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CTS1200 Static both channels


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#1 xtrememachines

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Posted 19 March 2014 - 08:34 AM

CTS1200 just started emitting static from both channels with and without audio playing. I switched speakers to another CTS1200 and they work fine. Any ideas on what would cause the static?

#2 joust

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Posted 19 March 2014 - 08:59 AM

Hello,

Test : You must have only the [8 ohms] speakers connected; Level controls minimum; Mode switch set DUAL; Internal i/p gain switch set to +4 (not distributed!), towards the reear of the unit; No input signal or connections to the amp.
If you still have static filtering through, then it may be a supply issue; Verify the +/- 15V regulators located beneath the silpad of each heatsink. I may even suspect C933 of being perhaps flaky.
If you don't have any static sound, slowly increase input levels; If static appears, you may have an input issue, probably in the LV section.

Alain

#3 xtrememachines

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Posted 19 March 2014 - 10:40 AM

I just went to test it out and when I turn it on I get no sound at all and the Ready lights are off, but the number 2 ready light and the data light on the back side are on but barley visible unless you get real close to see them.

#4 joust

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Posted 20 March 2014 - 08:05 AM

I believe you have a low voltage power issue! Reread my previous post for locations of the possible fault.
Can you do measurements? Do you have troubleshooting equipment?
If not, then I would recommend that you get in touch with your local authorized Crown service center.
You won't be capable of investigating and subsequent repair of the amp without these resources.
Do have a glorious day! It's cold, damp and raining a bit, here! :-)

Alain

#5 xtrememachines

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Posted 20 March 2014 - 11:28 AM

Can these amps be powered up with no speakers connected?
I pulled the amp out of the rack and powered it up on the bench with no load and it flashes fault and clip.

#6 joust

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Posted 21 March 2014 - 08:26 AM

Any amp, for that matter, can be powered up with no speakers. I do remember, though, in the days, you couldn't power up a 'tube' amp without a load connected. You could damage the tubes/valves when not loaded because of the back EMF of an open output transformer!

In our case, it is better to 'unload' the amp prior to investigation. Note : Power is demanded whenever a load is connected. This is the reason I don't load an amp when troubleshooting. Note : A shorted o/p device looks like a load to the amp. So, if the breaker trips, or a fuse blows when powering up, I would suspect a damaged o/p device. In the case of a CTS amplifier and usually, in the case of any SMPS equipment, this behavior (shorted output device) will be discovered by the amp's early fault detection circuitry at power up and a signal will prevent the SMPS to power up.

Now, suppose the amp powers up and appears operational (no Fault, Clip or Thermal indicators lit) then inject some signal and observe if the signal level leds modulate. If both sides were to modulate normally, then I would connect some loads to the amp. If the signal were to disappear or the amp's behavior were to change, then the loads are off and troubleshooting starts.

#7 xtrememachines

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Posted 27 March 2014 - 12:50 PM

If I leave it on smoke starts to come out of the side the power plug is on.

#8 joust

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Posted 28 March 2014 - 09:41 AM

What you are observing is the 'crowbar' circuit at work. The crowbar circuit includes an SCR device and a bank of resistors between the HV rails. As long as no Fault is detected the crowbar is not activated. When the amp detects a possible catastrophic fault in the output circuit, it activates the SCR, which shorts out the rails circuit to avoid a bigger catastrophic fault! So, if the crowbar is activated, I suspect a fault in the output circuit.
First of, remove the rails voltage from the output circuit : Locate the big ferrite beads next to the output's filter cap bank (FB909, FB910) and unsolder and remove them. Now, the rails are decoupled from the secondary power supply. Power up : Now, the crowbar should not be activated. (Confirm).
Measure the output rails [leading to the output connector] : both should read approximately 0V (referenced to ground). If you find DC, then this is the bad channel. Remove Qx12, Qx13, where x stands for the channel number. Then troubleshoot or remove transistors until the DC voltage disappears. I suspect a component in the driver circuit, perhaps the driver iteself or the HV B-C cap.

Hope this helps!

Alain