Utterly Befuzzled! Cannot get 9V out of my psu!

[brand0nized]

 

Trying to test my JMK Modular Delay, and the first thing I do is to take voltage at the +/- on the board, but I can only get about .4V. I'm using a 9V center negative psu from an old Zoom unit to test my effects.

I unplugged it and stuck my multimeter leads directly into the psu plug, and I can get 9V, but when I plug it into a DC jack with wires hooked up to the delay board, my multimeter only reads about .3-.4V.

Even when I plug it into my daisy chain box (1590a with a bunch of dc jacks daisy chained together), I can only read .3-.4V from all DC jacks including the one the psu is plugged directly into.

My last resort was to wire my board directly to the psu plug. I soldered wires to the board, and stuffed the negative wire into the center of the psu barrel with some foil. At this point, I tested for voltage, one lead on the board's ground, and another touching the outside +9V of the psu barrel. This reads 9V. But when I electric tape the positive wire from the board to the outside of the barrel and test for voltage on the board, again, only .3-.4V.

So it seems to me right now, I can't read 9V on my multimeter unless at least one of my leads are making direct contact with the psu plug barrel. When the 9VDC has to run through any wiring before it hits the delay board or a plastic DC plug, it will only read .3-.4V

WHAT IS GOING ON?!?!?!?!

[pickdropper]

Let me make sure I understand this correctly:

1.)  You measure 9V when the adapter isn't connected to any pedals.

2.)  Whenever you connect the adapter to the pedals (either directly or through the daisy chain) the voltage drops to 0.3V-0.4V.

Does it do this when connected to known good pedals or just the circuit you are trying to test?

If it does it with known good pedals, the power supply might be shot (or it's not really center negative).  If it is only with this modular delay, then I would check for shorts on the board and check to see if all of your components are wired with the correct polarity.

[brand0nized]

Let me make sure I understand this correctly:

1.)  You measure 9V when the adapter isn't connected to any pedals.

2.)  Whenever you connect the adapter to the pedals (either directly or through the daisy chain) the voltage drops to 0.3V-0.4V.

Does it do this when connected to known good pedals or just the circuit you are trying to test?

If it does it with known good pedals, the power supply might be shot (or it's not really center negative).  If it is only with this modular delay, then I would check for shorts on the board and check to see if all of your components are wired with the correct polarity.

Yup, you got it all right!

It works with my TS clone and Rub-a-Dub Deluxe pedal. I haven't measured voltage for them, but they both functioned properly daisy chained when I played with them this morning.

As for your last point, if there's nothing wrong with the power supply, shouldn't I still read 9V when I test the points on the board since they're wired directly to the +/- of the power supply?

The low read-out not only happens when connected to the delay board, but also when testing points inside my daisy chain box and also the pins of the DC jack which the power supply is plugged into directly.

Thanks for your input! I greatly appreciate it!

[pickdropper]

If there a short on the board, the excess current draw can drag down the voltage on your power supply.  If the board is plugged into your daisy chain, it would cause the same problem as if the power supply was connected directly to the board.

I would use your multimeter on the continuity setting and see if you have a short somewhere on the delay board.  Also check all your diodes, polarized caps and ICs and make sure they are facing the correct direction.

[brand0nized]

Thanks, I will check the board soon. But that still doesn't explain why I measure .3-.4v from inside the daisy chain box

[RobA]

Thanks, I will check the board soon. But that still doesn't explain why I measure .3-.4v from inside the daisy chain box

If you have a short or too much current draw in one effect, it can overload the power supply to the point where the power supply's output voltage will drop. The exact details of how much it drops will depend on the power supply design, but it sounds like yours is being knocked all the way to .3V. The reason you measure .3V or .4V everywhere is because that's what the PS is putting out when the board is connected.

[Willybomb]

If you have a short or too much current draw in one effect, it can overload the power supply to the point where the power supply's output voltage will drop.

Well, thanks for that.  I had/have an issue with a vero build of an Equinox II (so I got Haberdasher to etch me a board from Valvewizard's PCB layout) where I'd get 9v off my power supply, but as soon as it was hooked up to the vero, I'd get nothing at all measuring the vero where the +9v and ground wires attached.  A short was suggested but I couldn't find anything to save my life so it been relegated to the fail/maybe later bin

[brand0nized]

Thanks, I will check the board soon. But that still doesn't explain why I measure .3-.4v from inside the daisy chain box

If you have a short or too much current draw in one effect, it can overload the power supply to the point where the power supply's output voltage will drop. The exact details of how much it drops will depend on the power supply design, but it sounds like yours is being knocked all the way to .3V. The reason you measure .3V or .4V everywhere is because that's what the PS is putting out when the board is connected.

The strange thing about my situation is that I measure that low voltage even without my board connected to my daisy chain box. Just the psu into the daisy chain box with nothing else reads .3-.4V..

I'm suspecting my DC jacks could be defective. I started to notice the the center pin on my various jacks are at different heights (some are sunk into the jack more than others). I've also had one of my jacks start melting when I was soldering wires to it and the whole lug started wobbling around. Perhaps there's a short on the jacks also..

[Govmnt_Lacky]

The strange thing about my situation is that I measure that low voltage even without my board connected to my daisy chain box. Just the psu into the daisy chain box with nothing else reads .3-.4V..

If you are reading 9V out of your PS... then connect your daisy chain box and read .3-.4V then you have found your problem. AKA... the daisy chain box is dragging down the output of the PS.

Look for shorts/problems in the daisy chain box.

[brand0nized]

Thanks for the tip! I think there's also a short in my board because the same happens when I hook up the board directly to the psu barrel

[RobA]

What type of power supply do you have?

You were able to hook two known good pedals to the power supply via the daisy chain and this worked? But, when you hook the power supply to the daisy chain and measure the voltage (without the new PCB involved) it still measures near zero?

If that's the case, then it seems something more is going on, perhaps one or more of your cables has a short or one of the jacks is intermittent in its connections.

Some power supplies use buck converters that are sensitive and can go a bit crap before they go totally crap. It could be that too. Also, check your known working pedals again, because an IC in the power supply might have been damaged by having too much draw on it and the situation has changed since you tested with the known working pedals.