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AC4AQ

Member Since 01 Oct 2012
Offline Last Active May 21 2014 02:45 PM
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Topics I've Started

How to troubleshoot efficiently?

23 April 2014 - 05:30 PM

Hello to our fellow techs.

I'm wondering if there is a audio technician out there who has developed a method for rapidly locating the faulty circuit area, but not necessarily the failed components in Crown audio power amplifiers.

I've been trying to do this for two years now and am still having to create a technique for locating the trouble area when I encounter a particular Crown model for the first time. I am a technician who has had 20+ years experience in component-level work in RF power amplifiers,  servo-controlled devices and off-line converters. In the case of the servos, a failure anywhere causes symptoms everywhere, so it is necessary to 'open the loop' to troubleshoot. Inasmuch as as Crown doesn't really sell "amplifiers" such much as "speaker servos", the similarity is obvious.

However, I am now facing a K-2, with symptoms everywhere. It draws excessive line current unless both output modules are disconnected. No failed FETs, only fault found on either module was U51 (low side 12 VDC reg). Both high and low sides toggle if I feed them 12VDC, Vcc and drive the LEDs. Looking at the drive board , we have a nice sawtooth but IC 101 & 103, 201 & 203 are all locked. Going farther back, there are many pathways that can induce this failure mode.

I am not looking for the answer to this problem, but a better way to find it. The schematic tells all, too much in fact, it takes a long time to find where a bus like -LVA might go to. And there are multiple closed loops, so you can't open the loop, at least not all of them.

What  would be ideal is either a block diagram, with the test points shown so that it not necessary to waste hours looking where the fault is not. Or maybe a Truth Table for the protection circuit, to identify quickly which failure is present. Or, a flow chart.

Right now, it is the K-2. But there is an IT-6000 waiting for me next, and a smoked IT-6000 will make the K-2 look like child's play.

Thanks for any thoughts on this.

Jeff. 73 de AC4AQ

What's Z1 in a MA5002VZ?

16 April 2014 - 04:54 PM

Hello, Crown folks!

Right now I'm trying to wrap up the repair on a MacroTech 5002VZ but the last little gremlin is stubborn. It has oscillation (actually vibration) in one output channel, causing a squarish/sineish waves of about 600 mV, 300 kHz to appear at the speaker terminals.

Anyway, while applying a signal to the unloaded amplifier and as I increased the amplitude, I heard something go Pop! Nothing burned on the output module, it appears Z1 on the speaker terminal ("Terminator") board ignited.

The trouble is there is nothing identified on the schematic as Z1, nor can I find a Z1 in any of the parts lists in that enchanted forest of a service manual.

If anyone has some thoughts on this mystery component, please share them.

Thanks,

Jeff / AC4AQ