mesa express 5:50 contour circuit does not work there is no resistance in PCB !!!!!

[thegroup98]

Hi
I have a problem with a mesa boogie express 5:50 head
purchased used in excellent condition the previous owner who bought new told me that he had a problem with the contour circuit but did not ever brought in for repairs because they cared about how in fact effect while working on his apparently the circuit not from any Equalization
now I have downloaded from this site the wiring diagram and I discovered with surprise that the resistance number "87" by 10 k indicated on page 5 of the wiring diagram is not inserted into the PCB in the two contact points, though perfectly welded is missing........ I never happened a thing especially with a product so famous ... .... anyway I tried it insert a 10Kohm resistor from 1/4 Watts but unfortunately circuit does not work the same .... evidently pursued the problem method of resistance is damaged some other component that I can't find
Sorry for my English
Thanks angelo santoro

[Enzo]

I don't think R87 needs to be there. On some other model amp that uses this board, they might install R87 instead of the contour controls. That is just my opinion.

Look at the last page for the switching circuit. You have a switch to select channel 1 or channel 2 at the top, then an on/off switch for each channel. When your channel is selected AND contour is turned on, then the 4N33 grounds the gate of one of the JFETs on page 5. When that happens, the JFET turns on and that completes a circuit through the contour control.

If your contour circuit is not working, I would first check if the control voltage at the gates of the two JFETs is turning off and on with the switches.

[thegroup98]

Thank you for your reply
the mesa is the 2006 000909 serial number
the wiring diagram is in February 2007 will be a mod. later?
I measure the voltage on JFET unless I volts could be the problem
I have not specified in the message
before you install the 10 k I inspected the underside of the PCB with a mirror
and I found a track that goes in the direction of the 4 inductors of contour that so it wouldn't be connected ..... no I can see exactly where the track ends without removing all the amplifier
I measured and then I'll let you know
Angelo