SE analog board - L2 width control

[smrieck511]

I have several of these boards that work fine so I know how to adjust this control. One of the width controls (L2) has no effect no matter what. Checked and reflowed all the solder joints.

is this perhaps connected to a resistor that might be shot? thanks for any help.

 

[smrieck511]

it's had a full recap by the way. I replaced C15 no difference... R19 looks like it might have something to do with it?

 

[powellb]

I have this same problem. I have tested/replaced the resistors and caps in that horizontal control circuit to no effect. It is common for the L2 inductor to break internally (the very fragile internal ferrite coil). It seems the only fix is to find a donor board and replace the inductor. I have ordered a broken Mac Plus parts board. I'm hoping that its L2 is intact and works on the SE board. I'll report back when I get to it.

 

[smrieck511]

I did manage to fix it ..luckily kept a spare analog board around. So I switched out the whole L2 inductor. Curious how difficult it would be to make one of these?

 

[powellb]

Great! I am hoping that the spare plus board I ordered will work out. It sounds like a very difficult endeavor due to the ferrite coil inside. While not precise, making something similar I believe is hard...

 

[Phipli]

If it is just a normal fixed value inductor then if you measure it, you could just buy new ones?

Are you sure that says L2 and not L3?

Sounds like it is variable though which will be more tricky to find something that fits, but they are available. Strange, the symbol does look variable.

Edit - ah, I was looking at the wrong thing. I was looking in the centre of your extract, not to the right. Especially with the mention of R19.