JBL S3900 replacement crossover help requested

[mstanley117]

Hey there folks,

I have a pair of JBL S3900 that I recently acquired, and it seems that in one of the speakers the upper frequency crossover recently decided to malfunction recently.

The symptoms are that the mid range/treble compression driver has lower output than the other speaker. After taking apart the speaker (not fully) and testing the upper frequency crossover I found that by bypassing the crossover I got much higher output from the midrange compression driver. A visual observation of the board did not find anything out of place, no bloated caps, nothing looked like it had burn marks or poor connections, all the parts were there, and none of the solder joints were loose.

I've tried to do some searching around, and I have had minimal luck in finding a replacement crossover. I found the service manual with the part # (400-0479-001 / XOVER, UHF/HF - S3900), but I have had no luck finding this available anywhere.

I'm going to try reaching out later this week to JBL to find out if they have anything, and I've also contacted some other parts dealers as well as a somewhat local JBL dealer (https://www.safeandsoundhq.com/). That being said, has anyone had any luck finding replacement parts or could point me in the right direction?

Worst case scenario, the service manual has the individual parts lists / specs and the schematic, so I could re-build the crossover myself (which it may come down to), but my electronics skills aren't exactly top notch haha. For those of you that have built crossovers, what's a good online supplier for electronics in this case?

Edit: Also, in case anyone was wondering, here's the parts list for the upper frequency crossover:

Spoiler: Parts List

C1 5.6 uf 5% 100V polypropylene
C2 7.5 uf 5% 100V polypropylene
C3 1.5 uf 5% 100V polypropylene
C4 3.9 uf 5% 100V polypropylene
C5 1.2 uf 5% 100V polypropylene
C6 1.2 uf 5% 100V polypropylene
C7 1.5 uf 5% 100V polypropylene

L1 2.0 mH 5% air core DCR = 0.9 - 1.1 ohm
L2 0.06 mH 5% air core DCR < 0.2 ohm
L3 0.3 mH 5% air core DCR < 0.4 ohm
L4 0.2 mH 5% air core DCR < 0.3 ohm
L5 0.45 mH 5% air core DCR < 0.5 ohm
L6 0.036 mH 5% air core DCR < 0.15 ohm
L7 0.091 mH 5% air core DCR < 0.25 ohm

R1 15 ohm 5% 5W Metal Oxide
R2 18 ohm 5% 5W Metal Oxide
R3 18 ohm 5% 5W Metal Oxide
R4 18 ohm 5% 5W Metal Oxide
R5 15 ohm 5% 5W Metal Oxide
R6 2.4 ohm 5% 5W Metal Oxide
R7 3.0 ohm 5% 5W Metal Oxide
R8 3.9 ohm 5% 2W Metal Oxide
R9 1.5 ohm 5% 2W Metal Oxide

Best,

 

[AdamG]

Hi @mstanley117 , relocating this post to this section in the hopes that you will get some help with this issue. Good luck Sir.

 

[mstanley117]

Hi @mstanley117 , relocating this post to this section in the hopes that you will get some help with this issue. Good luck Sir.

Thank you!

TL;DR - I resolved this issue by re-seating the diaphragm inside of the JBL 175d-3 and tightening one of the binding posts. This was likely a loose connection. Unfortunately, I didn't figure this out until after I had replaced other parts.

I'm going to try reaching out later this week to JBL to find out if they have anything, and I've also contacted some other parts dealers as well as a somewhat local JBL dealer (https://www.safeandsoundhq.com/). That being said, has anyone had any luck finding replacement parts or could point me in the right direction?

Reaching out to JBL, btw, was a complete waste of time. They don't sell any parts for the "consumer" speakers, and they wanted me to ship the speaker to the nearest authorized JBL repair facility to get this resolved. This would have been probably $1,000's after all was said and done (I would need to ship to Syracuse NY in my case). So if anyone else has an issue like this, don't even bother reaching out to JBL unless you have their "professional" line of products.

That being said, The Speaker Exchange has been super helpful and has gotten me all the parts I need so far.

The good news is that I've resolved this issue. What was the issue? Likely a loose connection with the diaphragm in the JBL 175Nd-3 compression driver. While I'm very glad I've resolved this issue, it hasn't been without quite a bit of effort. This effort was where the fun and aggravation stemmed from, and I often felt those feelings at the same time haha.

What did I test / do?

First I started with REW measurements using a UMIK-1 that I've had for over 5 years now. What I measured was a reduction in the mid range compression driver (JBL 175Nd-3) of about 10-20db relative to the other speaker. I took apart the speaker (including the horn assembly, which is unscrewed from inside of the speaker where the assembly connects to the wood box.

Once I had this apart, I measured the compression driver which resulted in 3.9 ohms of resistance which is within spec (3.7 DC ohms). I thought this was good news since that I meant the driver was good, and so I focused on the crossover network instead. None of the original parts were "bad" (they all measured close to tolerance), however, bypassing certain crossover parts while running a signal resulted in improved output of the driver. This is what led me to (incorrectly) thinking that crossover parts were the issue. I ended up replacing all of the caps and resistors on the circuit board with the same (or very similar) replacements. I used Solen caps and metal oxides resistors. Parts Connexion was my go-to place to get these replacement parts.

Unfortunately, replacing the crossover parts didn't do anything beneficial for me. I even swapped the crossover from the "good" speaker, and that did not improve anything either. The weird thing was, running full unfiltered signal to the compression driver resulted in strong output, so I did not know what to do next.

At this point I was out of ideas, and the only logical next step was to take a peak inside of the compression driver in question. I carefully disassembled the rear of the driver exposing the diaphragm. I have no idea what a good or bad diaphragm looks like, but the copper ring was not burnt, and the small wires all looked good. I did notice, however, that the positive terminal was loose. These are spring loaded metal terminals, in case anyone is curious. I tightened those up, re-seated the diaphragm (I was curious so I took it out and inspected it).

While I had the compression driver by itself I decided to run some signal through it and it sounded louder than before. I then connected it to the crossover, and I was getting good output similar to the "good" speaker. In fact, it's only about 1-2 db quieter than the other speaker in only a small section of the frequency response. I'm not sure what is causing that, but it's not really an issue during my listening tests.

There you have it, and that's the story.

If anyone else runs into an issue like this (likely very rare), start with the driver in question and go from there.

 

[MAB]

Hey there folks,

I have a pair of JBL S3900 that I recently acquired, and it seems that in one of the speakers the upper frequency crossover recently decided to malfunction recently.

The symptoms are that the mid range/treble compression driver has lower output than the other speaker. After taking apart the speaker (not fully) and testing the upper frequency crossover I found that by bypassing the crossover I got much higher output from the midrange compression driver. A visual observation of the board did not find anything out of place, no bloated caps, nothing looked like it had burn marks or poor connections, all the parts were there, and none of the solder joints were loose.

Bypassing the crossover will give higher output, especially if the drivers are padded with resistors. Have you tried swapping drivers from the good speaker, or swapping the crossover from the good speaker? It would be good to see if it is for sure the crossover. Also, do you have the image and schematic of the crossover. I can't find any online except this:

It would be first good to isolate the problem to the crossover or driver. Do you have an ammeter? It would be good to check the drivers. If you don't do you have access to electronics service? If so, they can check both drivers and crossover for gross fault. For drivers, might be useful to compare both.

If it really is the crossover, likely only one component is bad. These are straightforward to replace with like values. Sources like Parts Express will have fine selection.

Crossover Components

But first, need to find out what is broken.

If it is the driver, it will need a new diaphragm. If available from JBL, great. A good place to start is JBL and another is Speaker Exchange:

Speaker Exchange Speaker repair, replacement, recone, refoam

Speaker Exchange Speaker repair, replacement, recone, refoam | Branded speaker woofer, compression driver, crossover circuit store

reconingspeakers.com

Again, first priority is electrically determining the fault.

 

[MAB]

Thank you!

TL;DR - I resolved this issue by re-seating the diaphragm inside of the JBL 175d-3 and tightening one of the binding posts. This was likely a loose connection. Unfortunately, I didn't figure this out until after I had replaced other parts.



Reaching out to JBL, btw, was a complete waste of time. They don't sell any parts for the "consumer" speakers, and they wanted me to ship the speaker to the nearest authorized JBL repair facility to get this resolved. This would have been probably $1,000's after all was said and done (I would need to ship to Syracuse NY in my case). So if anyone else has an issue like this, don't even bother reaching out to JBL unless you have their "professional" line of products.

That being said, The Speaker Exchange has been super helpful and has gotten me all the parts I need so far.

The good news is that I've resolved this issue. What was the issue? Likely a loose connection with the diaphragm in the JBL 175Nd-3 compression driver. While I'm very glad I've resolved this issue, it hasn't been without quite a bit of effort. This effort was where the fun and aggravation stemmed from, and I often felt those feelings at the same time haha.

What did I test / do?

First I started with REW measurements using a UMIK-1 that I've had for over 5 years now. What I measured was a reduction in the mid range compression driver (JBL 175Nd-3) of about 10-20db relative to the other speaker. I took apart the speaker (including the horn assembly, which is unscrewed from inside of the speaker where the assembly connects to the wood box.

Once I had this apart, I measured the compression driver which resulted in 3.9 ohms of resistance which is within spec (3.7 DC ohms). I thought this was good news since that I meant the driver was good, and so I focused on the crossover network instead. None of the original parts were "bad" (they all measured close to tolerance), however, bypassing certain crossover parts while running a signal resulted in improved output of the driver. This is what led me to (incorrectly) thinking that crossover parts were the issue. I ended up replacing all of the caps and resistors on the circuit board with the same (or very similar) replacements. I used Solen caps and metal oxides resistors. Parts Connexion was my go-to place to get these replacement parts.

Unfortunately, replacing the crossover parts didn't do anything beneficial for me. I even swapped the crossover from the "good" speaker, and that did not improve anything either. The weird thing was, running full unfiltered signal to the compression driver resulted in strong output, so I did not know what to do next.

At this point I was out of ideas, and the only logical next step was to take a peak inside of the compression driver in question. I carefully disassembled the rear of the driver exposing the diaphragm. I have no idea what a good or bad diaphragm looks like, but the copper ring was not burnt, and the small wires all looked good. I did notice, however, that the positive terminal was loose. These are spring loaded metal terminals, in case anyone is curious. I tightened those up, re-seated the diaphragm (I was curious so I took it out and inspected it).

While I had the compression driver by itself I decided to run some signal through it and it sounded louder than before. I then connected it to the crossover, and I was getting good output similar to the "good" speaker. In fact, it's only about 1-2 db quieter than the other speaker in only a small section of the frequency response. I'm not sure what is causing that, but it's not really an issue during my listening tests.

There you have it, and that's the story.

If anyone else runs into an issue like this (likely very rare), start with the driver in question and go from there.

You posted just as I was responding!
This makes me happy! Great job. Glad Speaker Exchange helped, they are a wonderful business.

 

[Mr. Widget]

Reaching out to JBL, btw, was a complete waste of time. They don't sell any parts for the "consumer" speakers, and they wanted me to ship the speaker to the nearest authorized JBL repair facility to get this resolved. This would have been probably $1,000's after all was said and done (I would need to ship to Syracuse NY in my case). So if anyone else has an issue like this, don't even bother reaching out to JBL unless you have their "professional" line of products.

That being said, The Speaker Exchange has been super helpful and has gotten me all the parts I need so far.

Unfortunately my experience with JBL Consumer has been similar. It is a shame, because they used to have stellar service. Glad you discovered Speaker Exchange and also were able to sort out your speaker's issues.

 

[mstanley117]

This makes me happy! Great job. Glad Speaker Exchange helped, they are a wonderful business.

Unfortunately my experience with JBL Consumer has been similar. It is a shame, because they used to have stellar service. Glad you discovered Speaker Exchange and also were able to sort out your speaker's issues.

Thanks and with regards to both of you, I wouldn't be able to get as far as I have with this unexpected project if it weren't for Speaker Exchange. I'm glad they're around!