Professional II JM Bridge pickup problems

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Kroc
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Professional II JM Bridge pickup problems

Post by Kroc » Mon Feb 26, 2024 11:45 am

Hi all!

I just got a Professional II Jazzmaster in dark night a week ago. It’s my first JM, and I feel like I’ve finally discovered perfection!

However, there’s one catch: the dealer gave me a good price on it because there seems to be some kind of issue with the electronics. I loved it enough that I bought it anyway (I can solder). Worst case I know I could just swap in a new prewired harness, but I really like the V-Mod II pups, the coil tap, and the series mode. So I’d rather try to fix what’s there if I can.

I was wondering if anyone might be able to help with a diagnosis:

The bridge pickup seems to intermittently cut between the normal tone and one with lots of noise, no low end, and a significant volume drop. I can ‘fix’ the problem temporarily by tapping around the screws directly below the volume and tone wheels of the rhythm circuit (series mode, technically).

On further exploration, it seems the rhythm circuit’s volume roller also isn’t working right. When rolled fully down, there’s still sound. It doesn’t seem to change the volume much at all.
I’ve also noticed that after I tap the fretboard until things sound normal, I can keep it sounding right if I keep the guitar relatively still.

If I leave it set on the lead circuit, switched to the neck pickup, I can merrily jam for hours without any problems.

I asked the dealer to look it over before purchase, and they said the bridge pickup was probably ‘on the way out’. The store is very reputable, but that still sounds like it could be a swiftly-formed conclusion from busy techs that don’t often work on the push-pull coil tap and series wiring of this particular model. Especially given the above symptoms.

I was wondering if anyone has encountered anything like this? I haven’t opened it up to dig around yet.

Thanks for reading,
Dan

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Re: Professional II JM Bridge pickup problems

Post by ldp54002 » Mon Feb 26, 2024 12:08 pm

Welcome (back) to the forum!

I ran into the same thing with my 2021 Pro II. I remember a few others mentioning similar concerns. In my case, the issue was one of the solder joints on the pickup itself; unfortunately, I can't recall which one. I also can't recall if others had found the same root cause.

So, that said, it's well worth opening it up and taking a look at every solder joint to see if anything seems loose. All I had to do was heat up the existing solder on the pickup bobbin to reflow it and all was well. If your issue is on the series/parallel switch, a quick touch-up with an iron is likely all you would need. Worst case scenario, the switch is done and you could replace it.

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Re: Professional II JM Bridge pickup problems

Post by Kroc » Mon Feb 26, 2024 1:26 pm

ldp54002 wrote:
Mon Feb 26, 2024 12:08 pm
Welcome (back) to the forum!

I ran into the same thing with my 2021 Pro II. I remember a few others mentioning similar concerns. In my case, the issue was one of the solder joints on the pickup itself; unfortunately, I can't recall which one. I also can't recall if others had found the same root cause.

So, that said, it's well worth opening it up and taking a look at every solder joint to see if anything seems loose. All I had to do was heat up the existing solder on the pickup bobbin to reflow it and all was well. If your issue is on the series/parallel switch, a quick touch-up with an iron is likely all you would need. Worst case scenario, the switch is done and you could replace it.
Hi! That's very interesting and helpful! Thank you. This is a used 2020 - perhaps it was a specific production issue with the early Pro II JMs?

I'm procrastinating opening it up, because that will mean I will have to stop playing it long enough to take the top off. ;D

I'll report back after!

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Re: Professional II JM Bridge pickup problems

Post by gibs » Mon Feb 26, 2024 1:43 pm

I know a lot of fender USA lately has had issues with bad installs of electronics. Like ground wires being smashed between the pickguard and body, and causing grounding issues. Though I’d say this sound like the bridge pickup if your hearing in the rhythm circuit (which isn’t a rhythm circuit on the am pro 2, it’s a dedicated volume and tone control with both pickups in series when activated).

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Re: Professional II JM Bridge pickup problems

Post by timtam » Mon Feb 26, 2024 6:02 pm

Here is the PDF wiring diagram for the Am Pro II JM ...
https://www.fmicassets.com/Damroot/Orig ... master.pdf

There are at least 2 errors in it, that don't match how the guitars are actually wired (the guitars are wired correctly):
- error on blue wire to push pull pot (left hand guitar's wiring diagram is correct)
- missing ground on series volume

The schematic is below. The top bout switch is more complex than the standard rhythm/lead switch on regular JMs, and IIRC there have been reports here of shorts between exposed bare wire ends at its many terminals.

But given that your issues are with the tone pot/push-push bridge coil-tap I would be looking first for bare wire shorts around its terminals. Also check the ground on the series volume pot (not shown in the PDF wiring diagram, but is apparently on the guitars). If the problems are indeed there, they should be easy to fix.

I wouldn't expect many (if any) guitar techs to know their way around this guitar. So you'd likely be paying for them to spend a lot of time trying to figure it out. But not knowing about the wiring diagram errors . Or just taking a cursory look and not actually fixing the problem. Or charging you to change the bridge pickup that probably isn't the problem.

Image
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Re: Professional II JM Bridge pickup problems

Post by Kroc » Mon Feb 26, 2024 6:45 pm

timtam wrote:
Mon Feb 26, 2024 6:02 pm
Here is the PDF wiring diagram for the Am Pro II JM ...
https://www.fmicassets.com/Damroot/Orig ... master.pdf

There are at least 2 errors in it, that don't match how the guitars are actually wired (the guitars are wired correctly):
- error on blue wire to push pull pot (left hand guitar's wiring diagram is correct)
- missing ground on series volume

The schematic is below. The top bout switch is more complex than the standard rhythm/lead switch on regular JMs, and IIRC there have been reports here of shorts between exposed bare wire ends at its many terminals.

But given that your issues are with the tone pot/push-push bridge coil-tap I would be looking first for bare wire shorts around its terminals. Also check the ground on the series volume pot (not shown in the PDF wiring diagram, but is apparently on the guitars). If the problems are indeed there, they should be easy to fix.

I wouldn't expect many (if any) guitar techs to know their way around this guitar. So you'd likely be paying for them to spend a lot of time trying to figure it out. But not knowing about the wiring diagram errors . Or just taking a cursory look and not actually fixing the problem. Or charging you to change the bridge pickup that probably isn't the problem.

Image
Thank you for sharing this! Sorry: to clarify my original wording, the tone pot/push-pull coil-tap itself actually seems to be working as intended (it's rolling off top end and switching between modes, as expected). I don't think that's at fault. It's the bridge pickup (both in the lead and series circuit; dropping out), and the volume roller for the series circuit that have problems. And again, smacking the pick guard seems to help! Lol.
Perhaps that narrows down the potential culprits?

...A little more involved than Tele circuit, that's for sure. Haha. :D

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Re: Professional II JM Bridge pickup problems

Post by andy_tchp » Mon Feb 26, 2024 6:47 pm

Dry solder joints almost for sure.

Pickups don't just 'go out' (what a ridiculous explanation from a shop).

Reflow any/all questionable looking solder joints.
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Re: Professional II JM Bridge pickup problems

Post by Futuron » Mon Feb 26, 2024 11:45 pm

Mine drops one of the pickups now and then - I forget which. Haven't been bothered to open it up, since jiggling the 3-way a bit brings it back.


I think the early ones were really rushed out the door, in the electronics department.

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Re: Professional II JM Bridge pickup problems

Post by Kroc » Tue Feb 27, 2024 8:22 am

andy_tchp wrote:
Mon Feb 26, 2024 6:47 pm
Pickups don't just 'go out' (what a ridiculous explanation from a shop).
Vibe reference:

Me at the shop: "Hi! Excuse me! I really like this one, but there seems to be a wiring issue with the bridge pickup."
Sales guy: "Let me take a look" - He reluctantly sits down and plays for about 25 seconds. Pickup acts weird, but then goes back to normal.
Sales guy: "Seems fine now!" - Hands it back. Leaves without another word, and then wanders back to continue talking with coworkers.

:fp:

P.S. To be fair, after the tech looked at it, they discounted it again past our agreed price enough for me to replace the pickup. And they were very nice, and let me play for hours without anyone coming over. But I found the above interaction highly amusing.

...I'm planning to open it up today and have a look.

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Re: Professional II JM Bridge pickup problems

Post by Kroc » Tue Feb 27, 2024 11:22 am

No luck as of yet. I reflowed a bunch of solder joints, but am still having the same issue. I notice that when I touch the screws attaching the series circuit to the pickguard, I get noise - wondering if that indicates a grounding issue? But I have tried reflowing all the ground wires attached.

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Re: Professional II JM Bridge pickup problems

Post by Kroc » Tue Feb 27, 2024 2:07 pm

Okay, I think I might have actually fixed it!!! Fingers crossed. So far so good. Documenting this here, in case it might help someone else:

I kept reflowing and going over everything repeatedly, but to no avail. I couldn't see anything obvious.
I was getting frustrated, so I took a break and did some more research. I came across this thread on Reddit:


Midway down, someone had posted this:
"KorterTwenty - 2 mo. ago
My bridge pickup had all kinds of problems with cutting out until I realized the mounting plate for the rhythm circuit pots was not firmly screwed against the underside of the pickguard. After troubleshooting everything else and pulling the pg off several times, it seemed to be just two loose screws"

I had been going over it all afternoon, and was about to close up and call it a day. But before I did, I gave the mounting screws for the series circuit a bit of extra tightening, even though it didn't seem loose.

...I put everything back together, and miraculously it seems to be working normally now. It was either that, or I finally reflowed the right wire. But either way, I've just been playing without any issues for about an hour.

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Re: Professional II JM Bridge pickup problems

Post by VANRNR » Tue Feb 27, 2024 3:42 pm

Your description of the problem was the same as what I experienced. Checked all the solders, resoldered and still found that the problem would randomly surface. The problem ended up being the switch to activate the rhythm circuit. I took the switch apart, which is not hard to do but very fiddly and has very small conductors that can get away from you. One of the conductors on mine had slipped out of place. So if your problem continues, look there. By the way, once I made this repair, I've not had any problems over the past several months.

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Re: Professional II JM Bridge pickup problems

Post by timtam » Tue Feb 27, 2024 7:36 pm

Kroc wrote:
Tue Feb 27, 2024 2:07 pm
Okay, I think I might have actually fixed it!!! Fingers crossed. So far so good. Documenting this here, in case it might help someone else:

I kept reflowing and going over everything repeatedly, but to no avail. I couldn't see anything obvious.
I was getting frustrated, so I took a break and did some more research. I came across this thread on Reddit:


Midway down, someone had posted this:
"KorterTwenty - 2 mo. ago
My bridge pickup had all kinds of problems with cutting out until I realized the mounting plate for the rhythm circuit pots was not firmly screwed against the underside of the pickguard. After troubleshooting everything else and pulling the pg off several times, it seemed to be just two loose screws"

I had been going over it all afternoon, and was about to close up and call it a day. But before I did, I gave the mounting screws for the series circuit a bit of extra tightening, even though it didn't seem loose.

...I put everything back together, and miraculously it seems to be working normally now. It was either that, or I finally reflowed the right wire. But either way, I've just been playing without any issues for about an hour.
You may have established better contact for the ground connection to the series volume pot (which also grounds the series tone cap) and the bracket. Which is one of the errors in the PDF I mentioned - the volume pot ground connection isn't shown in the wiring diagram. There should be some sort of connection between the bottom tab on the series volume pot and a ground from somewhere (maybe just the pot body /bracket connected to the grounded pickguard shielding). The bracket ground also grounds the -ve side of the bridge coil when series is OFF. So the bridge pickup wouldn't work properly with series OFF without a stable bracket ground.
"I just knew I wanted to make a sound that was the complete opposite of a Les Paul, and that’s pretty much a Jaguar." Rowland S. Howard.

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