MB Quart RAA2400 - Page 2

mike49504 · 5th February 2010, 01:02 AM

ok this amp has 7912 and 2 7812's

on 1 side there is a 7912 and 7812 and the readings are

7912

leg1= 0
leg2= -23.62
leg3= -12.21

7812

leg1= 23.45
leg2=0
leg3= 11.97

on the other 7812

leg1=23.54
leg2=0
leg3= 0

on the outputs
leg1= 1.25
leg2= 0
leg3= -0.79

Perry Babin · 5th February 2010, 01:18 AM

For the second 12v regulator, either it's defective or something is shorting it's output to ground.

Is it possible that the power supply shut down before you had a chance to measure the voltage on the outputs?

Are there any broken legs on the rectifiers?

mike49504 · 5th February 2010, 02:04 AM

it could be possible its shutting down before i get a chance to measure voltage at outputs cause i have voltage at outputs for a split sec

mike49504 · 5th February 2010, 02:11 AM

will a 7815 work in place of the 7812 for trouble shooting?

mbates14 · 5th February 2010, 05:19 AM

Quote:

Originally Posted by mike49504

will a 7815 work in place of the 7812 for trouble shooting?

Certain amps that is not advised. I learned this the hard way by blowing out an entire op-amp complex on an amp by doing that. you can go from 7815 to 7812 with some possible early clipping and gain loss, butyou CANNOT go the other way... dont ask how i know. lol.

mike49504 · 5th February 2010, 08:39 AM

Ok i put a 7812 in this amp out of a amp that is working. still have the same problem no output and something is shorting the output on the 7812 to ground. all the pins on the 7812 lead to the output driverboard where that ic is.

could it possibly be the ic?

Perry Babin · 5th February 2010, 01:47 PM

It could be. Pull the IC out of the socket or power up the amp without the audio driver board plugged in.

With the audio driver board out, do you have an audio signal on any pin of the audio driver board connector?

mike49504 · 7th February 2010, 01:34 PM

How do i check for audio single on the pins where the driver board plugs in

mike49504 · 7th February 2010, 02:33 PM

Also wondering if you know the value of the caps in it they look like a resistor The body of it is green and the color bands on it are yellow black brown.

Any help would greatly be appericated

Perry Babin · 7th February 2010, 05:30 PM

Could you have the bands reversed? If so, it's likely a 0.1uF.

If you have your scope, check for signal on the connector where the board plugs in. If not, you may be able to determine if there's signal there with a low frequency test tone and a multimeter. The signal is on the smaller of the two connectors, if I'm not mistaken.

Did you ever get it to produce rail voltage?

5th February 2010, 01:18 AM	#12
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	For the second 12v regulator, either it's defective or something is shorting it's output to ground. Is it possible that the power supply shut down before you had a chance to measure the voltage on the outputs? Are there any broken legs on the rectifiers? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

5th February 2010, 01:47 PM	#17
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	It could be. Pull the IC out of the socket or power up the amp without the audio driver board plugged in. With the audio driver board out, do you have an audio signal on any pin of the audio driver board connector? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

7th February 2010, 05:30 PM	#20
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Could you have the bands reversed? If so, it's likely a 0.1uF. If you have your scope, check for signal on the connector where the board plugs in. If not, you may be able to determine if there's signal there with a low frequency test tone and a multimeter. The signal is on the smaller of the two connectors, if I'm not mistaken. Did you ever get it to produce rail voltage? __________________ 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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5th February 2010, 02:04 AM	#13
mike49504 diyAudio Member Join Date: Sep 2006	it could be possible its shutting down before i get a chance to measure voltage at outputs cause i have voltage at outputs for a split sec

5th February 2010, 02:11 AM	#14
mike49504 diyAudio Member Join Date: Sep 2006	will a 7815 work in place of the 7812 for trouble shooting?

5th February 2010, 08:39 AM	#16
mike49504 diyAudio Member Join Date: Sep 2006	Ok i put a 7812 in this amp out of a amp that is working. still have the same problem no output and something is shorting the output on the 7812 to ground. all the pins on the 7812 lead to the output driverboard where that ic is. could it possibly be the ic?

7th February 2010, 01:34 PM	#18
mike49504 diyAudio Member Join Date: Sep 2006	How do i check for audio single on the pins where the driver board plugs in

7th February 2010, 02:33 PM	#19
mike49504 diyAudio Member Join Date: Sep 2006	Also wondering if you know the value of the caps in it they look like a resistor The body of it is green and the color bands on it are yellow black brown. Any help would greatly be appericated

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