DD-3 Debugging

[seten]

Schem:

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.synfo.nl/servicemanuals/Boss/DD-3T_SERVICE_NOTES_3rd.pdf&ved=2ahUKEwiuz4j-srHlAhVjhq0KHTdEBmEQFjABegQICRAB&usg=AOvVaw3Xm_se72gT9aGTaXwBxtSN

I followed the signal path with an audio probe and got to pin 1 of IC1A - theres audio on pin 2 but the pin 1 node has nothing. I'm really not sure what this means - at first i thought IC1 was the issue but since R14 connects pins 1 and 2 i figured some signal should be getting through that path. Then I thought something is shorting the pin 1 node to ground but nope its 0.87V above ground.

Whats my next step? I checked to make sure Q5, Q7, and Q9 were getting 9v and checked for continuity on R14 and C8 w/ pins 1 and 2 of ICA but I wasnt sure what to check after that.

(I wasnt sure if I should have added this in with my last thread but since that was a specific question I thought id make this for as I generally go through the debugging.)

[willienillie]

Then I thought something is shorting the pin 1 node to ground but nope its 0.87V above ground.

Shouldn't it be ~4.5V?  I could be wrong because I'm an idiot, but if not I'd be suspicious that maybe C30 or C31 was shorted, or maybe IC1 could be shorted internally.

Does the pin1 voltage change when in bypass?  With Q2 open you can rule out stuff past that.

[Slowpoke101]

Measure the voltage on pin 3 of IC1. It should be close to 4.5V (the DC voltages on pins 1 and 2 should also be at 4.5V).
You will most likely find that the voltage is close to 0V. If this is what you find then you may have to prepare to replace IC1 - being a surface mount device you may not find this easy.
IC1 seems to have a higher failure rate than what's usual.

[seten]

Then I thought something is shorting the pin 1 node to ground but nope its 0.87V above ground.

Shouldn't it be ~4.5V?  I could be wrong because I'm an idiot, but if not I'd be suspicious that maybe C30 or C31 was shorted, or maybe IC1 could be shorted internally.

Does the pin1 voltage change when in bypass?  With Q2 open you can rule out stuff past that.

I mustve made a mistake last night, but dont think itll change anything. I'm getting 1.1V on pin 1 on and bypassed. Does that mean I can rule out anything past Q2 or the opposite, and either way could you explain why to me for future reference?

Measure the voltage on pin 3 of IC1. It should be close to 4.5V (the DC voltages on pins 1 and 2 should also be at 4.5V).
You will most likely find that the voltage is close to 0V. If this is what you find then you may have to prepare to replace IC1 - being a surface mount device you may not find this easy.
IC1 seems to have a higher failure rate than what's usual.

I'm getting 1.1V on pin1, .87V on pin 2, and 1V on pin 3. Does this mean IC1 needs replaced for sure or is there any other things I could check before I try to tackle replacing it?

[vigilante397]

So I should have jumped on this earlier, but I have a working DD-3 that on my workbench, are there any voltages you want me to get for you before I send it back to the owner?

[willienillie]

I'm getting 1.1V on pin 1 on and bypassed. Does that mean I can rule out anything past Q2 or the opposite, and either way could you explain why to me for future reference?

Q2 acts as a switch for the byapss system, so when it's "open" it's like there's no connection to whatever follows.

[seten]

I'm getting 1.1V on pin 1 on and bypassed. Does that mean I can rule out anything past Q2 or the opposite, and either way could you explain why to me for future reference?

Q2 acts as a switch for the byapss system, so when it's "open" it's like there's no connection to whatever follows.

Okay, so on Q2 pin 2 is the input, pin 1 is the output, and pin 3 is somehow connected to the bypass system? So if I understand correctly youre saying since im getting the wrong voltages regardless of if its bypassed or not, that means that it cant be anything connected to pin 1 thats causing the issue because when its bypassed pin 2 is unconnected to pin 1.

So I should have jumped on this earlier, but I have a working DD-3 that on my workbench, are there any voltages you want me to get for you before I send it back to the owner?

I appreciate it, but I'm really not sure what to even ask for. I think IC1 is definitely showing the wrong voltages, the only question now is if its IC1 itself or something past that - it cant be anything past Q2 but it could be anything in the Q5 - Q7 - Q9 region or past that. If you have any suggestions for voltages i could check to determine between those two options that would be greatly appreciated though.

[Slowpoke101]

IC1 is the most likely suspect. However further investigation is warranted.
Pins 3 and 5 of IC1 are connected to the Vref (virtual ground ) rail which should be at about 4.5V DC. This voltage is produced by the voltage divider formed by the resistors R63 and R59. This voltage is "filtered" by C46. Find C46 and measure the voltage across it. You will most likely find that it is well below 4.5V so remove power and measure the resistance across R63 (10K ). With R63 still connected to the rest of the circuit it will measure lower than 10K (about 4k5 ) if R63 is OK.

The next step is to isolate pins 3 and 5 of IC1 and then see if the voltage across C46 rises to 4.5V
If it does rise then IC1 is toast and needs to be replaced. If it does not rise then further investigation is required.

[vigilante397]

Do you have the means to swap IC1? It doesn't necessarily have to be a M5218AFP, but a TL072 or 4558 or whatever dual opamp you have available. That would be a quick way of finding out if that's the problem, and even if it doesn't fix it a different opamp won't hurt anything.

[seten]

Got it! It was IC1. Okay, part 2, I have another broken DD-3, I'm a little more scared of this one. IC1 seems to be working, nice and strong on pin 1, then weakened by R13 and seems to be the same weak and dry signal on the output. the LED works but the switch doesnt affect the signal at all at any point as I was audio probing it. What can I check next? Wheres the point where the delay signal should be mixed back in with the dry and shouldnt the dry signal be amplified back to the original volume at some point?

EDIT: Pins 3 and 5 of IC1 are indeed around 4.5V but 1 and 2 start at less than 1V and just constantly fall slowly. I'm guessing this is a problem. Would that be IC1 again or something else?

[seten]

I'm getting 1.1V on pin 1 on and bypassed. Does that mean I can rule out anything past Q2 or the opposite, and either way could you explain why to me for future reference?

Q2 acts as a switch for the byapss system, so when it's "open" it's like there's no connection to whatever follows.

I noticed that on my second broken DD-3 I'm getting the same signal audio probing either side of Q2 whether or not the switch is bypassed or not, so I thought then Q2 was the issue, but then I realized if Q2 didnt pass signal when the pedal was bypassed, how else would the dry signal get to the normal output? Obviously it will still be able to go to the direct dry out since that signal path split off is before Q2.

[seten]

IC1 is the most likely suspect. However further investigation is warranted.
Pins 3 and 5 of IC1 are connected to the Vref (virtual ground ) rail which should be at about 4.5V DC. This voltage is produced by the voltage divider formed by the resistors R63 and R59. This voltage is "filtered" by C46. Find C46 and measure the voltage across it. You will most likely find that it is well below 4.5V so remove power and measure the resistance across R63 (10K ). With R63 still connected to the rest of the circuit it will measure lower than 10K (about 4k5 ) if R63 is OK.

The next step is to isolate pins 3 and 5 of IC1 and then see if the voltage across C46 rises to 4.5V
If it does rise then IC1 is toast and needs to be replaced. If it does not rise then further investigation is required.

For future reference how do you isolate individual pins on an IC? Do you just mean by cutting the trace to them?

[vigilante397]

For future reference how do you isolate individual pins on an IC? Do you just mean by cutting the trace to them?

No! Lifting the pin out of the pad. Lifting a pin means worst case scenario you brean the pin and the IC needs o be replace. Cutting a trace means worst case scenario you've ruined the board. Avoid damaging the board wherever possible.

[seten]

For future reference how do you isolate individual pins on an IC? Do you just mean by cutting the trace to them?

No! Lifting the pin out of the pad. Lifting a pin means worst case scenario you brean the pin and the IC needs o be replace. Cutting a trace means worst case scenario you've ruined the board. Avoid damaging the board wherever possible.

Ahhh so just desoldering a pin and bending it up a bit with tweezers?

[vigilante397]

Ahhh so just desoldering a pin and bending it up a bit with tweezers?

Yup, exactly that.