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#1 |
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diyAudio Member
Join Date: Jan 2010
Location: Gainesville, FL
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This amp had 40ohms across + and - power terminals. I bank of power supply fets was close to 0 ohms.
With no power supply fets and no power supply drivers installed I get no output from the 494. Here is what I get DCV referenced to - power terminal: 01: 0v 02: 4.89v 03: 4.74v 04: Starts at about 5v and quickly drops to 0v 05: 1.41v - has sawtooth. 06: 3.54v 07: 0v 08: 14v 09: 0v 10: 0v 11: 14v 12: 14v 13: 4.88v 14: 4.88v 15: 4.88v 16: 5.02v Pin 3 is being driven high even though pin 1 is lower than pin 2. Could this be a bad 494?
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Scope - DMM - 460W Computer PSU - Tutorial |
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#2 |
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diyAudio Member
Join Date: Sep 2009
Location: Wisconsin
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Why is 16 high, something is setting it to 5V?
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#3 |
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diyAudio Member
Join Date: Nov 2003
Location: Louisiana
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Try reducing the 12v supply voltage to about 13v.
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Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links |
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#4 |
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diyAudio Member
Join Date: Jan 2010
Location: Gainesville, FL
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Can't manually adjust my power supply so I put some 270ohm resistors in parallel and I get signal. Is this thing just that heavily regulated? Why does that cause the drive signal to appear?
Should I expect that when I install PS fets and drivers that it will still be there? EDIT: That is, the resistors are in parallel with each other, inline with B+. It's all I can do to limit the voltage.
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Scope - DMM - 460W Computer PSU - Tutorial Last edited by m4ick; 4th January 2012 at 05:24 PM. |
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#5 |
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diyAudio Member
Join Date: Nov 2003
Location: Louisiana
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What is the voltage across the B+ and ground terminals of the amp with and without the resistors in series?
What make/model 12v power supply do you have?
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Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links |
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#6 |
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diyAudio Member
Join Date: Jan 2010
Location: Gainesville, FL
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Wow, this thing is putting out close to 16v with nothing connected. Seems high.
Is this amp sensitive to over voltage? Maybe it's time to break out an old computer PSU.
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Scope - DMM - 460W Computer PSU - Tutorial Last edited by m4ick; 4th January 2012 at 05:43 PM. |
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#7 |
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diyAudio Member
Join Date: Nov 2003
Location: Louisiana
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It may be adjustable internally.
Some amps have over-voltage protection. This one likely does and 16v was just a bit too high.
__________________
Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links |
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#8 |
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diyAudio Member
Join Date: Jan 2010
Location: Gainesville, FL
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Ok, I hooked the amp to a computer power supply and I get 12.03V across B+ and -. I'm still in protect. With resistors in the B+ line it reduces to just over 5v and powers on.
__________________
Scope - DMM - 460W Computer PSU - Tutorial |
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#9 |
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diyAudio Member
Join Date: Nov 2003
Location: Louisiana
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What's the DC voltage on pins 15 and 16 at 12v in?
__________________
Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links |
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#10 |
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diyAudio Member
Join Date: Jan 2010
Location: Gainesville, FL
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This is what I get now:
01: 0v 02: 5v 03: 0.07v 04: 2.69v 05: 0v 06: 3.74v 07: 0v 08: 12v 09: .03v 10: .05v 11: 12v 12: 12v 13: 5v 14: 5v 15: 5v 16: 3.86v
__________________
Scope - DMM - 460W Computer PSU - Tutorial |
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