Vox Jaguar Repair Issues

[dorrisant]

I've already read through this:
http://music-electronics-forum.com/t33421/

I have one of these on the bench... Someone else had "fixed" it already. What a joke. Anyway, I rebuilt the power supply so now it comes on, passes signal, all keys and switches seem to function correctly and they all seem to be in tune but I'm not out of the woods yet. It has an ominous chord playing at a lower volume that any of the keys will produce alone, I would say about 20% volume. I scoped it and found that at idle (no keys depressed), each of the main generator cards produces a signal on Pin#4. This is the 3rd signal divider output from the dividers. This combination of notes could probably account for what I'm hearing. Before I scoped it I thought that there must be some leaky Germaniums causing the issue. I don't believe that now.

Just wondering if anyone would have an idea of what would cause this type of problem... maybe a little more operational theory? Has anyone seen this type of issue. What would cause all of these cards to produce signal on the same pin?

As a note, I haven't replaced any other electrolytic caps besides the two 1000uF caps in the power supply module (C37a&b) and the 1000uF mounted to the control board pcb (C38). I used 2200uF caps. I don't see that being the problem though. I realize that this is a -15v supply and all three of these caps are oriented correctly... no problems there.

Sorry I can't seem to figure out how to post a copy of the schematic or I would. It is on the first page of the above link though.

Thanks in advance for any help.
Tony

[DrGonz78]

Well strange symptoms indeed. As I recall you should see a signal coming off all the divider circuits outputs. So what I am saying there is that pin 4 should have a constant signal output from the tone generators as I recall (pretty sure). Pressing the keys lifts the contact off from ground and opens that individual note to produce an output. A lower note or chord seems strange that it is bleeding through. Now there could be a low resistance between the key contact and the bus bar, possibly something to check. My guess there would be to clean that metal bus bar in the hopes that it restores grounding to all of the keys contacts when not being played. Scope the output jack to see if any signal is coming out with no keys pressed.

BTW this was just thought of what it could be. Also when you clean that bus bar you push the key to lift the contact and carefully clean the metal bus bar. I had more trouble with the bus bar since my plastic pieces had snapped off and had to jimmy rig something to make it work. It is very fragile and a real pain in the A$$, so be patient when working on that part of it.

[dorrisant]

I figured it out!! The sound was bleeding through the power supply chassis. I pulled the output jacks out of the chassis and tried it that way. Viola!! No more ominous chord.

Plugged it in to my John Mayer Signature clone and rattled the windows for a while. It does sound pretty good!

Isolation washers on the way.

Thanks for the help DrGonz. I appreciate you taking a look.

Tony

Edit: The sound had a constant volume separate from the volume controls...

[Enzo]

Or replace the jacks with plastic bushing ones, which insulate by their nature.

[dorrisant]

Thanks Enzo. The customer wants "all original" or I would just use the Cliff jacks I have in stock. No biggie... problem solved.

[Enzo]

Yeah, I know. They'd rather have it original than working.

[52 Bill]

Are the output jacks original or have they been replaced?

The voice filter section uses a "signal ground" that is raised by half the dc power supply, roughly -8 volts. Perhaps the previous repair person screwed up the grounding scheme.

[dorrisant]

The jacks are original... I think you are right. The power supply was blowing fuses when I got it here. I rebuilt it and probably tied something to ground.