Thread about the fun stuff I've had to debug over the past week and a half, working on modeling netlists of arcade sound circuits!
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1) A BJT intentionally being railed to +15V to force it into reverse junction breakdown, to use it as a white-noise source with a minimal number of parts. Had to HLE it using a uniform-spread white noise input node.
![[ColeJ]](https://pbs.twimg.com/profile_images/1043000626056065024/vDRPnUpt_normal.jpg)
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2) On a different board, a pair of XOR gates, with one as an inverter, looped back on each other, to form a cheap clock source for a CD4006 shift register, also looped back on itself to ostensibly form an LFSR. Had to replace the XOR-gate clock with a proper clock source.
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3) An Atari schematic that listed a resistor value as 330-ohm in the Bill of Materials (BOM), but 330K-ohm on the schematic. The BOM was wrong. Using a 330-ohm resistor turns the intended band-pass filter into a brick-wall all-stop. Not terribly useful.
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4) A schematic that listed two op-amps in comparator mode as having a positive input of +12V, which according to values couldn't possibly work. After finding the other two op-amps in the same package elsewhere in the schematic, found it was a double typo, should have said +2V.
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5a) A never-ending sound effect caused by incorrect modeling of the voltage drop on an op-amp, which assumed a reduction of 2V regardless of supply voltage, when it should have been 2V at +/-15V and less at +/-12V.
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5b) The output of that op-amp was fed into the threshold pin of a +12V 555 timer via a resistor. The end result was the threshold rising to about +7.95V, never quite reaching the +8V for shutoff. Solution: Separate LM324 model for a +/-12V source and 1.6V drop.
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