Kicker ZR1000 - hissing from coil area of pcb - diyAudio
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Old 12th May 2012, 05:47 PM   #1
diyAudio Member
Join Date: May 2010
Default Kicker ZR1000 - hissing from coil area of pcb

Hi, new here, I very much appreciate all of the advice, insight and contributions made by everyone here - Thank You Very Much!!!

I'm working on a ZR1000 which came in not playing and emitting a hissing sound in the vicinity of the transformer and filter caps. The transistors checked okayhowever meter revealed only few volts from the diodes after the transformer secondary. BOTH voltages were positive!
I have a 60 watt bulb in series with my supply and a 2 ohm resistor in the 12v line to the amp. Usually when I switch on the power to an amp my lightbulb glows dimly while the caps fill up then goes dark (depending on load and shorts) - however in this case the bulb gets brighter and stays on indicating high current draw.
So I took it out and looked it over. I found several bad solder joints on the back side, some so bad the component's leads were completely disconnected and could be pulled out of the top of the board. I reworked the backside of the board. Then I tested it (PC power supply 12v) and found + and -26 volts or so at the power supply output diodes. I applied audio, and it played well. But, it was still hissing from somewhere near the powersupply transformer. So I bolted it to its heatsinks to continue testing and tried it - now it doesnt work... No voltage out of the diodes.
So, I reworked the part of the front side of the board around the switching controllers, and the hiss changed from a windy white noise hissing sound to a high pitched whine in which you could hear the switching sound (on and off).
So, I'll probably ohm the resistors, esr the caps, and rework the rest of the board....

What next folks?

P.S. I have the schematic...
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Old 12th May 2012, 06:32 PM   #2
diyAudio Member
Join Date: May 2011
Could it just be toroid noise you are hearing? I am still learning but I notice on larger amps the toroids can get noisy when you listen close.

Another thing (not trying to teach you to suck eggs by the way)
Clamp down heatsink's before you ever put power to an amp, the fets burn faster than you can react. I learnt the hard way
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Old 13th May 2012, 05:00 AM   #3
diyAudio Member
Join Date: May 2010
Doh! from the post at the link below - "secondary winding is isolated from the power input ground" - yep, ok, I have + and - supply ok. Amp plays ok atm.
Kicker ZR1000 issue

Toroid noise? Well, I would think it is, except that its so loud. I can hear it switch, and the frequency starts around maybe 1000 hertz and rapidly speeds up to around 16kilohertz or so.
I reworked more of the top, and now the switching frequency is higher and more stable, but its still drawing a heavy load at idle. I measured about 7.5volts after my inline V+ resistor - so is it possible that its sucking so much current because the supply voltage is too low? Perhaps its trying to push the rails up to a certain voltage - others have mentioned +55, I'm getting about +-26 at the diodes - should I be getting +55 and - 55?

once again I really need a scope - coulda checked wave to the drivers...
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Old 13th May 2012, 05:42 AM   #4
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Join Date: Nov 2003
Location: Louisiana
You need to remove all current limiting, insert a 15 amp fuse in the B+ line, clamp all transistors and then check the current draw and rail voltage.
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Old 13th May 2012, 06:05 PM   #5
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Join Date: May 2010
I removed the limiting and the power supply cuts off during the initial surge. That's part of why I use the limiting; because my supply can't provide enough reserve for the initial surge.

I observed something interesting - I set it up with a 5 ohm current limiting resistor in the 12v B+ line - then I turned it on, and paralleled that resistor with another 5, and the pitch of the whine changed higher. So my question - is the change in pitch of the whine caused by the switching frequency changing or the pwm duty cycle? From the datasheet of the SG3525 it oscillates from 100hz to 400khz. I thought the point of Pulse Width Modulation was to pick a frequency and stick with it, just varying the on-time duty cycle...
Any thoughts?

Also, I searched for a minute, but is there a good site/thread anyone would recommend for modifying a pc psu into a bench supply? I know I can tweak the voltage by changing the resistors around the opto-isolator - I know theres a better way? Also, Any thoughts on forcing the supply to stay on when the load/current changes quickly (such as turn on surge)?

Thanks again folks!
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Old 14th May 2012, 02:41 AM   #6
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
The frequency is determined by the timing components. It should not vary. You could check it with a frequency counter or a scope.

After it starts, bypass the 5 ohm resistor.

If you're going to do this type of work, you should buy a more suitable power supply with meters for voltage and amperage, as well as an adjustment for the voltage. I prefer Astron supplies but if you don't want to spend that much money the PS-52KX works well enough.
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