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XTi4000 Not Working

Xti4000 not working dead power supply

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#1 starlight9088

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Posted 05 August 2013 - 04:31 PM

Hi There.

I have a XTi4000 that will not switch on.  I purchased it on 31/05/2010 from an Ebay company which has since ceased trading.  Upon contacting Sound Tech (just within the warranty period) they told me they suspect it is a grey import and would not fix it for free.  How can I tell if it is from the US or UK?

ser: 8500332406
part: NXTI4000
build: 11/29/2009

Can anyone help me here? I need to get it fixed (I'm in Somerset, UK)

The Amp doesn't respond to being switched on, no leds light, etc.  The internal fuse is ok.
I tested the output of the rectifier that is putting out 300v DC... Is this normal?


Please help!

Thanks in advance.

Andrew

#2 joust

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Posted 06 August 2013 - 07:10 AM

Hello Andrew, by any chance this XTI has some (6) 'fat' bluish resistors in the SMPS section?

A.

#3 starlight9088

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Posted 06 August 2013 - 07:30 AM

Hi there.  Thanks for your reply.  There are a group of 6 resistors near the on/off switch, referred to as R370-R374 and R378 which are 48.7K 1%.  Should I be suspicious of these?

#4 joust

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Posted 06 August 2013 - 12:01 PM

Yes! And there are two others hidden amidst the filter caps (total 8). Furthermore, locate two of the same type of resistors (37.5K) near the output coils: these two would also need to be replaced, if they're the bluish version!

A.

#5 starlight9088

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Posted 06 August 2013 - 12:18 PM

Thank you so much for your advice.  

Are these the resistors that were/are part of the recall? Do you think this will fix the issue or could it have wiped out something else on the board?

I will go ahead and replace these ten resistors.  Thanks again, I will post the result of my progress!.

#6 starlight9088

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Posted 08 August 2013 - 10:46 AM

So I've de-soldered all ten of the resistors and eight of them are testing incorrect values (by quite some way).  I'm now finding it quite a challenge to find a source to buy the correct replacement resistors.
If anyone can help me, I need

8x  47.8KΩ, 1 Watt, 1% resistors
2x  35.7KΩ, 1 Watt, 1% resistors

Thanks in advance


#7 starlight9088

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Posted 19 August 2013 - 11:16 AM

I have replaced the resistors with new ones from Crown but the amp still does not work...   Does anyone out the have any other ideas as to what the problem could be?

#8 starlight9088

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Posted 19 August 2013 - 11:18 AM

(by the way.. the resistors were faulty, the value readings of nearly all of the resistors were out by quite a lot)

#9 joust

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Posted 19 August 2013 - 12:14 PM

There are a few reasons why an XTI will not power up nomally:
- Check 20A AC fuse; Make sure when cycled on, that 170V is available at the BULK voltage TP;
- If the SMPS has not fired, make sure that there is no shorted output or Tracker module devices; Verify that the chopper drivers are OK;
- Verify all the small SMT caps in the SMPS: I have found shorted C201, C186, for example.
- Verify the kickstart cap C196;
Alain

#10 starlight9088

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Posted 05 September 2013 - 08:43 AM

Hi Alain.  When testing the BULK voltage between TP30 and TP21 I am getting 335vdc, not 170vdc.  Is this suggestive of anything in particular to look at next?

Thanks.

#11 joust

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Posted 05 September 2013 - 09:14 AM

You're in Great Britain? Then it may be possible that the 335V is derived from the 220V operation. Here in North America, where 120V is accessible, the BULK voltage is half that, and once the SMPS is started, a doubler circuit brings it to normal (340V) operation.
Though, I am quite surprised that the resistor replacement has not worked out.
NOTE: Reference in the SMPS is not chassis GROUND! Locate and use TP21 as your 0V [V_BULKRTN] reference.
Are the eight resistors are properly located in the SMPS section and the two other resistors in the output coil section?
Can you verify the signal at R375 in the SMPS section? (Normally, a 16V DC signal should be present.)
At the zener and R375 junction describe the signal there: Is it steady (around 1.5V)? Does it flucuate like a cap charging and discharging?

Alain

#12 starlight9088

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Posted 05 September 2013 - 11:02 AM

The resistors are in and ive checked them against the circuit diagram, etc.  

The voltage reading i get between the R375 junction and TP21 is steady at 6.3vdc?!?!

#13 joust

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Posted 05 September 2013 - 11:46 AM

In an earlier post in this thread, I mentionned to verify kickstart cap C196. It's the electrolytic near the six resistors in the SMPS circuit. I'm pretty sure that it may be defective.
Note: If the cap was good, you would see a low voltage (perhaps 4 to 8V) pulsing signal at the R375 junction. Replace the cap with a 100uF/25V; I would try a 35V if available and I recommend the 105°C version (because of the heat generated by the resistors, though less problematic than the eight resistors in line of a previous version of the XTI!).

Alain

#14 starlight9088

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Posted 05 September 2013 - 12:40 PM

Great, I will try that.  Do you mean 220uF? that is what C196 is labelled as.

#15 joust

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Posted 06 September 2013 - 01:12 PM

My bad, yes a 220uF. Ikes!





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