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Crown XTI4000 no power problem


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#16 piter2

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Posted 21 March 2014 - 02:20 AM

Great success Alain ! Amplifier works. That is, it turns on and stays on. I will check it tomorrow with signal source and speakers.
What basically happened, I thought I only had bad IGBT's and FAN device . After replacing IGBT's and FAN7380, the amplifier still would not power up.
The key to fix it, was to replace IGBT's , FAN7380 and TL494 all together. Now with all those new components it finally turns on.
Hopefully this thread can help someone out with similar problem
I will update it when I fully test the amplifier within couple of days.

#17 joust

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Posted 24 March 2014 - 09:15 AM

Glad to have been of service! :)

Alain

#18 piter2

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Posted 24 March 2014 - 09:20 PM

I wanted to confirm the amplifier works and sounds great. Bias is steady and it keeps playing without any problem.
Thank again Alain.
Having said that, I encountered another problem :)
I put both of the amps together after testing the one I was working on and realized over the weekend, the working unit developed a problem.
It works but has audible sound even with no input. It is kind of like motor boating sound. When connecting input source it is still there but with more volume it is barely hearable. This is the unit I used parts from to test the other amp but it now has all new IGBT’s, U14 and U18 IC’s .
I checked it to see if I might have overlooked something but everything seems OK. I will try to trace this odd sound but I am suspecting either one of the power supply caps or one of the op-amps perhaps. I am noticing service manual supplement has similar problem listed and recommends replacing couple of resistors. I will try that first.
Have you ever encountered similar issue ?

#19 joust

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Posted 26 March 2014 - 03:08 PM

Hey this is a first for me too! No, I haven't had this symptom before. If you disconnect the display board, is this noise still audible? If not, then it may come from the input circuitry. I have seen cracked 82 ohms resistor between chassis and ground on the input connector circuit location (note : this 82 ohms is available on newer main boards). Though, I don't know if this has the same symptom.
Is this noise audible in both channels? If so, then I would check the regulators or another common source. Try swapping display boards...
Can the noise be modulated by the level controls? How about the DSP? Is it possible that a preset may have too much gain or something? Try with DSP OFF preset.

Alain

#20 piter2

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Posted 26 March 2014 - 04:33 PM

I performed three recommended updates ( 3 new resistors, capacitor in DSP circuit and discharge resistor ) . I swapped ( tried it with display board removed too ) the display boards as well. Motorboating tone is still there. It is kind of erratic and it goes away after 10-15min of music playing then comes back after turning the amplifier off and back on. I think I will let it play for extened period of time and see if the problem is still there. It sounds like a capacitor or weak soldering joint.
The sound is in both channels and its independent from volume control. As the music is playing its frequency changes a bit - seems like the tone frequency slows down. Besides that, music playing sounds great without any distoritions or drop-outs whatsover.
I tried changing settings ( DSP off, different presets etc ) and it didnt do anything.
I will check the 82 ohm resistor you mentioned.

Peter

#21 joust

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Posted 28 March 2014 - 09:50 AM

Verify the filter caps of both the SMPS HV and the secondary HV circuits. I have seen bad secondary filter caps. Do you perceive that the caps are domed? Press your thumb delicately on the tops of the caps : The [metal] tops should be flat. If you 'feel' a curvy top surface (underneath the plastic top cover), I would replace all four caps. You can 'remove' the top plastic cover on top of the cap; You will have a better view of the 'dome'. Though, it might be difficult to replace the plastic top once it's been removed. You could use electrical tape to secure/isolate the top of the cap.

If you have a capacitor checker, it would be a good time to use it!

Hope this helps!

A.

#22 piter2

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Posted 09 April 2014 - 05:40 PM

Alain. Life kept me busy for past 10 days or so but I finally got a chance to take the amp apart again and check the capacitors.
I checked radial capacitors with my ESR-Micro V4 tester and they all check out OK. ESR is low, capacitance varies ( due to testing in circuit I suppose ).
I did check tops of main filtering caps and they seem flat.
I am going to take the other , working amplifier apart and check/compare tests results of the caps.
If test results are close to each other, I will try to trace that tone or possibly replace couple of op-amps. I ordered 4 of them last time.
In the worst case I will still have working amplifier with motorboat tone that goes away after 15 minutes :)

#23 joust

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Posted 10 April 2014 - 08:56 AM

Did you notice if the noise eventually disappeared with the cover removed? If so, then it could be thermally sensitive.
Since the 'noise' disappears after a while, why not try some freeze spray on the components when the noise is observed?
If the noise should disappear, use a heat gun to reactivate the noise.
Verify the 3.3V circuit : It is derived from the 5V regulated supply.
I don't think it comes from the SMPS but from the secondary side.

Follow the signal :
Inject a 1KHz signal into one or both inputs.
Verify and scope the output waveform and determine if you can 'see' the motorboating signal with sine wave.
Verify then the input to the A/D converter and the output of the D/A converter.
If the noise is visible, try to use the EQ of the DSP and observe if it has some behavior on the noise.

Note : It is possible to have a bad A/D converter.

A.

#24 piter2

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Posted 11 April 2014 - 03:45 PM

I dont think covers being removed helps the problem. Initially when I finished the other XTi4000, I put them both together.
When I realized this one has audible tone I took it apart to check for anything I might have overlooked when I replaced those parts I used to test the other amp. After I did not find anything suspicious, I had it running with covers off with the same results.
I did notice that when I turn the amp on and have music playing louder ( more heat generated ) , the tone goes away sooner than when the amp is just idling or has music playing at low level.
I suspected weak/cold soldering joints and re-did many of them but there still maybe some as this is multilayer pcb.
I sent my scope for re-calibrating and will have it back on Monday or Tuesday and I will try to trace the tone.
I will check A/D converter specifically.
When I use EQ , the tone goes away for a split second but I guess it the result of muting the signal when changing DSP settings.