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XTI 4000 Not powering on


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#1 Fspatola

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Posted 24 October 2013 - 07:28 AM

Hi, this is my first post on this forum so please bare with me. I have been working on my xti4000 that will not power on. It is totally dead no lights nothing.
It seems like the problem is in the smps. I believe on TP28 I should have 15 volts I have 0. On tp30 I have about 180 volts. On R375 I have 0 volts on the Zener Diode Side it should be 16V. I replace C196, C201 & C186. Still nothing. Any ideas would be greatly appreciated. Thank You, Frank

#2 joust

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Posted 24 October 2013 - 09:07 AM

Welcome Frank!
I see that you've been reading my posts! :)

First thing first: Verify the load resitors (47.8K) for the zener diodes: If they're blue, fat and very colorful, then contact your local authorized Crown service center and ask for the TN205 solution.
Of course, also verify smps chopper devices, output devices, drivers, and the fets on the tracker module: If a short or defect is present, the amp will not start.

If the load resistors are greenish and slim, then read on:
I believe you are on the right track: You did verify the R375 voltages. OK, so you measured 0V. Here is what I suggest:
Remove R375; Scope or check the voltage on the zener, with reference to the bulk return reference (TP21. Note: this is not a chassis ground. BEWARE!)
With the resistor removed, four different signals should show on D8:
0V  : the load resistor is open : check above; If resistors and D8 are fine, then you may have an issue with IC16, the Fault circuit or the crowbar circuit;
16V: the load resistors are fine, downstream you may have a shorted bypass cap or modulator is disabled (possible short in amp detected);
2V  : if steady, then the kickstart cap (C196) is open (apparently, not this case!);
2V  : if charging and discharging : kickstart cap is functionning; check the bypass caps (such as C201, C196, etc);

Hope this helps!

Alain

#3 Fspatola

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Posted 24 October 2013 - 09:51 AM

Hi Alain, Thank you for the super fast response.
Yes I have been reading your posts they are awsome. I was hoping you would respond to my post. I got lucky...I guess.  The load resistors are the green ones and all test good. I suspected that ic16 is shorted because there is no voltage on pin1. Is there a test procedure for ic16. I will remove R375 and check for 16v on the zener side anyway. Also I will check D8 as you suggested.
I will let you know my findings. Thank You again.

#4 joust

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Posted 24 October 2013 - 10:12 AM

No, I don't think the that U16 is problematic (very rare!). Normally, the outputs of U16 should read high impedance, hence the 16V at R375 (when normal!). R375 has to be removed to verify if U16 is correct or not, or that the Fault detection has not been enable (< 0V or low impedance). Also, don't forget that BOTH pins 1 and 7 of U16 are tied together!
Correction : I meant D31 (the diode tied to R375) not D8! Sorry.

Alain

#5 Fspatola

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Posted 24 October 2013 - 11:31 AM

Oh ok D31 I did check that one.

#6 Fspatola

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Posted 25 October 2013 - 07:26 AM

Ok, sometimes I get so fixated on one thing (SMPS) that I overlook the obvious. (Shorted FET in the tracker circuit).
Thank You Alain.