65 Fender Champ input problems

[BrokenSkull]

in the above highlighted picture - I see that the lead of the 1M resistor is not poking through the 2 holes of the input jacks. Make sure you do that to hold the whole assembly together

then hook the 68k through there and solder it all together at once

I usually put it through the front holes of the amp backwards to get the spacing right then swing it around to the other side and thread the nuts on

I just installed two new jacks with another new resistor, made sure everything was installed as above with no change.

[BrokenSkull]

My 0.02p:

Check that the solder on the tip contact hasn't shorted the tip & switch contacts on the RH jack.

What is soldered to the sleeve contact on the LH jack?

Andy

Just replaced both jack and have the same issue. Nothing is soldered to the sleeve jack at this time.

[Structo]

Those Switchcraft jacks are like the ones I've been complaining about.

You took some great macro photos there.

See the switch contact? Make sure that is indeed making contact with the other side.

That is where the trouble lies with these jacks.

[BrokenSkull]

So where at in the circuit does jack #2 get it's signal reduced?

[Jana]

Sounds to me like either the 68K resistor on the #2 jack is bad, way too high a value or isn't making good contact on the solder connections,

or

the contact on jack #2 is not breaking contact from with the switch when a plug is inserted.

[BrokenSkull]

Sounds to me like either the 68K resistor on the #2 jack is bad, way too high a value or isn't making good contact on the solder connections,

or

the contact on jack #2 is not breaking contact from with the switch when a plug is inserted.

I've checked these, the good jack will work fine through either of the two 68K's, The problem seems to stem from the 1Meg resistor attached to jack 1, if I remove this resistor then both jacks work as they should except for the hum when the cable is removed, as expected.

[M Fowler]

Are you plugging in and testing with the jacks loose or tightened down to the chassis?

Mark

[BrokenSkull]

Those Switchcraft jacks are like the ones I've been complaining about.

You took some great macro photos there.

See the switch contact? Make sure that is indeed making contact with the other side.

That is where the trouble lies with these jacks.

I've checked these with an ohm meter and they are working as they should.

[Firestorm]

Did you change the resistors on the board?

Yes both 68K R's have been replaced with new.

Double-check the new resistors to make sure they are not 68R instead of 68K. At jack 2 you read 134.9 ohms to ground (roughly 2 x 68R) when it should be 136K (2 x 68K).

[BrokenSkull]

Did you change the resistors on the board?

Yes both 68K R's have been replaced with new.

Double-check the new resistors to make sure they are not 68R instead of 68K. At jack 2 you read 134.9 ohms to ground (roughly 2 x 68R) when it should be 136K (2 x 68K).

Good eye Firestorm, I've got 68ohm resistors installed instead of 68K, Don't have replacements on hand but will get some this afternoon and let you know what happens. Thanks!!

[Firestorm]

Good eye Firestorm, I've got 68ohm resistors installed instead of 68K, Don't have replacements on hand but will get some this afternoon and let you know what happens. Thanks!!

That would do it. There is another resistance not shown on the schematic, which is the impedance of the pickup coil itself. This forms a voltage divider with the 68Rs that attenuates almost all of your signal. When you remove the 1M resistor (and presumably the part of the lead tying the shorting contact to ground), the input's ground reference is through the coil, which works fine: see the wiring of Harvard and Vibrolux inputs.

[Structo]

With a plug inserted into jack 2, measure the resistance between the tip and ground.

Jack 2 is 134.9 ohms. jack 1 reads 1meg

I guess that should have been a clue we all overlooked, except Firestorm.


Good catch!