Members Unalaska Posted July 14, 2015 Members Share Posted July 14, 2015 I've got a sick EV T52 here and it's the crossover. I've swapped out HF drivers, and now I've got the crossover itself apart and checking for bad resistors. There are 3: R1=2.7ohms, R2=20ohms, R3=10ohms problem is my multimeter says R1=0.3 R2=1.6 R3=1.5 so unless the values just changed out on these out of nowhere I'm not sure what to make of this. The cap is a single 1.5uF 100v and a place where an 18uF should be but there's no sign of it ever being there (not hot glue, no sign of soldering there) attached are some pics Link to comment Share on other sites More sharing options...
Members Unalaska Posted July 14, 2015 Author Members Share Posted July 14, 2015 Here's a pic of the backside Link to comment Share on other sites More sharing options...
Members Unalaska Posted July 14, 2015 Author Members Share Posted July 14, 2015 I opened up the other cab/crossover and the resistor values are identical. The "missing cap" too, looks like the PCB is used for more models than this one (very common) so I'm at square one. Link to comment Share on other sites More sharing options...
Members wesg Posted July 14, 2015 Members Share Posted July 14, 2015 Aside from being sick, what is the crossover doing/not doing? Caveat: I am not an electronics technician! If you are measuring the resistance of the 2.7 ohm resistornote that it will read low in-circuit as it wired in parallel with a (10 ohm resistor + 1.0 mH inductor)... I would expect it to read around 2.3 ohms. 0.3 ohms seems suspiciously low, though. Is there a path between W+ and T+? (Is the crossover disconnected?) Now, I don't see a 20 ohm resistor on the schematic. But one of the 10 ohm resistors is in parallel with a (2.7 ohm resistor + 1.0mH inductor) and the other is in parallel with a PTC thermistor. The first one, in circuit, I would again expect to read around 2.3 ohms assuming the crossover is out of the speaker and I'm looking at the right schematic. The second one, the reading will change depending on the temperature. The good news is that most of these parts tend to -- in my limited experience -- fail with visual clues. Depending on what's wrong, I would be looking at the jacks, the capacitor, and a thermistor -- provided I had continuity across the inductors and and no obvious damage to the sandbar resistors. It's weird that I can't see the thermistor in the photos. Maybe my schematic doesn't describe your revision. http://elektrotanya.com/electro-voice_t52_sm.pdf/download.html Wes Link to comment Share on other sites More sharing options...
Members dboomer Posted July 14, 2015 Members Share Posted July 14, 2015 What does a "sick" speaker mean and why do you suspect the crossover? Link to comment Share on other sites More sharing options...
Members Unalaska Posted July 14, 2015 Author Members Share Posted July 14, 2015 Sick just means I'm getting the 15 just fine but very reduced (not eliminated) HF output. I can hear the horn quietly with the battery test 1.5v but it isn't near as loud as the other matching cab. there is a poly switch rated 0.5a 70v which dampens the HF when the HF driver sees too much power. That may have failed so I bought that and will replace when it arrives. Link to comment Share on other sites More sharing options...
Members trevcda Posted July 14, 2015 Members Share Posted July 14, 2015 I would get a set of alligator clips and bypass the poly switch under very controlled conditions. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted July 15, 2015 Members Share Posted July 15, 2015 First off why are you not removing one side of the component off the PCB to and then measure?Also, really suspect the compression diaphragm for issues.More so then the xover theory, Link to comment Share on other sites More sharing options...
Members agedhorse Posted July 16, 2015 Members Share Posted July 16, 2015 If you have swapped HF drivers and the symptom stayed with the original speaker then the crossover is likely. A common problem is an open series cap on the high pass filter to the horn. You need to remove the cap at one end and use a capacitance meter to verify values. I think you will find one essentially open or changed to a much smaller value. Link to comment Share on other sites More sharing options...
Members Unalaska Posted July 16, 2015 Author Members Share Posted July 16, 2015 I've never seen a capacitance meter in the wild, I'll have to look that up. Ill order the replacement cap too, it's east to replace Link to comment Share on other sites More sharing options...
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