ampeg svt-3 pro bass problem

[randysmojo]

Sorry to stir up an older thread, but does anyone happen to have a good picture or diagram of how to hook up the wires from the from power switch and transformer? I tried taking pictures before I pulled them off but my cell phone that I took the pictures with messed them up and I can not make out what goes where. My particular SVT-3PRO is a USA made blue and red logo Saint Louis Music model if that makes a difference.

Thanks!

[Jazz P Bass]

Try this link.
Google Images
Click on Full Size Image.
That will take you to Photo Bucket.
41 images of the SVT 3 Pro.
I have attached the schematic of the power supply.
Triple check your work against it.

[randysmojo]

Last little bit!!

Best I could do with pics I have and others, I got everything except the black and white wire from the transformer and two of the four wires from the switch. I got the two from the switch that plug next to where the power comes into the board. I know which two plugs each of these pairs of black and white wires go on, but don't know which wire goes where on them. Out of the two big white and black wires off the transformer, which one plugs in closest to the outer edge of the board, and same for the two smaller black and white wires from the switch. Can anyone tell me? I can't tell from the schematic what wires off the transformer go where. Please help!! I'm almost done putting it back together but don't want to guess and blow something here!!!

[Jazz P Bass]

Will you please look at the power supply schematic.
On page 3.
It clearly shows exactly "where" the wires go.
If you cannot understand the schematic, then take it to a tech who can.
Or the risk is very great of you damaging the amp & just possibly yourself.
This is why the manufacturers place that sticker on the chassis.
"Service by experienced technician"

[randysmojo]

When I originally looked at your post last night the schematic did not show up for some reason so I was stuck looking at schematics I found elsewhere that did not have that page. I actually have a degree in electronics and am more than qualified to work on things like this problem. I just thought it would be nice and easy if someone could tell me "oh ya, just hook up this wire to that one, etc" and I could be on my way. If people want to get rude, I can definitely live without their help!

[J M Fahey]

Dear randys

I actually have a degree in electronics and am more than qualified to work on things like this problem.

and

I just thought it would be nice and easy if someone could tell me "oh ya, just hook up this wire to that one, etc" and I could be on my way.

aren't compatible, please choose one and act accordingly.

By the way, yesterday I had started writing an answer suggesting you get some tecnician friend to help you, then didn't post it. My mistake.

If people want to get rude, I can definitely live without their help!

If you find it rude experienced people providing you with the correct answer to what you ask (which sometimes is *not* what you expected, and for a good reason), what can I do?

To place things in proper perspective, considering that by definition the amp makers are the ones who know it best, why don't you ask Ampeg the exact same question you posted here?
I'd *love* to read their answer.
Good luck.

PS: meanwhile, follow strictly the instructions printed in the back panel:
"No user serviceable parts inside"
"Refer servicing to qualified personnel"
"Danger of shock and fire - Do not open"

EDIT: maybe I should add that nobody is making fun out of you, quite the contrary.
We are posting this out of respect, of you and your property. (which in this case would be the amp)

[Jazz P Bass]

If people want to get rude, I can definitely live without their help!

I am sorry if I came off as rude.
I do not know you from Adam.
I am sorry also if I impinged on your electronics degree.
This forum tries to help technically oriented people.
There is no BS.
If you appear to be stumbling around in an amp, it is to everyones advantage to warn you away from the equipment.
As to the Ampeg.
Are not the J designations marked on the circuit board?
Normally the terminal headers are marked.
If so, follow the schematic.
(Yes , I know, it is not a board layout. They appear to be at a premiuim on most service manuals)

[randysmojo]

Everything is OK. I think it is all a miss understanding in a way. I couldn't see the schematic because it blended into the background color in the attachments box. Otherwise I could have gotten it all done pretty easy now that you pointed it out and I looked again on a computer with better contrast. Sorry I got a little defensive. The way I perceived the wording is probably not how it was meant.

As for J M Fahey's reply, you don't know me from Adam either. Who is it a person that might be technically savvy couldn't want an easy quick way to do it? Considering at the time I still did not have the schematic anyway? I have rebuilt vintage tube amps many times, but it's been a while for me working on electronics, so I tried to do what I thought would be the smart thing and take pictures of the wires and how they where connected. So my phone sucks and messed the pictures up. I should have used a better camera, or drawn a diagram I know, but I was so excited that I knew what was wrong with my amp that I wanted to get it fixed. I did fix the problem it was having, which was about a half a dozen cold solder joints!

I do have experience with what I am doing, but I understand that I am new to this board and no one knows me, therefor no one knows if I know anything, so I apologize to the whole board for being a little miffed the first time out. I will conduct myself better from now on!

[Jazz P Bass]

I think we all have been there (not documenting the job)
Oh, I'll remember!
It is kind of like hitting your thumb with a hammer.
You swear you will never do that again.
Glad that you got the amp up & running.
Welcome aboard.

[J M Fahey]

Congratulations on having successfully repaired your amp.

[soundguruman]

You really need to realize, it's a CRATE amplifier with the name "ampeg" stuck on the outside. It is not built anything like a real Ampeg amplifier.
When you come to grips with the actual origin of this amplifier, you will realize the problems involved. I won't work on them, because I don't want to take the responsibility.
They invented it, let them fix it. And when it fails (again), let them take the responsibility.

[soundguruman]

One thing that goes bad pretty frequently is an opto-coupler, used for limiting the amp's current.
Take it out and bypass it, no need to replace it, it will fail again.

[J M Fahey]

One thing that goes bad pretty frequently is an opto-coupler, used for limiting the amp's current.

My glasses must be very dirty, can't find it .

Would you be so kind as to point it in the schematic?

If you find it, could you please explain how does it limit this amp's current?

Thanks in advance.

[spy]

I did fix the problem it was having, which was about a half a dozen cold solder joints!

Oh yes, I remember mine when I took off the PCB, really bad solder joints everywhere! I refreshed as much I could! It's still working just fine without any problems. Take care to set the bias correctly before starting to use this amp. If you follow the link I posted, there's info on that.

And next time don't take only pictures, right everything down on a piece of paper with full details. It'll save you a lot of time!

[soundguruman]

My glasses must be very dirty, can't find it .

Would you be so kind as to point it in the schematic?

If you find it, could you please explain how does it limit this amp's current?

Thanks in advance.

I have to dig up the schematic unless somebody posts a link...
anyhow there is a photo resistor and LED on all the ones I've seen, the LED glows according to the power consumption, and the photo resistor is in the audio path. When the LED reaches a certain brightness, it starts to shut down the volume of the audio, to keep the thing from going over current BUT, the photo resistor or LED goes bad or gets out of whack, the volume drops off or fails completely.Now the amp won't work.
I recall that I used to bridge out the photo resistor, to make the thing work again.

But don't stick in a new one, cause it fails pretty fast. Better to just bypass it. Anyhow, that's one of the most common failures on this amp. I don't know if all the ones made have the same photo coupler, but the ones I've seen were shrink wrapped, the LED and resistor together, on the board.

Then if the volume dies, it usually is that photo resistor. Now that I think back. it might be a neon bulb instead of an LED, I'm trying to recall...

That schematic is a bit hard to find, could you post it or a link. I would be happy to point out the part I'm referring to.