need ampeg guru-svt pro 4 problems

[mastervolume]

I have an older ampeg svt pro 4 that has finally let go. It stopped working on one channel after a short period of that channel cutting in and out in volume. It cut out and let out a small puff of smoke then quit on one side. I opened it up and inspected all the circuit boards and components but cant find any obvious damage or bad solder joints. I need help. Any ideas where to check next?

[JimmyM]

You won't see bad solder joints. They can still look good.

Anyway, first thing you always check in an amp with tubes are the tubes. If you have a spare 12AX7, swap it with the other ones and see if you can find a bad one. If not, then it's tech time since it could be many things.

[Jerrold Tiers]

Jimmy's is good advice... but in this case it does not apply...... except for the last line.

Tubes are good if one side works..... poweramp is all SS.

Puff of smoke is bad...... lots of possible causes, most of them not good.

tech time

[mastervolume]

I checked tubes.All were good. Any way I'm pretty sure the issue is in the power amp section because there is still output on both preamp outs. The smoke didn't smell like burned resistor or transistor. I wont get into how I know that smell. It smelled like when you make a solder connection with an iron.The amount of smoke was minimal. Is there any other way to detect a bad connection. I'm pretty good with a meter. I just don't trust too many so called repair shops. I haven't found a reliable here in Houston yet.

[JimmyM]

I should have mentioned that I wasn't an Ampeg guru when it comes to knowing what's under the hood. Jerrold is, as he used to be chief engineer for Ampeg. However, both of us know how to say "take it to a tech" very well I'm sure there must be a good one around...that's a pretty big music town.

[Jerrold Tiers]

Very possibly, the smell was from the arc as the relay opened and broke the circuit on a DC condition of the power amp..... or it could easily be some other problem.

From here, it seems pretty clear that the main problem you have is that the amp is not working right

Past that, it's pretty hard to tell without "raising the hood"..... which is why Jimmy's last line of first post applies here.

All together now..... 1....... 2.......... 3........... take it to a tech!

[mastervolume]

Originally Posted by Jerrold Tiers

Very possibly, the smell was from the arc as the relay opened and broke the circuit on a DC condition of the power amp..... or it could easily be some other problem.

From here, it seems pretty clear that the main problem you have is that the amp is not working right

Past that, it's pretty hard to tell without "raising the hood"..... which is why Jimmy's last line of first post applies here.

All together now..... 1....... 2.......... 3........... take it to a tech!

OK OK dont yell at me. lol. I've decided to take it to a local shop. I'm begining to think tube amps are easier in the long run. Thanks for the advice guys.

[JimmyM]

There's no real evidence that either tube amps or SS amps are more prone to breakage.

[cheezewiz]

Originally Posted by JimmyM

There's no real evidence that either tube amps or SS amps are more prone to breakage.

Unless you ask Seamonkey.

[grendle]

If it let the magic smoke out there is something burnt. Check all the caps, diodes and transistors on the side that blown for either an open or something burnt. Most likely a cap.I Would personally replace the component before and after the bad one for reliability purposes. If its a bad electrolitic cap or tantilum I would replace them all. When one starts to go, more usually follow. Just my .02

[Dekker]

Also, failed electrolytic capacitors can still "look" good to an untrained eye. If the top of the cap is in any way bowed upwards, it is possible that it has failed. Not all of them fail catastrophically (though I have seen a couple!)