The Case Of The Contrary Capacitor. WTF Happened?Posted: February 17, 2013
I need your help in solving a mystery. I think I solved it, but it seems too ridiculous. Actually, if what I think happened did happen, it would be downright messed up. Please look over the following evidence and exhibits and let me know what you think. I am hoping I am wrong and that someone can shine some light on a very logical explanation that I have overlooked.
Exhibit A – The Carl Martin Hot Drive’n Boost mk3
- I purchased this pedal brand new in the summer of 2004. Before buying it, I tested it through several amps with a variety of guitars. The pedal sounded great and had no abnormal buzzing or hums–even with the gain maxed.
- I used this pedal for the next three years. It has seen many gigs, was used on several recordings, and racked up hundreds of hours of home use. During this time, the pedal functioned flawlessly.
- I got a new overdrive pedal and the Hot Drive’n Boost wasn’t being used much so I decided to post it on an auction website.
- Before posting the pedal, I gave it a thorough inspection. I checked for scratchy pots, dirty jacks, proper switch operation, and listened for any weird noises.
- The pedal checked out fine and was posted up for auction. It sold five days later and was shipped the next day.
The Return Of The Pedal
- I received a message from the buyer within a week of shipping it stating that the pedal was unusable due to a loud buzz.
- My return policy stated, “Returns will only be accepted if the item is received as defective or not as described. No returns will be accepted on items just because you didn’t like it.”
- Since the pedal appeared to be defective, I returned his money and he shipped back the pedal.
Exhibit B – The Buzz
- After receiving the returned pedal, I plugged it up and heard the buzz. see Exhibit B
- I was too busy to take the pedal apart to inspect it and ended up putting it in my closet, were it was eventually forgotten.
Fast-Forward Five Years
- I opened up a mystery box I found in my closet and found my forgotten Hot Drive’n Boost mk3.
- I plugged it in and the buzz was still there. Apparently, I don’t have magical closet gnomes that like to fix shit.
- After opening the pedal I saw a yellowish splatter on the inside of the lid. The yellowish splatter was adjacent to a blown smoothing capacitor in the pedal’s power supply. see Exhibit C
- The buzz was ruled as an effect from the blown capacitor.
First Attempt To Repair
- I was able to locate a new 470uf 35V electrolytic capacitor at a local electronics store.
- I replaced the bad capacitor–paying special attention to the direction in which the original cap was mounted due to the capacitor being polarized and knowing that if I put it in wrong it would blow again.
- After reassembling the pedal, I plugged it up. Within a few seconds I heard a pop and saw the magic smoke escape from the new capacitor.
- My next assumption was that the power supply’s transformer might be faulty and was sending too much voltage to the capacitors. But, after measuring with a multimeter, the cap was getting 24V dc–not enough to fizzle a 35v cap within seconds.
- A search for anything that could be shorting the capacitor came up negative.
- After staring at the blown capacitor for a while, I noticed something so obvious that I was sure it couldn’t be the solution. If you look at the other 470uf capacitor, the one that isn’t blowing, it is mounted with the negative stripe in the same direction as the 100uf capacitor next to it. The negative stripe on the problem 470uf capacitor is mounted in the opposite direction of the 100uf capacitor next to it. see Exhibit D.
- When I looked at the pinouts labeled on the bridge rectifier, the (-) was going to the negative on the good capacitor, but the (+) was going to the negative on the on the blown capacitor. see Exhibit D
- I got another capacitor and mounted it so the the (+) of the bridge rectifier was now going to the (+) of the capacitor.
- After testing, there were no pops, smoke, hums or buzzes. The pedal was once again fully functional and operating properly. see Exhibits E and F
- The pedal worked fine under steady use for three years and was 100% functioning immediately prior to selling.
- Within a week of the new owner receiving the pedal, it was deemed broken and sent back to me for a full refund due to it falling within the stipulations stated in my return policy.
- I found a blown capacitor that when replaced with a new one installed in the same direction as the original blew again within seconds.
- The capacitor in question was found to be installed backwards. Installing a new capacitor in the correct direction solved the problem.
OK, those are the facts. WTF happened?