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Old 7th January 2012, 02:37 AM   #1
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Default Xtant 3300c No Output

I have here 2 xtant 3300c's. Both powers up on my bench via 12volt supply. Red power indicator lights up on both. All external add-on cards removed and jumped for bypass. Noise Gate off. No audio output from either amp. There is DC offset of 3volts accross all speaker outputs for one amp and about 2 volts DC on the other amp. I read somewhere in these forums to check the J108 (driver transistors?) and one amp show ~8.xx volts on pin 1 on all three J108. The other amp shows ~12.xx volts on pin 1 of all three J108. I have access to a scope if you need readings but you will have to guide me as I am a newb when it comes to the scope.
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Old 8th January 2012, 12:10 AM   #2
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Pins 1 and 2 should be near 0v. Pin 3 should be at or below -10v.
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Old 10th January 2012, 04:01 AM   #3
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Sorry for the delay. Babin, you are correct. On J108, pins 1 and 2 are 0v. Pin 3 is at 11.68v on all 3 J108s. I believe the other amp pin 3 has about 10v on all 3 J108s. For now I will just focus on one amp so as not to confuse. I get +44.6v and -42.7v for the rails. The emitter resistors for these are all at 3.26v. I also get +26.38v as well as -24.89v. The emitter resistors for these. 6 are at 3.083v. The other 6 are at 3.094v. Where should I check next.
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Old 10th January 2012, 04:09 AM   #4
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Negative or positive voltage on leg 3 of the J108 transistors?
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Old 10th January 2012, 04:12 AM   #5
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Negative voltage
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Old 10th January 2012, 04:35 AM   #6
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Just wondering if there are any tips for removing the smd resistors. I tested a few that seemed to be off but when I removed them and checked again, they were ok. Did damage a few pads that they were sitting on so had to jump them. Some of them looked darker than the rest but also checked out fine. What am I looking for as far as identifying damaged smd resistors besides the obvious. Thanks.
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Old 10th January 2012, 04:48 AM   #7
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A strong lighted magnifying glass will often show you which SMD resistors are damaged but in your amp, you have multiple identical channels so you can compare the resistors in one channel to the corresponding resistors in the other channels.

To remove the resistors, apply additional solder to both ends. Heat one end for 2-3 seconds then quickly move the iron to the other end and slide to resistor off of the pads.
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