Motorboating in my 5e3

[Boxbie]

Hiya,

My weber 5e3 clone which I have had working (on and off) since 2009 has now started motorboating when the volume controls are high. All the controls effect the speed/volume of the motorboating.
There is also wicked hum in the normal channel.
I've changed out all the tubes, which has had no effect on the problem.

Where do i start?

Thanks in advance

[madkatb]

When in doubt ask R.G.
Motorboating
Excessive Hum
Looks like you need new power supply caps.

[loudthud]

Check / clean / re-tighten the input jacks and pot nuts. Also, any transformer bolts used for ground lugs.

[Chuck H]

+1 to both.
Power supply caps SHOULD still be good since they're only three years old. But that's no guarantee that they are. A bad ground, most likely in the power supply, is always a good suspect with your symptoms.

[Boxbie]

Cool thanks guys. I will take out the chassis, tighen everything, and reflow the solder in all of the preamp section and the power filtering section.

I should mention that in January I completely gutted the amp, and replaced the eyelet board with a fibreglass turret board and replaced all the discrete components (big electrolytics, resistors, everything).
So I don't think any individual component should have failed from old age (but who knows!).

I'll report back after the basic reflow and tightening. Thanks again

[Boxbie]

Ok, so i have tightened all the bolts, pots and jacks. none of them were loose.
I've reflowed the solder on all the joints on the board. I'm still getting the motorboating a certain settings.
What should I look for next?

Thanks!

[Chuck H]

Have you tested all the grounds? Especially the filter cap grounds. Also test that all the filter cap + leads have a zero resistance path to their respective plate loads. If all checks out get a 22uf/450V cap and solder an aligator clip (the kind with rubber insulation) to each terminal. Then clip it across each filter cap one at a time testing for the problem. Remember that the cap will be charged after it's clipped into the circuit, so don't shock yourself. If clipping the cap across any of the existing filters stops the problem, replace that filter cap.

[Boxbie]

Will do. Thanks!

[dragonfly66]

Have you tested all the grounds? Especially the filter cap grounds. Also test that all the filter cap + leads have a zero resistance path to their respective plate loads. If all checks out get a 22uf/450V cap and solder an aligator clip (the kind with rubber insulation) to each terminal. Then clip it across each filter cap one at a time testing for the problem. Remember that the cap will be charged after it's clipped into the circuit, so don't shock yourself. If clipping the cap across any of the existing filters stops the problem, replace that filter cap.

Thanks for the info, this helped me! I found the issue with the motorboating in my 5E3 by using this method of alligator clipping a 22uf cap across the existing caps.

[Boxbie]

Hey thats great! I can’t remember what I did. I may have taken it to a real tech. But I have had a lot of the big spragues go bad and I dont use them anymore.