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MTX 1501D (old design) power supply issues
MTX 1501D (old design) power supply issues
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Old 27th September 2019, 05:58 PM   #11
BumpinYota is offline BumpinYota  United States
diyAudio Member
Join Date: Jul 2019
Location: Venice, FL
Well ive discovered something that also makes perfect sense but i hadnt anticipated.

But if you place ground of your oscilliscope to the amp's main ground, then place the probe on the aluminum heatsink with time divide set to 5us and voltage divide to 1v, you can see the ouptut switching wave (57kHz) being induced in the heat sink!!

You would not believe how long i spent trying to find the short to the heat sink...until i momentarily fired up the board on my rubber mat on the desk with the heat sink in my lap a good 6" away! LoL

Last edited by BumpinYota; 27th September 2019 at 06:02 PM.
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Old 27th September 2019, 06:13 PM   #12
Perry Babin is offline Perry Babin  United States
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
Heatsinks aren't always grounded. On some of these amps, there was a small capacitor (0.1uF?) between a screw and ground. You can add one if your amp doesn't have one. Paralleling a 1k resistor with the cap is a bit better because it drains off any DC as well.

This is only to shunt capacitively coupled noise to ground. If you have a bad insulator that's shorting to the heatsink, that's an entirely different issue.
Anyone who purchased the repair tutorial, email me (babin_perry@yahoo.com) if you want to download the latest version.
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