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About Lou

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  1. I agree with Kevywevywho. Get a VOM and check for DC on the speaker terminals without a speaker connected. It should read zero or very very low.
  2. I'd say your diagnosis is correct.
  3. If you are ever unsure of what your level is, most ANALOG multimeters have a db scale when the meter is set to 3 Volts AC.
  4. You know, I'd like to see Crown adopt the same fan philosophy that another amp mfgr (starts with a Q and ends with a C) has adopted. And that is, the fan always spins (but slowly) at turn on when the amp is cold. This is what I call "fan confidence". If you don't see the fan spin at turn on , then you have a problem!
  5. This is what I think. A small piece of conductive material- might even be solder flashing-got across the HV and vaporized. If you cannot see anything on top burnt, then it may have occured on the bottom of the board. If your unit is not in protect now, you're lucky. I would open it up, shake it real good, and then blow it out with an air hose. There is the possibility that some of the debris is still floating around in there.
  6. The loud pop you hear is DC hitting the speaker (not good). You should not see the woofers going in and out as the volume controls are rocked. Sounds like you have DC leaving the front end (preamp section). Does it do it on both channels? Is the amp vibration sensitive? Does it make noises when you tap on the cover? You might have a loose connection on the circuit board particularly around the output transistors.
  7. There are some smt resistors in the emitter circuits 0f Q1,2,3 (those square darlington transistors) that feed voltage out to the fan connector. I've seen them go open and cause this effect. They are very small, .22 ohms I believe.
  8. While you're in there, don't forget the Crown first rule of thumbs: Never touch more than one heatsink at one time!
  9. Is the defective side running "hot" to the touch? Can you measure any DC voltage on the defective side's output terminals? Check your speakers and wiring with an ohmmeter and verify there are no shorts. Some versions of amps might have components missing from the circuit board.
  10. That's really pretty. I hope it doesn't overheat when its all fired up!
  11. I have never seen a blown op amp in one of these. Also check your ribbon cable connections to the main board- a problem if the ty-raps have dried out and broken. And when you're finished, you might want to check the bias setting for both channels. You'll have to partially remove the main board to get to the emitter resistors for the other channel. If you didn't have any blown outputs you truly are "Lucky."
  12. Don't reconnect your speakers until your DC output problem is resolved. If your emitter resistors on the outputs are not burned up, then the outputs are probably OK. If you had a defective 7815 and you still have problems on a channel, I'd look at the voltage translator stages DC busses. They should be +0.6 and -0.6 Volts DC and they should be equal. If one side is higher or lower then you probably have a fault. Also check your ODEP voltages. They should be about + and - 10.5 to 11 volts and will probably not be equal. I've seen those UPA75/76 transistor SIPS go out and give trouble. And don't forget about the green 100 ohm resistors in the ODEP circuit that go off value.
  13. This must be an older PB. The new ones have DC protection which shuts it down to prevent DC on the output. Check for burned up components on the output board and the main board. You can get the schematic free off this here website. Good luck.
  14. Sorry no one has gotten back to you on this. I have a CT400 and have never seen this problem but then I did do a capacitor job a couple of years ago. At the age of this amp, I think your problem is a defective cap in the feedback loop of U104B. It is C144 and is a 100uf at 35V located on the main board. You should probably change C244 while you're in there. And you should check the four 100 ohm resistors in the ODEP circuit (on each channel) on all your amps. Tech bulletin 95 addresses this. Ask David Glass to send it to you.
  15. Hmm, I thought the JRX was the replacement for the Mpro. Before you do anything with the MPro amp, CHECK THAT SPEAKER!!! Most often when the amp blows, the speaker is bad too. First, remove the grill and verify that the cone moves freely in-and-out without any scraping sound. Second, stick your nose in the center and sniff if it smells like a burned TV dinner. Third, pull the speaker and check the resistance with an ohmmeter. It might be shorted (which would blow your amp) or it could be open. Those are 4 ohm speakers but it might be 8 if it has been replaced before. Take the speaker to a sound shop and have it checked. The good news about your blown amp is that its like a Crown CE. Most likely only one side is blown making it easier to troubleshoot. And there are a lot of CEs out there and a lot of amp techs have a lot of experience with them. Incidentally the JRX (and maybe the prx) is a switching amp. And thats a whole nother can of worms. Good luck.