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JTV wiring and electronics questions.


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I have done a bunch of JTV transplants. 8 so far. However I don't do the actual work. . lol. I send them to luthiers and techs. However with all thos xplants I have some extra parts laying around. I am trying to figure out what I can cobble together from these parts.

 

I am pretty sure I have 2 of the VDI output assemblies, 1 or 2 battery boxes, A few of the JTV 59 switches but I need to swap them into some xplants that are exhibiting flakiness with the switches. I have one JTV69 main board and one JTV59 main board. I assume they work, but not 100% sure. I have just aquired 2 JTV 89 wiring harnesses with the knobs and pots.

 

I remember some threads where people way more knowledgable than I am were commenting on how all this stuff works. I have a bunch of questions, and I am sure will have more, but off the top of my head:

 

1- are the main boards actually the same? In workbench there is no distinction for each model, so I am thinking the wiring harness and switches sort of determine how the guitar acts, 59, 69 or 89 etc?

 

2- I recall reading that the "super switch" works by sending particular resistance values down VDI? If that is true would I be able to hack a different super switch to work? I am thinking the stew mac 6 way LP type in place of the 5 way on JTV69 and 89.

 

3- what is actually needed for the guitar to function. I think I have read that if no controls were hooked up, the guitar can still be controlled via POD or Helix. I rarely if ever change models or tuning via guitar, always from POD and Helix. I rarely use volume and tone at all. Though using them as expression pedals with Helix is way cool.  I have a lap steel with JTV 69 "guts". If I could borrow back the cabling harness and pair it with my JTv 69 main board, I can build another guitar. Planning LP custom 3 pickup BUT, would love to not have to put a 5 way in a Les Paul and instead use another switch. Worst case I save the JTV69 stuff for parts or backup, or build another 3 pickup type guitar somewhere down the road.

 

4-JTV 89 control harnesses have 5 way switch. I need to see how they are wired. May work as they are. Thinking maybe a double cut LP with 2 mini humbuckers or tradition humbuckers with coil splits and control as 89 does.

 

I am sure those questions will create more questions, lol. Thanks for any info you guys may have. Gonna pots a "family pic" of these xplants in another thread.

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I have a feeling that the main PCBs are physically identical in that they're built on the same production line.  However, it seems reasonable that there is a mechanism for telling the firmware which instrument it's running on.  I'd imagine this is done either by jumpering pads on the board with chip resistors or possibly through the bootstrap portion of the firmware. 

 

Explanation:  Any device that can be re-flashed must have a small bit of software called a bootstrap loader to give it enough "smarts" to communicate with the outside world and accept new operating software (like when you connect to Line6 Monkey).  The loader is typically installed at the factory by connecting an in-circuit programmer to a special set of contacts on the board and directly writing it into a "safe" location that won't be overwritten by the firmware.  It would be very simple to code the guitar type into that bitstream. 

 

If I had to guess, I'd say this how Line6 is doing it - less trouble than customizing final board fabrication. But, it also means that you are very unlikely to be able to change it.  Even if you are able to obtain the correct programmer it's not a sure bet that you'd be able to read back the bitstream (there's often a protection bit that can be set by the manufacturer).

 

BTW, accidental corruption or erasure of the bootstrap loader is often the underlying problem when a device gets "bricked". 

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"Gee, I hope all the transplants were done by one of the only 4 or 5 qualified people in the western hemisphere... ;) "----

 

You remembered. :)

Well, at least the four or five that I trust to anyway (outside of some Tyler and Line 6 guitar people).

I'm sure there are more out there, I just don't know who they are yet.

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Gee, I hope all the transplants were done by one of the only 4 or 5 qualified people in the western hemisphere... ;)

 

Turns out only 7 were real transplants. One is a stock 69 body that was refinished, new neck, new pickups, new pickguard, new tuners.

 

That one and the first four xplants were done by guitartex in san antonio. I don't know if he was qualified back then, but he is likely the most qualified in the world now having done four of them;-)

 

The last three were done by a local guy in santo domingo where I live. Third world country and they turned out fine. The first was a flying V which created problems as the wiring wasn't long enough to make it. It all had to be extended. Plus a Graphtec TOM bridge with Bigsby B5. Took a few tries but working fine now.

 

I have a new local luthier that is sanding off finish of two ebay purchased warmoth bodies. He is picking up an empty JTV59 to be able to make templates for routing etc.I will have those guitars routed and painted so they are ready for any new electronics I will yank from used JTV 59s I may come across.

 

Though we may just have to mess around with my lap steel which was a JTV69. If I can pull the cable harness out and she still functions, I hook up that harness to a JTV69 main board, battery box and output jack I have. My only issue with using those in a LP custom 3 pickup would be, not wanting a five way switch. Would rather have a LP type 6 way, or just put a switch for the mags and control the variax from Helix or POD.

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Turns out only 7 were real transplants. One is a stock 69 body that was refinished, new neck, new pickups, new pickguard, new tuners.

 

That one and the first four xplants were done by guitartex in san antonio. I don't know if he was qualified back then, but he is likely the most qualified in the world now having done four of them;-)

 

The last three were done by a local guy in santo domingo where I live. Third world country and they turned out fine. The first was a flying V which created problems as the wiring wasn't long enough to make it. It all had to be extended. Plus a Graphtec TOM bridge with Bigsby B5. Took a few tries but working fine now.

 

I have a new local luthier that is sanding off finish of two ebay purchased warmoth bodies. He is picking up an empty JTV59 to be able to make templates for routing etc.I will have those guitars routed and painted so they are ready for any new electronics I will yank from used JTV 59s I may come across.

 

Though we may just have to mess around with my lap steel which was a JTV69. If I can pull the cable harness out and she still functions, I hook up that harness to a JTV69 main board, battery box and output jack I have. My only issue with using those in a LP custom 3 pickup would be, not wanting a five way switch. Would rather have a LP type 6 way, or just put a switch for the mags and control the variax from Helix or POD.

 

I have a feeling that the main PCBs are physically identical in that they're built on the same production line.  However, it seems reasonable that there is a mechanism for telling the firmware which instrument it's running on.  I'd imagine this is done either by jumpering pads on the board with chip resistors or possibly through the bootstrap portion of the firmware. 

 

Explanation:  Any device that can be re-flashed must have a small bit of software called a bootstrap loader to give it enough "smarts" to communicate with the outside world and accept new operating software (like when you connect to Line6 Monkey).  The loader is typically installed at the factory by connecting an in-circuit programmer to a special set of contacts on the board and directly writing it into a "safe" location that won't be overwritten by the firmware.  It would be very simple to code the guitar type into that bitstream. 

 

If I had to guess, I'd say this how Line6 is doing it - less trouble than customizing final board fabrication. But, it also means that you are very unlikely to be able to change it.  Even if you are able to obtain the correct programmer it's not a sure bet that you'd be able to read back the bitstream (there's often a protection bit that can be set by the manufacturer).

 

BTW, accidental corruption or erasure of the bootstrap loader is often the underlying problem when a device gets "bricked". 

Thanks for the info. Now I remember you are certainly one of the guys that knows way more than I do.

 

The part that piqued my imagination was in workbench the guitars are not differentiated. Just JTV variax. So to me it seems almost like the same board. The variax side is the same, but the pickups and switching scheme are different. Doesn't look like that would require different boards for each model.

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Yup - same boards with either different jumper settings or low-level software initialization (probably the latter).  Would be interesting to see some hi-res photos of a 69 and 59 or 89 board side by side to see if there's anything obviously different besides data coding (I bet not).

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Yup - same boards with either different jumper settings or low-level software initialization (probably the latter).  Would be interesting to see some hi-res photos of a 69 and 59 or 89 board side by side to see if there's anything obviously different besides data coding (I bet not).

I am traveling but can certainly do that once I get home in about 2 weeks. Though posting pics on this forum is a PIA, lol.

 

I may also pull all the knob connections off the lap steel and see what if anything still works.

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Hmmm wonder if the boards in the Standards are the same. I hope they are not in some "coffin" assembly like the old Variax 300/600. I doubt it as they have mag pickups. I see good deals on standard, b stocks from time to time. Only problem is I prefer two pickup guitars over 3 pickups most of the time, at least as far as xplants go.

 

To think the first 3 JTVs I bought were all 1300-1500. Since then I have got them cheaper and mostly used. Even bought the parts off a guy that wanted just a JTV59 as a "normal guitar".

 

Last christmas I put back together two JTV 69s without the "guts". Gave one each to two nephews in the dominican republic. I also gave a younger one an epi mini flying V and all three got Zoom G1ONs. Those lil zooms are incredible for like 70 bucks.Both are learning but one is learning faster as he is more into it and lives nearby. For beginners in a third world country they have guitars and pedals that are way better than most learned on. Better than my first guitar as well.

 

I also have a JTV59 put back together without the guts. Harder with 59s as I used the bridges on three of the xplants. I think I have a bridge or two laying around, since two guitars got graphtec TOMs. I will likely try and change the stock JTV bridges for Graphtecs as well as they just sound better.

Problem is the posts are slightly different. Not sure I want to have the holes drilled bigger so may resort to modding the graphtec bridges. Have a 59P goldtop getting reassembled with it's original bridge, and may do a 13 pin or just leave it as a very decent LP copy with p90s.

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