Ampeg BA115 q

[Jorgens]

Hi! I`m trying to fix our BA115, and took the mainboard out and re soldered it, as there were no sound at all coming out of it. When re assembling I noticed this missing screw you can see in the pic. It seems to have been one there before, and I see the screw on all pic`s I have watched, but I came to wonder; Is it there only on the US models with 115V? I`m no good at electronics, so any help is appreciated!

Cheers
Jørgen

[Mars Amp Repair]

I've never had that screw missing on the many of these amps I've serviced.
That screw is the connection of the Amp electronics ground, sometimes referred to as the 'Audio Ground', to the chassis ground. Without it there is no connection to the chassis from the amp for proper shielding. It also appears from the schemo that what some refer to as the 'Death Cap' also uses this connection to the chassis. My take on this Death Cap, which I like to refer to as the signal grounding cap is of such a low value as to couple very little of the line AC to the chassis and that only applies if there is no connection to earth ground thru the line cord. Also as a this amp is a relatively new design compared to the ones of the 50's - 70's, has been UL approved. So any risk of dangerous shock is minimal and only if there is no line cord ground available.
Now if someone with a better understanding of all this is welcome to augment or correct any of what I've stated, please do.

Bottom line is: Install the screw. It's supposed to be there.
glen

[Jorgens]

Hi, and thanks! Just what I wanted to hear I guess it's a M3 screw, but it actually seems like the threads in the chassis have been partly stripped, will find a solution. Ps; that might explain the slight discoloration of the contact from the 230V to the chassis aswell...

[Greg Robinson]

It also appears from the schemo that what some refer to as the 'Death Cap' also uses this connection to the chassis. My take on this Death Cap, which I like to refer to as the signal grounding cap is of such a low value as to couple very little of the line AC to the chassis and that only applies if there is no connection to earth ground thru the line cord. Also as a this amp is a relatively new design compared to the ones of the 50's - 70's, has been UL approved. So any risk of dangerous shock is minimal and only if there is no line cord ground available.

The cap you are referring to is C1, and is not a death cap. This is a Class Y cap, rated for line-to-earth use, and designed to fail open. These have much higher tolerance for transient voltage spikes than standard caps, and there are limits on how large a value can be used to prevent excessive earth leakage current. Similarly, C3 is a class X cap, rated for line-to-line use. These caps will bear markings showing their safety certifications, and it is absolutely imperative that correctly rated parts are used for these positions. These caps are intended as EMC compliance devices, to keep any RF/clock noise generated by an appliance from becoming "conducted emissions" and interfering with other appliances.

All that said, while the screw is important for EMC compliance, it is not inherently required for the electrical operation of the unit, and its absence does not explain the amps lack of output. From memory it is not the circuit to safety earth bond (you can test this by using a multimeter on continuity setting from another circuit ground point to chassis to confirm continuity), but it should be replaced regardless.

Jørgen, do you have much experience repairing electronics? Have you checked supply voltages?

Here's a schematic:
https://ampeg.com/support/files/Sche...(103XXC_1).pdf

[Jorgens]

No, not much, but will check that aswell. Thanks!

[Mars Amp Repair]

The cap you are referring to is C1, and is not a death cap. This is a Class Y cap, rated for line-to-earth use, and designed to fail open. These have much higher tolerance for transient voltage spikes than standard caps, and there are limits on how large a value can be used to prevent excessive earth leakage current. Similarly, C3 is a class X cap, rated for line-to-line use. These caps will bear markings showing their safety certifications, and it is absolutely imperative that correctly rated parts are used for these positions. These caps are intended as EMC compliance devices, to keep any RF/clock noise generated by an appliance from becoming "conducted emissions" and interfering with other appliances.

All that said, while the screw is important for EMC compliance, it is not inherently required for the electrical operation of the unit, and its absence does not explain the amps lack of output. From memory it is not the circuit to safety earth bond (you can test this by using a multimeter on continuity setting from another circuit ground point to chassis to confirm continuity), but it should be replaced regardless.

Jørgen, do you have much experience repairing electronics? Have you checked supply voltages?

Here's a schematic:
https://ampeg.com/support/files/Sche...(103XXC_1).pdf

Thanx Greg for that clarification. Glen - Mars Amp Repair, Now at 12th Fret Music, ID

[glebert]

Do you have sound at the headphone jack? Some of these (maybe all) route the full speaker power through the headphone cliff jack, which is dumb. These jacks can get corroded and no sound will go to the speaker.

[DrGonz78]

Do you have sound at the headphone jack? Some of these (maybe all) route the full speaker power through the headphone cliff jack, which is dumb. These jacks can get corroded and no sound will go to the speaker.

Yup I even had one where the molex style output speaker connector was not making good contact. Sort of had to heat shrink or hot glue it on there to keep the connection consistent. Not saying this was a common problem for this amp but just a common problem on any amp with those connectors.