Monday, March 26, 2018

And it's back together . . . .

Well . . . it's back together.

Body cavity lined with copper (in progress) . . . check


Wiring complete . . . check


Tune up, let it rest a bit and redo the action & intonation . . . working on it . . . 


Ok it was a little more complicated than that . . . 
. . . there was a faulty switch in the neck PU coil selection unit that took me a while to run down, though I learned a new trick soldering switches . . . or maybe relearned an old one. 
. . . the original placement of the treble bleed prevented the guard from falling into the right place . . . and then when bent to a more 'convenient position' shorted out against the copper lining.
. . . when testing the resistance readings got really weird . . . due to a inversely wired tone pot . . . and then the volume pot behaved weird (see below).
. . . and then there is the switch in the tone circuit that behaves . . . not like it should . . . despite testing OK . . . 3 times . . . there seems to be some kind of 'non continuity' there that prevents the tone pot from correctly shunting signal to ground via the cap . . . which may be a wiring fault . . . 

The coil selection (where I though I had a wiring fault) now works flawlessly; GOOD. The treble bypass is quite subtle but noticeable. However, my trim pot went missing so I'll have to redo that part once a replacement comes in; OK. And then there is the tone knob . . . I think I have another faulty switch there - despite the fact that it seemed to check correctly - as there is something weird going on, I get (almost?) no tone rolloff when I have it in the prevolume position, while it - occasionally - DOES work when in the postvolume position . . . SO . . . that's another thing to check out . . . . . 

OH and this IS the LAST time I do anything this COMPLICATED . . . . . . . . . . . . the rewire took two solid days of work to complete . . . . . . 

. . . and there is something WEIRD on the volume pot; if you measure resistance between the IN & OUT lugs of the volume pot when wired up the resistance goes from 0 to 480K (or so) when turning the wiper and then on the last 5% of the range or so DROPS almost instantly to almost 0 on one of my multimeters . . . . the pot itself is fine . . . I unwired and rewired it twice thinking I had damaged it in soldering the leads . . . it behaves as it should but there is something WEIRD going on in the circuit . . . I'll have to see if I can run down next time I get the guard off.




Tuesday, March 20, 2018

Stupid mistakes . . . and a redo of the wiring diagram ... again

AND . . . one more time


OK so I managed to do a number on myself with the last revision of the coil selection switches . . . it was WRONG (mea maxima culpa) so that's been corrected - thanks to another question about humbuckers and series switching, I should trust myself a little more . . . SD humbuckers connect red to white for series . . . and that just wasn't happening before. The tone stack has also been revised. The 'grease bucket' (tm)  circuit has been removed as I couldn't figure out how to build it and a regular tone circuit on the switch ... I'll try that one again when I have some more time . . . AND . . . I wanted to try a treble bleed from the beginning so that's in there now with an on/off switch so I can see what and how much it does.

Making progress . . . . .
. . . . so far all the checks seem to come back as they should.

Left to do, build the treble bypass, finish the tone switch & knob . . . . . and wire it all to the jack. And ... transfer the harness to the actual pickguard and wire in the pickups . . . .


Oh and it turns out that guitar making IS a transferrable skill.

Tuesday, March 13, 2018

And ... another rewire . . . .

OK, after a while the neck pickup in the JM developed an annoying ... seemingly unreproducible problem . . . scratchiness . . . anyway it was painfull to listen to SO back to the diagram and trying to find WHERE I went wrong . . .

Well no faults leading to scratchiness were found . . . BUT . . . it look like the humbucker coils were wired out of phase . . . OUCH . . . start and end somehow got interchanged on the P90 part of the pRails.

EDIT / UPDATE: NO, no, NO . . . they were NOT . . . it's now been corrected in the next post

OK so here is the new diagram . . . and apologies to anyone who tried it . . .


So I took the whole instrument apart and . . . well in the end I think that an non insulated ground wire in the pickup coil switching circuit occasionally could make contact with the hot signal from the neck pickup depending on the vibration and other factors . . . not solid contact mind you, but just kinda glancing off of it ... thus the scratchyness . . . ??? . . . that's the only thing I could find remotely problematic electrically . . . and of course . . . it's hard to see through a solid wood body or pickguard and things undoubtedly move on installation and . . . . 

Also took the opportunity to rout out some 'tight spots' where the pickup legs were a 'tight' fit and to rout a shorter path from the bridge pickup to the coil switching circuit in the upper horn . . . and debating whether I want to coat the whole interior with copper shielding foil while I have it apart . . . 

Anyway here are some shots of work in progress:

First shot is the coil switching circuit being built. The second has the coil switching circuit and the phase switch complete and the rotary pickup selector switch is being built. No cloth wire this time, it's not bad to work with but I didn't have enough for a complete rebuild and it's more bulky than the silicone insulated hookup wire.


Volume & tone next week, I have to have a look at the tone circuit before I put that in (EDIT: done that and yes there was a mistake that has been corrected), the SPDT on/off/on switch should switch the tone circuit before or after the volume pot . . . just to try if it make a difference (quite possibly not), the other switch should give me a straight cap like a normal tone circuit OR a version of the Fender grease bucket circuit . . .