How do I test SDA 1.2tl before installing replacement tweeters?

zumbini

My college age son was recently gifted a pair of 1.2tl's that needed some work. I am in the process of restoring them to original condition before performing any of the many fine upgrades that are discussed on this forum. So far I have repaired rips and tears in about half of the mid woofer surrounds and replaced the grill and side panel cloth. (see http://forum.polkaudio.com/discussion/comment/2163033/#Comment_2163033)

The next phase of my project is to replace 4 non-working tweeters (T2 and T3 in both speakers) so I recently acquired 4 SL3000's in a trade with a forum member. Before I install the replacements I thought it prudent to determine if there is a problem with the crossover or wiring that took out the tweeters.

To that end I removed the dead tweeters and measured the static resistance of the circuit across the tweeter leads. T2 reads 14.0Ω (left speaker) and 14.2Ω (right speaker) which seems reasonable based on what little I understand of the circuit. Am I correct?

T3 reads 5-6 MEGAohms (left) and 7-8 MEGAohms (right) and the readings keep rising slowly over time. I know what a crossover does but I don't understand how each component affects the circuit electrically. I assume that the battery in my DMM is charging C5 and that's why the readings increase, but I'm concerned about the high resistance. Is that "normal" or does it indicate an issue with the crossover?



At that point I removed one of the crossovers and did a visual inspection. I noted a powdery white substance on some of the block resistors and some dull solder joints which I reflowed.









Then I removed or lifted one leg of each of the components are measured them:
The 22.5Ω resistor reads 23.5Ω and C5 (12mF) reads 13.4uF which seem OK

The parallel 750pF mica cap reads 0.41nF (several orders of magnitude too high)

The series 750pF mica cap reads 0.44nF (several orders of magnitude too high)

I can't get a consistent reading on the 12uF mylar cap. It either reads 0 or somewhere between .1 and 25nF (several orders of magnitude too low)

I rang out the coils (not open) but they seem too simple to fail in a low voltage application like a crossover.

If I read the schematic correctly the series mica cap and mylar cap affect all 4 tweeters. If they are "bad" why didn't T1 and T4 blow too?

Does any of this make sense?

Am I an idiot for trying to fix this myself?

NOTE 1: I used a Fluke 77 to measure the initial circuit resistances but it doesn't read capacitance so for that I used a cheap Vichy VC99. I know it reads about 5% high on resistance (versus the Fluke) but it's probably not worth the cost of recalibration.

NOTE 2: I know many of you will suggest that I upgrade the crossovers but I just don't have the money right now. I just want to install the used tweeters I picked up without frying them.

vmaxer

Good luck with this, maybe someone a lot smarter than me can chime in and help??