Broken Boss DD-3

[Storky]

Hello,

My name is Steven and I've recently started to get into pedal building.
I haven't gotten beyond making a simple distortion so far, so I don't have a lot of experience.

Recently I bought a boss DD-3 for €10 that was listed as only giving out a clean signal, so I assumed just a loose wire on the main output of something.
Boy was I wrong, as far as I can see, everything is connected and should be working.
The model is made in Taiwan, most components are surface mounted except for capacitors, and a long 14 pin chip (IC3).

I've followed trough various posts on various forums, but they all end up solved or dead ends, with the measurements mentioned never quite matching my own.

Using an audio probe I can hear a clean signal in various places, but never a delayed one, no matter the settings of the controls.
As far as measuring voltages that I wrote down from following another post, i get the correct +9v at pin 14 of IC3, +5v at pin 14 of IC4, but only +0.8v at pin 3 of IC1 (this should be +4.5v)
This post then goes on saying there is likely a short in the +9v net, and to check C1, C11, wich are fine for me. And feel if IC2 of IC3 get hot, wich mine don't.
Then it says to start cutting traces to isolate the short, wich is way over my head.

Does anyone have any alternate input on anything else I can look for?

[Slowpoke101]

Welcome to the forum. Hopefully we can help you out.

From what you have found so far, the 0.8V found where 4.5V should be is the most interesting.
See if you can locate C23 (47uF 6V). It is most likely a tantalum capacitor and not an electrolytic. De-solder one of its legs (so it is isolated from the circuit) and retest for 4.5V. If the voltage is now correct just replace the capacitor and then see what else isn't working.

Make sure that you have a good copy of the DD-3 schematic and component overlay otherwise you will get very confused with this device.

[Storky]

Thank you.

Unfortunately, with or without that capacitor i'm getting 0.9v instead of 4.5v still.

[Slowpoke101]

OK. Now having followed my own advice, I have obtained the correct schematic and component overlay for the SMD version of the DD-3 

Back to the 4.5V rail. The capacitor of interest is C46 (47uF 16) - Most likely an electrolytic. Take it out and then re-measure for 4.5V
If it is still not present, locate R63 (10K) and measure the voltage on one end and then the other. One end should be 9V and the other should 4.5V (or the voltage that you measured before). If you have 9V on one end, power down and measure the resistance of R63. It should be 10K.
R63 is very close to D9 which is a reverse power protection diode. This diode can overheat and damage parts near it if it has done its job - somebody plugged in the wrong power source. Normally the diode has to be replaced so check around that area just in case someone did blow the pedal up and replaced the diode in a manner that would be considered as butchering.

It's a bit odd that you are getting clean (dry) audio through the pedal as 4.5V is also used by the audio switching FETs. Does the pedal respond to the foot-switch (LED goes on and off)?
Does the pedal allow bypass audio through as normal?

[Storky]

I have desoldered 1 leg of the C46 (still left the previous C23 unsoldered on 1 leg as well)
I now get 9v from one side of the R63 resistor, and 0.9v from the other side.
measuring its resistance after disconnecting the power gives me a reading of 5.95 with my multimeter set to 20k.
Other resistors around there that look the same to me do indeed measure 9.9 or 10 at the same setting (R52, 38 and 37 for example)
The pedal does respond to the foot switch, led goes on and off, and the hold function also works when i put it in that position.
the direct output works as normal, the regular output has no signal at all.
only with an audio probe i get a dry signal from IC3 (the sound here is very noisy, audio being quiet with a lot of interference) and from IC1 (this sound is quite clear, but not necessarily louder then the input i think)

I took some pictures to make sure i'm measuring in the right place.
in the first picture I measured the top of the tiny 2 resistors (reading 103 upside down).

The second picture is to show the one area on the back of the PCB i'm not 100% sure of if there is something bad going on.
This is where the AC plug connects to, that bottom L shaped connection just looks odd to me, with a little black spot on it. could just be random dirt?

[Tony Forestiere]

The second picture is to show the one area on the back of the PCB i'm not 100% sure of if there is something bad going on.
This is where the AC plug connects to, that bottom L shaped connection just looks odd to me, with a little black spot on it. could just be random dirt?

The colloquialism "Fugly" comes to mind. I think you've got this one.

[Storky]

The colloquialism "Fugly" comes to mind. I think you've got this one.

You mean this would likely be the big problem part?
If so, would re-soldering this joint be a fix?
I'm assuming the jack itself is not damaged since i'm still able to run it on AC power.

[Slowpoke101]

The very bad soldering on the DC power jack is not good. You should resolder and clean up the area. The main 4.5VDC track runs close to the jack and may have an unwanted resistance connection to one of the jack's pins.



Fully remove C46 and check the resistance between the C46's terminal pads on the circuit board. You may see a reading near 1K. It should be higher than this but the fault condition may bring the value lower than what it should be.
In the picture below I have marked the components connected to the 4.5V rail. Most are resistors and it would be very unlikely that they or where they are connected could drag the 4.5V rail down to 0.9V



Check the areas around these parts carefully and make certain that there is nothing that may cause a short circuit (stray bits of wire, splashes of solder). Clean up anything questionable.

The most likely cause of the 4.5V rail being low at 0.9V is IC1. Are you up to trying to replace it?

[Storky]

I'll have a look at cleaning up and resoldering the AC jack, and measuring the resistance where C46 fits.
I've never tried to do any SMD soldering, and I even got a bridge or 2 when soldering on perf board for my homemade pedal, those traces are miles apart compared to the ones on IC1!

But if cleaning up does not fix anything, i won't loose anything by trying, the pedal is essentially useless as it is right now.

[roseblood11]

You measured 9V on the pcb. How could resoldering the dc jack solve your problem?

[DIY Bass]

I recently had a similar problem on a pedal I was repairing.  The 4.5V line was shorted to ground (or nearly).  I first of all removed the filter cap between ground and 4.5V to see if that was the problem.  It wasn't.  Next I traced through the entire 4.5V live to see if there were any other components that connected from 4.5V to ground.  Turned out that there was a pot lug that was connected to the 4.5V live that was also shorting to the case.  In your shoes I would do the same thing - physically inspect the entire 4.5V trace on the board to see what it connects to.

[Storky]

In your shoes I would do the same thing - physically inspect the entire 4.5V trace on the board to see what it connects to.

I am wholly inexperienced when it comes to PCBs, and following schematics on this level.
I've got the repair manual wich shows a detailed image of the components, the bare PCB with just the traces, and the actual schematic drawing, so in theory I should be able to trace everything.
Its just that in practice, i've not done more then build a 'bazz fuss' type super easy circuit on perf board. I was real proud when i added a diode selector switch, and a volume pot to that.

[Storky]

Everything is clean, i can't see anything wrong on the smd side at all.
The points you marked on the rear end were just surface dirt, a bit of a crusty layer that wiped right off with some alcohol.
the resistance over the C46 pads is 6k.
When i measure the resistors you marked as components being on the 4.5v rail i get 90k at R58 and R62, 6K at R63 anr R59 and 1M over R60.
The lower resistance values are just because they are stil in the circuit togeather i take it?

[Storky]

Quick update, after googling some more about too low of a voltage on the 4.5v rail, I came across https://www.diystompboxes.com/smfforum/index.php?topic=116442.0. Exact same issue.
I disconnected pin 5 and 3 of IC1 and wouldn't you know it, measuring 4.35v on the 4.5v rail. I'm assuming the slightly lower voltage is because my battery has been slowly dropping in voltage, down to about 8.6v now.
I'll take it this means IC1 is broken and I'll have to figure out a way to replace this tiny thing?

[Slowpoke101]

It certainly looks as if IC1 is faulty.
Replacing it would be the next step.

I sent you a PM (personal message) a few days ago covering this subject.

[Dasher]

Did Boss get a bad batch of opamps?

I recently purchased a non-working DD3 with the same symptoms as Storky's; the direct output worked fine but the effect output did not. Using an audio probe I quickly discovered that the signal was being lost at IC1. I took some voltage measurements of IC1 and found a vref of 0.9V on pins 3 and 5, just like Storky. I lifted pins 3 and 5 from the traces and sure enough, my vref increased to 4.8V. I haven't replaced IC1 yet (I don't have any smd opamps  in my parts bin) but I'm optimistic that replacing it will fix the pedal.

Does it seem odd that multiple people have had the same (or at least similar) problem with a part that, as far as I can tell, is unlikely to go bad?

[Dasher]

Just thought I'd follow up on my previous post in case someone else encounters a similar issue. I replaced IC1 and it fixed the problem.