MTX Thunder 1501d Amp Repair (~2004 Model) ---Turns on (Red LED lit) but no sound - diyAudio
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Old 16th August 2011, 10:15 PM   #1
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Default MTX Thunder 1501d Amp Repair (~2004 Model) ---Turns on (Red LED lit) but no sound

I have had this amp since 2004. A few years back it shorted out when one of the power/ground leads came loose and arced. At least this is what I think happened. Since then it has not worked. It turns on but produces no sound. I have two of them, one working one not. I have used my dmm to analyze the fets and all seem to be working. And Caps seem to have little wear to none. I did however notice some oxidation on the underneath side connected to the yellow transformer and FET471 on the SouthWest side of the amp below the RCA IO's and phase switch. Here are a few pictures to become oriented with. Thank you for any help as I have little experience with amplifier repair but am eager to learn.
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File Type: jpg WP_000356.jpg (530.8 KB, 88 views)
File Type: jpg WP_000359.jpg (849.2 KB, 84 views)
File Type: jpg WP_000357.jpg (944.0 KB, 81 views)
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Old 16th August 2011, 10:37 PM   #2
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You'll need to clean the corrosion and confirm that the traces that were corroded are intact.

There are two burned resistors in the photo. They're 0.22 ohm resistors. They'll need to be replaced before you can do anything else.

This amp stores a lot of energy in the capacitors. Do NOT touch anything on the board until the LED between the large capacitors has gone completely dim/dark.

If you haven't done so, you should read the basic amp repair page (in sig line below).
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Old 17th August 2011, 12:34 AM   #3
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Okay. I just cleaned them. Everything appears to be intact with no loose connections. This amp has not been hooked up to a power source for at least a week. Will I need to discharge anything before preceding. These two components seem to appear to be where the corrosion is coming from. Only the black one highlighted is a 75339 the other says this on it....(FB42n20D ___IR 321H___5732). Also it appears that R220 SMD/SMT 's are burned up. Thank you for pointing that out. I dont know how to look those up any possibility you know what part number to look up for them? The Resistors (.22 ohm) that I have found to replace them come in a variety of wattages and % ppm. BTW thank you so much for your assistance.
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File Type: jpg WP_000360.jpg (845.2 KB, 24 views)

Last edited by thevanman316; 17th August 2011 at 12:48 AM.
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Old 17th August 2011, 12:44 AM   #4
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I understand now. We are talking about the same two 0.22 ohm resistors. Sorry Catching on. Do you know what wattage specs to replace them with or how I can figure that out?
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Old 17th August 2011, 12:50 AM   #5
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If none of the LEDs are lit, you don't need to discharge anything.

The resistors are the SMD components marked R220.

You need to measure them with a dial caliper and order replacements the same size. IF you don't have a dial caliper, I can measure the ones on a junker I have.

The corrosion likely came from an outside source. The yellow capacitors don't contain any fluid and therefore cannot leak.

The components clamped to the heatsink are FETs (HUF75339P and IRFB42N20D).
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Old 17th August 2011, 12:51 PM   #6
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I have very rudimentary tools. So if you had the measurements it would be easier as I don't have a dial caliper or a micrometer.
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Old 17th August 2011, 05:19 PM   #7
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I'll dig a board out and post the size when I get back to the shop.
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Old 18th August 2011, 11:11 PM   #8
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Digikey: PT.22YCT

The resistor was originally a 0.1% tolerance but they're hard to find. The size is 2512.
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Old 19th August 2011, 01:42 AM   #9
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I can't seem to find .1% tolerance with minimal quantity. Will 1% tolerance be okay?
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Old 19th August 2011, 02:20 AM   #10
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Yes.

Buy extras in case there is a fault that causes the resistors to fail. You may want to buy a couple of 0.22 ohm 5w in case there is such a fault. the 5w would hold up a bit longer to allow troubleshooting.
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