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I have an Artec QDD2 overdrive circuit and I recently powered it up with reverse voltage by accident and it doesn't give any sound on the stages of distortion, however it is allowing the bypass on selection. I believe the problem may be the ic that is on the board, its the only component that looks like it would get damaged by reverse voltage. I retrieved the smd code from the chip to be 33x1..... however when decoded seems to lead to nowhwere. I have attached a picture of the component and and hopefully someone turns up with the datasheet. ID like to know if it is damaged or if i must now go and attempt to find a seller of the exact ic or similar. I have attached voltage measurements as well. B+ being 9VDC. edit: I have drawn the circuit for a better look at what my problem could be.... I really just want this to be solved. enter image description here

enter image description here enter image description here

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  • \$\begingroup\$ Reversing B+ B- can be fatal. But without test measurements on IC p/n on every pin , how can we know? \$\endgroup\$ – Sunnyskyguy EE75 Mar 21 at 3:33
  • \$\begingroup\$ @SunnyskyguyEE75, that is where my uncertainty is.... I cant find the part online no matter how much i search and i would prefer to at least know what i have to measure. i know that when i measure between the B+ pin of the chip(what seems to look like it is the B+ of the pin) and the B- pin of the chip (this pin in directly connected to ground, i have no idea if my assumption is correct), i get a complete voltage drop of 9.35 V across the two. there are 3 other pins that all measure 0V when i check them. Also the chip has a 33x1 marking, 2 pins on 1 side and 3 pins on the other. \$\endgroup\$ – ForeverLearningJP Mar 21 at 19:41
  • \$\begingroup\$ What is the IC part number? datasheet link? is it this i.stack.imgur.com/8Nb5M.png \$\endgroup\$ – Sunnyskyguy EE75 Mar 21 at 19:44
  • \$\begingroup\$ Bookmark this SMD code search alltransistors.com/smd-search.php?search= Every OEM has unique codes for unique parts. Common parts are shared \$\endgroup\$ – Sunnyskyguy EE75 Mar 21 at 19:49
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    \$\begingroup\$ More likely it was forward current with B+.B- across the diodes instead of reverse biased until the AC signal with series RC distorts the peaks with 2nd+ 3rd order like vacuum tube soft clipping distortion \$\endgroup\$ – Sunnyskyguy EE75 Mar 22 at 2:26
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After hours of Pains-taking testing of the mysterious 33x1 IC, it turned out my problem was not there. In the schematic that i drew (https://i.imgur.com/gtqmTmb.jpg?1), there are two clipping diodes for the audio distortion. Notice that they are connected to B-, the reverse voltage was at first thought underestimated by me to have any effect on those diodes. After taking that look at the circuit schematic, i remembered, if i am getting no sound at all then i must have a short to ground along my signal path. The chip was not in my path, however those two diodes were. I tested each with my multimeter to discover that one diode's p/n junction died and caused the diode to forward bias both ways, resulting in the signal shorting out the variable resistor to ground.

Some food for thought could be that there was no damage caused by the reverse voltage..... maybe heat was to blame for this dead diode as a solder job was done on the variable resistor which is just millimeters away from the bad diode.

edit: I have found the IC for those who need that information. The datasheet for the LM321 IC is here http://www.ti.com/lit/ds/symlink/lm321.pdf . This IC matches all pinouts and amplification specs. Best part is all repairs on this circuit will always cost less than a new one on the market.

Keep learning everyone! Upvote this answer and question so people with similar problems know what to do.

Thanks to @Sunnyskyguy EE75 for all the bits of help that i got.

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    \$\begingroup\$ WTG , glad you did not give up!! \$\endgroup\$ – Sunnyskyguy EE75 Mar 22 at 2:29
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Hi ForeverLearningJP I have two of these QDD boards with problems, the early QDD has the same problem as yours had, it was returned to me from a luthier who was making an instrument for me and he stated it does not work (it did when I posted it as I tested it) I now think he reversed the voltage by mistake? please can you tell me which diode you used to replace as I cannot read mine. The second board a QDD2 has a loud pop when switched from bypass, Artec told me to look at C3 1uF and C1 0.1uF testing with 9v dc on and no input or output load, test input to ground for 0 vols and output to ground for 0 volts, if voltage is present replace the cap. my caps are fine so the problem lies elswhere? cheers Phil

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