Really confusing TC1044 inverter problem.

[slashandburn]

Sold a MK2 Tonebender clone (PNP, but with a TC1044 inverter) fella is having an issue with it that's really confusing me. Made quite a lot of pedals this way fwiw (probably over a hundred by now) and this was tested and working.

With a DC adaptor, LED lights up. No sound when pedal is turned on. With an external 9V battery adapter, No LED, but very low (far below unity) output.

At first I'm thinking I have an idea what's happened. My first theory: DC adaptor isn't regulated and the inverter fried (off the top of my head it's only rated for 10 or 11V) and the battery adapter he's using is the opposite polarity to the plug.

That's been shot down as the fella insists both the battery and the DC adaptor plugs are the same polarity. Which has left me completely baffled.

I've sent him some more TC1044 to try, but if just curious if anyone might have any other theories as to what might explain this, if both power sources he's using are indeed the same polarity.

[Govmnt_Lacky]

Just an initial idea:
If you used a switching DC jack in the build (so that battery power can be utilized when the DC wall power plug is removed) then maybe the power jack failed and is constantly providing the circuit with BOTH wall wart AND battery power. Thus... frying the TC1044.

[slashandburn]

Just an initial idea:
If you used a switching DC jack in the build (so that battery power can be utilized when the DC wall power plug is removed) then maybe the power jack failed and is constantly providing the circuit with BOTH wall wart AND battery power. Thus... frying the TC1044.

Ah sorry, should've mentioned, no internal battery at all,  DC sockets aren't switching.

[Govmnt_Lacky]

Ah sorry, should've mentioned, no internal battery at all,  DC sockets aren't switching.

If that's the case, I will go with "Used the wrong polarity DC wall wart" for $500... Alex

[slashandburn]

Ah sorry, should've mentioned, no internal battery at all,  DC sockets aren't switching.

If that's the case, I will go with "Used the wrong polarity DC wall wart" for $500... Alex

Yeah that would've been my first guess, except he sent a video of the issue, and made a point to show wall wart working fine in another pedal (I think a Keeley, red dirt or something). I'll check if he's okay with me sharing the video on here. The video doesn't show the battery clip being used on the Keeley pedal.

I think it's the ext. battery clip thats the wrong polarity, and the wall wart is putting out more than the 1044. It's the only way I can make any sense of it. But if they're the same polarity like he says, I can't explain the No LED but sound using one and LED but no sound using the other.

[Atodovax]

Sorry i though the pedal was working with the PSU and no LED. Could it be that he is trying with an exhausted battery? Did you test that the LED was working when you tested the pedal? Sometimes when you are used to solder the negative leg of an LED to the 3pdt and suddenly you have to do it the other way around, it could happen that you forgot about that. Also, did you power the LED in parallel to the effect or after the inverter? Because it might just be that he fried the 1044 but the LED is still working if its wired in parallel to the whole circuit. The fainted distorted sound that he is hearing could be signal bleeding through the circuit to the output due to leaky transistors even with no power or with the transistors being reversed powered. Im just thinking out loud...

[Rob Strand]

Get him to power the Keeley pedal with the battery adaptor.   Checking the simplest things first save a lot of hair pulling and crazy debugging thoughts.

Since the DC adaptor powers the Keeley pedal you would have to assume there is some problem with the Tonebender.

As a spin on Atodovax's comments maybe something is pulling a lot of current because the LT1044 is damaged.  The DC adaptor holds up under the heavy load but the battery voltage drops.   So different behaviour from same cause.

[anotherjim]

Keeley doesn't use full-wave rectifier DC input, do they?
Without a voltage test of the customer's PSU, You cannot be certain of much.

[aion]

Did you put a protection zener on the input before the TC1044? They have a max input voltage of 12V, and if it's exceeded even briefly they get fried. So it's basically mandatory to put an 11V or 12V zener at the DC input to ensure that there are no voltage spikes. Many 9V adapters are capable of putting out much more than 9V unless they're regulated and high-quality, so you don't want to leave this up to chance if you're building it for someone else.

[Nitefly182]

In some circumstances if the inverted output is pulled even a tiny bit positive on startup the chip will go to a fault state. Sometimes unplugging the power from the pedal and plugging it back in can fix this. IIRC there is a sample anti-latchup circuit in the datasheet that you can add to your design to prevent the inverted output from having this issue.

[slashandburn]

Thanks for all the pointers!

Just a quick update, I sent him some replacement TC1044, he popped one in the socket and it sprung to life.

Get him to power the Keeley pedal with the battery adaptor.   Checking the simplest things first save a lot of hair pulling and crazy debugging thoughts.

That was one of the first questions I asked him, no direct answer whether it actually worked on the Keeley, just an insistence they were both the same polarity. 

Oh well. All's well that ends well.