trouble shooting an ampeg SVT-IV with NO power?

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Curran

Well-known member
Joined
May 15, 2010
Messages
88
hey everyone. I wanted to see if any of you might be able to help me trouble shoot why my ampeg SVT-IV does not power up. This just happened at a show the other night. I pulle dthe top off and there is no smell of burning, AND all of the three fuses are still "looking" intact. where do I start on trouble shooting this thing?  thanks for any help
 
Make sure the power switch is good. I just fixed one of these a week ago. One side of the power switch was permanently open. Try moving the wires to the other side.
 
OK I am a freaking trouble shooting NOOB, HOW do I measure from the power supply? I am sure I use the horn buzz function of my DMM to check for broken components BUT where do I really start on this thing?
 
Get a schematic...

check the fuses first.... use a dmm and test continuity(beep test) across the fuses. if it beeps the fuse is good if not replace fuse with same value... Check the power switch. With the unit unplugged test continuity on the power switch pins. They should only beep in the on position. from there test according to the schematic...


 
yep switch is fine and so are the fuses. beep test proved that. so I am gonna discharge the caps and start to lift the boards out of this thing
 
Where ARE you getting power? Do you see line voltage at the power cord inside the amp? Follow the hot wire from there. You should see line voltage all the way to the power transformer. If that all checks out, disconnect the entire secondary side of the transformer. IIRC there are 3 wires going to the rectifier. 2 orange ones (?) And a yellow (?) one. The yellow is the center tap. Measure the ac volts between the two similar colored ones, then between each one and the center tap. I can't remember how the wires with the molex (or whatever) connector are setup, but you get the idea. Start at the beginning and find out what isn't behaving as it should be.
 
yeah I have been messing with it for a few days now, it is an Ampeg Bass amp that i use with my band Shatter Messiah
 
ok, I've  seen few that didnt start and later there was "nothing" wrong with and nutting burned..
iirc.turns out to be too big cap somewhere:)
 
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