on the breadboard first. then check everything connected to the positive and negative rails on the rest of the Mutron circuit for errors.

if it helps avoid the same situation, here's a list of do's and don'ts from the 7660S datasheet (C1 is the cap between pins 2 and 4, C2 is the cap connected to the negative output, VOUT is the negative output on pin 5):

1.  Do not exceed maximum supply voltages.
2.  Do not connect LV (pin 6) terminal to GND for supply voltage greater than 3.5V.
3.  Do not short circuit the output to V+ supply for supply voltages above 5.5V for extended periods; however, transient conditions including start-up are okay.
4.  When using polarized capacitors, the + terminal of C1 must be connected to pin 2 of the ICL7660S and ICL7660A, and the + terminal of C2 must be connected to GND.
5.  If the voltage supply driving the ICL7660S and ICL7660A
has a large source impedance (25Ω to 30Ω), then a 2.2μF capacitor from pin 8 to ground may be required to limit the rate of rise of input voltage to less than 2V/μs.
6.  If the input voltage is higher than 5V and it has a rise rate more than 2V/μs, an external Schottky diode from VOUT to CAP- (pin 4) is needed to prevent latchup (triggered by forward biasing Q4's body diode) by keeping the output (pin 5) from going more positive than CAP- (pin 4).
7.  User should ensure that the output (pin 5) does not go more positive than GND (pin 3). Device latch-up will occur under these conditions. To provide additional protection, a 1N914 or similar diode placed in parallel with C2 will prevent the device from latching up under these conditions, when the load on VOUT creates a path to pull up VOUT before the IC is active (anode pin 5, cathode pin 3)

http://www.intersil.com/content/dam/intersil/documents/icl7/icl7660s-a.pdf

[patrick398]

Amazing thank you guys! I'll let you know how i get on with the new chip. This was the first build where i thought 'you know what i think i'll just stick it straight in the enclosure before checking the circuits'...what a fool i was.
x

[EBK]

This was the first build where i thought 'you know what i think i'll just stick it straight in the enclosure before checking the circuits'...what a fool i was.

I do that with every build. 
Debugging a finished pedal can be a lot like intricate surgery sometimes, but that's the way I like it. 

(And now I've got that Ben Lee song, Catch My Disease, playing in my head...  )

[patrick398]

Right the new IC is here. Step away from the holiday brochures.
Breadboarded it, got -9.72v off pin 5 as expected. Soldered it all up, getting -9.72v on pin 5, but when i connect the wire from pin 5 to the main circuit board it rises to -6.82v. This has me a tad confused as surely these IC's should give out a constant voltage regardless of what you hook it up to?

[Kipper4]

But does it wah?

[patrick398]

Nah it does not wah. I'm sure there any many additional problems i'm going to have to work through, just wondering if it's a problem that Pin 4 on IC1 (top one) isn't getting -9v but -6.8 instead?

[anotherjim]

Assuming the normal +9v supply to the 7660 isn't falling also.

I don't think a charge pump chip like this can be regulated and deliver the same voltage as the input, albeit shifted to be a negative voltage relative to 0v.

Here's how it works.

Take a capacitor and charge it up to full voltage off a 9v supply then disconnect it.
Now the cap has 9v charge stored on it.
Now connect the + lead of the cap to 0v and measure the - lead.
It will be -9v.
If it only charged the cap to 8v, we can only expect -8v output.
The chip does this exact thing automatically, and repetitively to keep the output charge topped up.

But, anything taking current from the output is discharging the cap. If it discharges faster than it can be pumped back up, you will have less negative volts (or more positive negative charge if we want to do out heads in with semantics).

So, I suggest you look for any part of the circuit that is connected  to the negative supply that could be drawing too much current.
An op-amp -V supply  shouldn't take a lot of current.
A supply smoothing capacitor could be leaky or reversed.
A short somewhere.
A connection error. Easy to get 0v and -V connections mixed up when laying a board out - brain thinks both are negative & interchangeable.