Dieter Stoll
From:
Germany
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Posted 29 Apr 2017 10:51 am |
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So all of a sudden, the Vari-Z stopped working. No effect at all when turning the pot. The pot has taken a hit and cracked, Brad said. Turns out he was right. Maybe better to mount the pot differently so that if and when it takes another hit it won't break on the inside. Read the story below.
This is how the pot is mounted on the PCB (printed circuit board).
Front view, with front panel removed:
Once I had unsoldered the pot I checked the resistance: infinite either way (measured between the center lug and left or right lug). Which means that the crack must have been complete. I pried the pot open (by bending the four tongues visible in the previous pic out of the way), but failed to see a crack.
It was only under the microscope that the crack revealed itself to me:
OK, next step, get a 1 megohm audio (logarithmic) taper pot with the correct dimensions. Thanks to Brad's help I was able to locate the right pot (even here in Germany) for next-day delivery. Following Brad's advice I now mounted the pot only to the front panel, with no rigid attachment to the PCB, see below. Everything is back to normal now. Thanks again for your quick and precise advice, Brad!
Yes, there are only two wires leading from the PCB to the pot. This is because it does not work as a voltage divider here (in which case we would have needed all three connections) but as a variable resistance. |
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