Ampeg bass amp

[Valvehead]

Have a Ampeg BA-115 combo here with no output. It does power up and has good dcv to the 2 output chips.

I pulled the board and fixed a few cracked joints and fired it up. It had normal signal for about 2 seconds, then went silent.

I just cant find anything wrong --ive poked and moved everything looking for a bad connection. All the 8 pin IC chips have +16 / -16v at them and arent getting hot.

Tonight i will rig up something to see if the DI xlr out works.

where would you start on this?

I dont have a scope.


http://el34world.com/charts/Schemati..._Schematic.pdf

[Valvehead]

i just noticed the scem has test point voltages--ill check all those

[glebert]

Just fixed one of these the other day with similar problem. The headphone jack also does the speaker cutout (the return to ground) and it is pretty flimsy. Considering how hot this amp runs I think it weakens the switchjack springiness. Push down on the shield tab and see if you get an output. I tried bending the tab down and cleaning it, and it would work for a while and then start flaking out, probably because of self-heating. I think running 100W of power through a cheap switchjack is a bad idea. I put in a toggle switch and ran wire to the ground, which the PCB doesn't have a great place to do that either but at least it runs now.

[Valvehead]

Ah-ha....i think you are right--the ground tab on the headphone jack is much darker...like it got hot...i was able to ground it and had signal ! Thanks ! New jack ordered