7660s chip overheating

[John S]

Im building a fuzz dog Ampegulator and Im not getting any sound and the 7660s chip is getting really hot. It's giving me a loud hum. I have tried several 7660s chips. I have changed out the charge pump electrolytics and diodes.

[somnif]

Without a chip in, what is the voltage on pin 8?

(And Occam's razor check, you sure you have the chip in the right way around?)

[John S]

The chip is in the right way. Pin 8 reads 9.58 v.

[somnif]

Hmm, ok, if the input voltage is good then something must be drawing too much current through it. That's always fun to hunt down...

Lets see, with the chip in place, what are the voltages on pin 1 (may as well check for feedback) and the 9V and 18V pads next to the switch.
Check the voltages on pins 3 and 5.  3 should be 0, 5 should be negative input voltage (If I'm reading the datasheet right, anyway... I think.)
If you've got a continuity checker, make sure pins 6 and 7 aren't in the circuit (can be done with chip out).


The circuit to use the 7660 as a voltage doubler is simple enough that unless you've got a short or something the wrong way around I can't imagine the problem being in that section of the circuit. Should spit out (2*input voltage) - (combined Vf of diodes 4 and 5).

[John S]

Pin 1 = 9.58v
9v pad = 9.58v
18v pad = 16.67v
Pin 3 = 0v
Pin 5 = 3.7v
Pin 6 = 3.8v
Pin 7 = 3.9v

[John S]

Sorry Pin 5 = -3.7

[somnif]

Ok, another Occam's razor question, do you get sound through running in 9v mode? (you can leave the chip out).

Could also check the voltage on the drain pin on jfets 2, 3, 5, 7, and/or 8 as well (again, 9v mode should be doable without the chip in if things are working properly). Should all be pretty much the same.

[John S]

I did get sound at one point at 9v but it wasn't working properly. Ill measure JFETs today

[AntKnee]

I just built one of these, and I think it calls for a 1044 charge pump. IIRC, they function different from the 7660. You may need to jumper two pins to use the 7660. My memory is a bit smokey, so I'm not positive on all that, but may want to check it out.

[somnif]

The ampegulator BOM calls for a 7660, so I don't think that is the issue here.

If it wasn't working well in 9V mode then the problem likely isn't on that side of the circuit, and you instead have current going somewhere it ought not.

Any chance you have a ground error somewhere? Solder bridge, pot contact, anything of that sort?

[John S]

everything looks pretty clean. Still not sure what it could be.