bench testing

Monsteranus · 7th August 2011, 02:10 AM

I have a LM340T15 positve 15 volt regulator I supect to be bad. Whats the best way to bench test one of these?

Michael Bean · 7th August 2011, 02:44 AM

What is it doing or not doing that makes you suspicious?

Mike

Monsteranus · 7th August 2011, 04:21 AM

I get kind of erratic readings with my meter. It is still soldered in so I know that can give false readings.

Its in a Peavey bass amp where one of the 15 volt rail fuses is blowing. I have it out of its case on the bench. The front controls of the head are mounted on a separate chassis. I have the cables to the front chassis detached. I dont see any meter readings to indicate a direct short.

Its a 1 amp sloblow fuse. I put in a new one and power it up, it starts looking like a space heater element shortly after power up.

Michael Bean · 7th August 2011, 04:36 AM

OK, gonna need a little more to go on, it might not be the regulator that's bad. I don't suppose you have a schematic? If not, what's the model number of the amp?

Mike

Monsteranus · 7th August 2011, 01:45 PM

Mark VIII bass series 602 is the unit and the tag with a model number is MK VIII XP.

Michael Bean · 7th August 2011, 04:08 PM

No luck finding the schematic or service manual, but if you contact Peavey customer service they are usually helpful. Beyond that, is the fuse is before or after the regulator? If the fuse is before the regulator, leave the fuse out and measure the voltage, it should be a steady 35 volts or less. If it's after, leave the fuse out a take a voltage reading, do you get a stable 15 volts? If not, either the regulator went bad or something down the line took it out.

Mike

Monsteranus · 7th August 2011, 04:17 PM

Its before the regulators. Measure voltage at the fuse point for 35 or less or at the regulator? Its been a while since I have tinkered on this stuff.

Monsteranus · 7th August 2011, 04:48 PM

I sent a request for a schematic to Peavey, maybe I will get it soon.

jaycee · 7th August 2011, 05:48 PM

best way to test it is pull it, quickly lash up the datasheet example circuit for it and see if it outputs the correct voltage. if it pulls lots of current, gets hot with no load etc, it's dead. It's not likely though - they usually fail open circuit.

simon7000 · 7th August 2011, 05:51 PM

First check the diodes, then the input filter capacitor, then the output filter. You should be able to be sure they are not shorted with just an ohmmeter in circuit.

As the regulator is about a buck, I'd just replace it after those tests. While it is out check the caps again.

7th August 2011, 02:10 AM	#1
Monsteranus diyAudio Member Join Date: Nov 2010 Location: Northwest Georgia	bench testing I have a LM340T15 positve 15 volt regulator I supect to be bad. Whats the best way to bench test one of these?

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7th August 2011, 02:44 AM	#2
Michael Bean diyAudio Member Join Date: Sep 2004 Location: Minneapolis, Minnesota, USA	What is it doing or not doing that makes you suspicious? Mike

7th August 2011, 04:21 AM	#3
Monsteranus diyAudio Member Join Date: Nov 2010 Location: Northwest Georgia	I get kind of erratic readings with my meter. It is still soldered in so I know that can give false readings. Its in a Peavey bass amp where one of the 15 volt rail fuses is blowing. I have it out of its case on the bench. The front controls of the head are mounted on a separate chassis. I have the cables to the front chassis detached. I dont see any meter readings to indicate a direct short. Its a 1 amp sloblow fuse. I put in a new one and power it up, it starts looking like a space heater element shortly after power up.

7th August 2011, 04:36 AM	#4
Michael Bean diyAudio Member Join Date: Sep 2004 Location: Minneapolis, Minnesota, USA	OK, gonna need a little more to go on, it might not be the regulator that's bad. I don't suppose you have a schematic? If not, what's the model number of the amp? Mike

7th August 2011, 01:45 PM	#5
Monsteranus diyAudio Member Join Date: Nov 2010 Location: Northwest Georgia	Mark VIII bass series 602 is the unit and the tag with a model number is MK VIII XP.

7th August 2011, 04:08 PM	#6
Michael Bean diyAudio Member Join Date: Sep 2004 Location: Minneapolis, Minnesota, USA	No luck finding the schematic or service manual, but if you contact Peavey customer service they are usually helpful. Beyond that, is the fuse is before or after the regulator? If the fuse is before the regulator, leave the fuse out and measure the voltage, it should be a steady 35 volts or less. If it's after, leave the fuse out a take a voltage reading, do you get a stable 15 volts? If not, either the regulator went bad or something down the line took it out. Mike

7th August 2011, 04:17 PM	#7
Monsteranus diyAudio Member Join Date: Nov 2010 Location: Northwest Georgia	Its before the regulators. Measure voltage at the fuse point for 35 or less or at the regulator? Its been a while since I have tinkered on this stuff.

7th August 2011, 04:48 PM	#8
Monsteranus diyAudio Member Join Date: Nov 2010 Location: Northwest Georgia	I sent a request for a schematic to Peavey, maybe I will get it soon.

7th August 2011, 05:48 PM	#9
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	best way to test it is pull it, quickly lash up the datasheet example circuit for it and see if it outputs the correct voltage. if it pulls lots of current, gets hot with no load etc, it's dead. It's not likely though - they usually fail open circuit.

7th August 2011, 05:51 PM	#10
simon7000 diyAudio Member Join Date: Nov 2008 Location: Oakmont PA	First check the diodes, then the input filter capacitor, then the output filter. You should be able to be sure they are not shorted with just an ohmmeter in circuit. As the regulator is about a buck, I'd just replace it after those tests. While it is out check the caps again.

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