Help and ideas for repairs to Ampeg B2r

[cscarpenter]

I'm the bassist in a Nashville band with a lot of shows coming up, and I'm flat broke having just moved into a new place. My amp works for a while, then begins to cut in volume and becomes dirty. I have noticed when I tap it (specifically in the center) it comes back. So my thoughts are that something is loss, or going out. I have checked the fuse, replaced all cables, plugged my bass into multiple other amps, and all of the other basic stuff. What would be bad, but still allow a distorted signal?

[stingray_65]

what amp?

make and model would help.

in general first thing comes to mind is the tube sockets need cleaned/ retentioned

Ray

[Enzo]

Look at the thread title.

First suspects are jacks - FX loop jacks, powr amp in jacks, headphones jacks, etc. RUn contact cleaner through them

[cscarpenter]

The model is the Ampeg B2R E. And it's solid state. Wish it where tube...

[stingray_65]

oops

I should use my glasses when I'm on the computer. I thought I read "help and Ideas for repair to AMPLIFIER"
Mia Culpa

[cscarpenter]

Yeah day three I've got it out on my table again. I guess I'm going to start the reverse engineering process. I have found that if I tap the main board ( stamped JB9 ) this makes it come back in... Wish me luck. I need to find a chat-room for this sort of thing so that I can have technicians talking to me like I'm defusing a bomb screaming at the top of their lungs that I'm removing the wrong line...

[Jazz P Bass]

Ampeg B2

Just my 2 cents worth. Look at the soldering of the biggest components.
If the joints look flat, you really should attempt to resolder the board.
The solder should flow up the component lead. Miniscus is the word, I think.
Well over half of my repair jobs call for resoldering.

[cscarpenter]

You mean on the bottom of the board (side facing down )?

[Jazz P Bass]

Miniscus

Yeah, look on the bottom & the top. Obviously you cannot see under the big capacitors. Look around. If tapping changes the amp, I would surely suspect bad soldering.

[cscarpenter]

There is a gel like goo around a lot of the resistors and capacitors. I know techs use it to hold electronics in place, but if used in excess should I be concerned about the amp being ''jerry'' rigged?

[cscarpenter]

So I have completely removed the big board without disconnecting the wire harnesses, and have started to check all of the soldering points. They all appear to be fine, but then again I'm not really sure what to look for other than a stem.

[cscarpenter]

Someone actually just suggested checking the "Bias resistors" and asked me if my output buttons where set correctly? I'm assuming that they mean the buttons that say -20 db / 0 db and pre/ post. All I use with this head is a r.m. compressor and a r.m. tuner. So what should those buttons be set to, and could that affect anything?

[Mark Black]

Here are some examples of some solder joint cracking in various stages from advanced to subtle (not in an Ampeg but indicative of what you are looking for) - having had experience with Ampegs made over the last couple decades or so I would bet there are solder cracking issues in a few places - especially at the multipin headers which the ribbon cables plug onto.

Use magnification & lots of light when inspecting.

http://amp8.com/tr-amp/hitachi/etc/jpeg/8500-u.jpg

http://www.jamma-nation-x.com/jammax...oldercrack.jpg

http://home.comcast.net/~tatng/Auto/MainRelay-5-cracked-joint.JPG

http://www.rangerovers.net/repairdet...rackjoint1.jpg

[Enzo]

Please humor an old tired man, check your loop jacks.

You have not only the FX loop jacks, but also the preamp out and power amp in which work the same as a loop. if the return jack on either pair gets electrically dirty at all, it can cause exactly what you complain of. Take a spare cord and plug it from send to return at the FX loop. Take another cord and plug preamp out right back to power amp in. Does that stop the problem?

or from the inside, look at the row of loop jacks across the rear - four of them in a group. Unless these are the ones with the white plactic cover - which can be peeled off - you can see the contacts. They are metal strips crosswise to the plug. As the amp is doing its bad thing, gently press down on each strip - the ones that touch the tip of a plug if one were in them. Does that make a difference?

[Mark Black]

Please humor an old tired man, check your loop jacks.

Oh yeah - and what Enzo said (twice).