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Old 28th October 2011, 04:14 PM   #1
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Default xtr 275 amp repair

this is my first post. I have a Xtr 275 revision C that is in need of repair. It has a blown fen16c rectifier and some issues with a resistor off the back of the power supply caps. I have a photo that shows the resistor i speak of. Thanks for the help. Would love to work through a full repair and add to my collection. HCCA 250, xtr2150, mbr70, xtr 275? If this is not the right section let me know...Click the image to open in full size.

thanks for the response Perry.
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Old 28th October 2011, 04:53 PM   #2
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ps thank you for the photo that i picked up off this blog also.
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Old 28th October 2011, 05:03 PM   #3
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The problem would seem to indicate that there is a leaking or shorted transistor. Have you checked all of the transistors in that channel carefully?
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Old 28th October 2011, 05:15 PM   #4
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which transistors should i focus on? 6488's or the 6491's i believe..will i need to check it on or off the board?
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Old 28th October 2011, 07:11 PM   #5
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All transistors in that channel. Shorted transistors can be found in-circuit. If you suspect that one is leaking, you may have to remove it for definitive results.
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Old 29th October 2011, 09:12 PM   #6
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if the fep16ct and fen16ct chips are removed off of the board the resistor does not burn up, however the torroid makes a very high pitched hiss. What job do these to transistors do? Thanks
Also I have replaced the stock 3300mf 35 v caps with 4700mf 50v's out of a rockford. I noticed that only one of the two terminals on both caps have 12 volts. How is this possible.
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Old 29th October 2011, 10:10 PM   #7
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delete post regarding caps. I must not be feeling to well today. Wow.
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Old 30th October 2011, 09:05 AM   #8
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The FEN/FEP components are the rectifiers. Without those, you won't have rail voltage.

Did you check the transistors?
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Old 30th October 2011, 03:23 PM   #9
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Amps torn down on the work bench at the shop. doubt ill have time to get back to it till Monday. And yes Perry, i have checked all the fets. Perhaps my technique is wrong. they all show some form of resistance to ground. however when i get them off the amp(ive only down one channel) they check out. I have read the bcae1.com write up for checking leaky/ shorted fets.
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Old 30th October 2011, 05:29 PM   #10
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You don't check transistors to ground. You check them between the legs of each individual transistor. You can't check for leakage in the circuit (unless it's leaking badly). In-circuit testing is typically only useful to find shorted transistors.

Pull the MPSA06/56 drivers and check them out of the circuit. Don't pull the outputs yet.

Did the amp draw excessive current when it was burning the resistor?
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