Mtx 6500d

mike49504 · 17th January 2010, 05:23 AM

I got this amp in to repair. THe amp powers up but no output. Its not producing rail voltage. I checked the voltage at thr rectifiers and very low voltage.

I then checked the tl494 and the voltages read

1=2.37
2=2.37
3=3.53
4=1.13
5=1.48
6=3.29
7=0
8=13.33
9=0
10=0
11=13.33
12=13.33
13=4.90
14=4.90
15=4.90
16=0

Wondering whats the next step to get this amp working

Perry Babin · 17th January 2010, 05:32 AM

I think that pins 1 and 2 are for the regulator and it appears that the rail voltage is precisely what it should be. Precisely what is the DC voltage on the center legs of the rectifiers?

Place the black meter probe on the amplifier's ground terminal.

mike49504 · 17th January 2010, 06:24 AM

meter does nothing 0 volts and -0 volts on center leg of both rectifiers black probe on amps ground

Perry Babin · 17th January 2010, 06:38 AM

Are you sure the meter is on DC volts?

Look at the attached image. It shows how the rails are connected to the voltage dividers. Unless the IC is shorted internally causing the two terminals to have precisely the same voltage, the amp has to be producing rail voltage. The voltages in the second image are from a 6500D in good working order. You can see that the voltages are almost identical to yours.

mike49504 · 17th January 2010, 06:45 AM

Im 100% positive the meter is set to dc volts if i put red probe on amps positive terminal and black on ground terminal i get 13.89 volts

black probe on amps ground terminal red probe on fep1620ct's middle leg =0 volts

black prob on ground terminal red probe on fen1620ct's middle leg -0 volts

Perry Babin · 17th January 2010, 06:46 AM

What do you get if you put the meter on AC volts and touch it to the outer legs of the rectifiers?

mike49504 · 17th January 2010, 06:48 AM

Ok pulled the board out re did some solder connections

Fep1620 = 59.6 volts on center leg

Fen1620 = -59.2 volts on center legs

But amp has no output

Perry Babin · 17th January 2010, 06:56 AM

OK. Regulated voltage on ALL op-amps?

Gain at max?

mike49504 · 17th January 2010, 07:13 AM

im getting similar readings on all op amps besides 1 and that reads

1=0
2=0
3=0
4= -17.80
5=0
6=0
7=0
8=17.85

This op and is located behind the push switch by the gains

Perry Babin · 17th January 2010, 07:26 AM

How is this one different from the others?

Did you check the gain to make sure it was not at 0 gain?

17th January 2010, 05:23 AM	#1
mike49504 diyAudio Member Join Date: Sep 2006	Mtx 6500d I got this amp in to repair. THe amp powers up but no output. Its not producing rail voltage. I checked the voltage at thr rectifiers and very low voltage. I then checked the tl494 and the voltages read 1=2.37 2=2.37 3=3.53 4=1.13 5=1.48 6=3.29 7=0 8=13.33 9=0 10=0 11=13.33 12=13.33 13=4.90 14=4.90 15=4.90 16=0 Wondering whats the next step to get this amp working

17th January 2010, 05:32 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	I think that pins 1 and 2 are for the regulator and it appears that the rail voltage is precisely what it should be. Precisely what is the DC voltage on the center legs of the rectifiers? Place the black meter probe on the amplifier's ground terminal. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

17th January 2010, 06:46 AM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	What do you get if you put the meter on AC volts and touch it to the outer legs of the rectifiers? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

17th January 2010, 06:56 AM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	OK. Regulated voltage on ALL op-amps? Gain at max? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

17th January 2010, 07:26 AM	#10
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	How is this one different from the others? Did you check the gain to make sure it was not at 0 gain? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links


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17th January 2010, 06:24 AM	#3
mike49504 diyAudio Member Join Date: Sep 2006	meter does nothing 0 volts and -0 volts on center leg of both rectifiers black probe on amps ground

17th January 2010, 06:45 AM	#5
mike49504 diyAudio Member Join Date: Sep 2006	Im 100% positive the meter is set to dc volts if i put red probe on amps positive terminal and black on ground terminal i get 13.89 volts black probe on amps ground terminal red probe on fep1620ct's middle leg =0 volts black prob on ground terminal red probe on fen1620ct's middle leg -0 volts

17th January 2010, 06:48 AM	#7
mike49504 diyAudio Member Join Date: Sep 2006	Ok pulled the board out re did some solder connections Fep1620 = 59.6 volts on center leg Fen1620 = -59.2 volts on center legs But amp has no output

17th January 2010, 07:13 AM	#9
mike49504 diyAudio Member Join Date: Sep 2006	im getting similar readings on all op amps besides 1 and that reads 1=0 2=0 3=0 4= -17.80 5=0 6=0 7=0 8=17.85 This op and is located behind the push switch by the gains

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