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About CurtZHP

  1. D-75 Amp -- Suspected fault in IOC

    Found the problem, after I replaced D1. Was still seeing excessive voltage on that rail. Upon closer inspection with a magnifying glass, there was a hairline separation in the trace between R2 and D2. So the diode was effectively out of the circuit. Used a thin piece of wire to reinforce that trace, and all's well!
  2. D-75 Amp -- Suspected fault in IOC

    OK. Was able to at least check voltages. +/- 30 rails are healthy. Measured +/- 10V rails at the IC's. +10 is good, but -10 rail is reading around -25V! D1 bad??
  3. D-75 Amp -- Suspected fault in IOC

    Finally got this thing on the bench! (Busy...busy...busy....) I have the schematic, but I'm having a little trouble locating where the supply voltage gets regulated down to +/- 10VDC. I can see the +/- 30VDC off the main supply. Also, my pdf of the service manual doesn't have a very clear image of the main pcb. Any idea where I can find one?
  4. D-75 Amp -- Suspected fault in IOC

    I'll give that a shot. Thanks!
  5. I haven't opened it up yet, but I figured I'd post here before diving in. I have an original Crown D-75 amp, connected between a Tascam DM-24 mixer and a pair of Event 20/20 passive speakers. Same setup I've been using for years. Up until recently, the amp lived in a closet just outside the studio, in a rack with the noisy computer. It has since been moved into the studio to join the rest of the outboard gear. Still connected to the same gear, and powered from the same exact branch circuit. I've noticed that the IOC indicators light up quite frequently. I have each channel's level control set to about the 1 o'clock position, and I tend to monitor at reasonable levels (rarely louder than 90dB, measured at the mix position). It's not just when using the Tascam mixer. I've also tried connecting right from the balanced outputs of the sound card, with and without a passive attenuator between them. Usually, the IOC lights will sort of flicker with the music, acting almost like peak indicators. But, I also notice that once there's sufficient level to make them stay on, they stay on long after the music stops. Incidentally, the music sounds clean even when the IOC's are lit. I'm not hearing any distortion. I haven't tried just running pure tones yet. Thoughts? P.S.: Several years ago, I did have to perform the typical cooked resistor replacement, along with the attendant diode. (Don't recall the exact part designations...)
  6. I've got a GLM-100 here that seems to be broken. When plugged in all I ever hear out of it is handling noise. Speaking into the microphone only produces audio if I practically put the thing IN my mouth! But handling the wire or the mic itself produces all manner of sound (none of it useful). It also seems to have a very high noise floor (hiss). Is the capsule shot? I'd also like to confirm that the capsule is wired properly to the "plug" portion of the mic. Looking at the PCB, there are three wires from the capsule - red, white and ground. What is their correct orientation? The schematic in the included literature doesn't say. I basically found this thing in a drawer in the transmitter building at the station where I work. It was going to get tossed. I'm beginning to see why.
  7. D-75 Calibration questions

    I'm assuming the CMR pot is the one located on the non-inverting input to U2 on the schematic. (CMR=Common Mode Rejection?) And just to verify, R101 and R201 refer to the front panel level controls? Also, once I clean the CMR pots, how do I verify their correct settings? Thanks.
  8. I've got an older model D-75 that has served me well. I've already replaced the 820Ohm resistors with 910's, so that's taken care of. The new problem I've discovered is that the right channel does not put out as much level as the left when the level controls are set the same. Is there a way to calibrate this unit to get them to match, or am I looking at a larger problem? I checked the service manual and didn't see anything about it.
  9. NEEDED: D-75 Schematics

    E-mail sent. Thanks!
  10. Anyone got a pdf handy of the schematics for the D-75? I'm talking about the old style unit with the gray face plate and round silver knobs. Serial number 031186 (if that helps). It's got the "rice crispies" in the left channel again. Last year, I replaced the notorious 820 Ohm resistors with 910's, but I've read that there are other things that might need replacing as well. I'd like to have a road map before I go any further.