1966 Bandmaster Blues

[jezzbo]

I've been tracing the first preamp from inputjack until the 500PF (coupling?)cap at the phaseinverter.
Continuity through everything. (except the caps)
So I think that there is maybe a leaky cap.
I don't think it's in those tonestack cap since it seems unlikely that the would stop working all 3 at the same time.
So therefore I think it is the 0.047uF couplingcap that is broken. (leaky, shorted?)

Anybody that knows how to test this?

Thanks

[selloutrr]

read OHMs between the leads of the cap it should be greater then 15K this is just a simple good / bad test and does nothing to test for sound quality.

[billyz]

You have already measured the voltage (DC) on one side at Pin 6 I believe. 259 VDC. lift the the other side of the cap off the board and measure for DC Volts. Theoretically should not be any. That cap is a Signal coupling cap and should only pass AC. Also, Try the POP test again , right at the capacitor side connected to the 100k Plate resistor. Then try it on the other side.

Also, Go back and insert a 1/4 jack into the the channel and try testing the input grid again.

[jezzbo]

read OHMs between the leads of the cap it should be greater then 15K this is just a simple good / bad test and does nothing to test for sound quality.

When measuring with the black probe on the ground side of the cap and with the red probe on the other side, it reads infinit Ohm.

When I reverse the probes I get a -2,52M Ohm.
(more or less the same value on every cap)

More testing tomorrow. I really need to get some sleep.

thanks

[jezzbo]

Ok guys, the normal channel works!
Yesterday I resoldered several points.
There where a lot cold solder points (still need to do some)
And now it works. and sounds nice.

Thanks for your help!

Next will be the tremolo ticking.