Another Parasitic Draw - Fuse 22 - JBL System

[Godzilla2y]

R 807, upper right near other output transistor also got hot. Those outputs are shorted , my bet.

Shorted outputs... Which means I should check the connections for the rear speakers?

 

[J_C]

From what I can make out, I would replace each of the 3 transistors in turn, replace 1, plug back in and measure for parasitic draw, replace 2 plug back in and measure, then #3. The trick would be finding modern equivalents or at least known correct datasheets for them to do that.

R (R807) on this pic is "probably" the same resistance value of the one damaged, R808?. These might inherently run hot, but I'd replace R808 with same value as R807, and if the trace is lifted, tack it down with superglue or add a piece of jumper wire (solid core ~22 ga. or so, whatever really), and reflow that solder joint. It wouldn't hurt to choose a higher wattage resistor rating, is what I'd do, like if they are 1/4W rated, get a 1W replacement.

 

[Godzilla2y]

R 807, upper right near other output transistor also got hot. Those outputs are shorted , my bet.

Woah-ho! Took a closer look at the components you mentioned, and check these out! R807 and Q805, specifically.

Something definitely did something it wasn't supposed to.

So. How do I check the outputs? Unplug each of the speakers and see if that drops my parasitic drain?

 

[J_C]

Why would you check the outputs at this point? You need to see if your speakers/wire is shorting out. If it is, fix that. Once that is right, you either drop in a replacement amp or repair the damage that you see and retest.

 

[Godzilla2y]

Why would you check the outputs at this point? You need to see if your speakers/wire is shorting out. If it is, fix that. Once that is right, you either drop in a replacement amp or repair the damage that you see and retest.

I assumed "outputs" meant all the things down the line, like all the speakers. I'm now realizing that's not what it meant.

 

[Godzilla2y]

I posted this in the other thread last night, but it's relevant here, too:

I got a few things plugged back together and tried testing a couple odds and ends to see if everything worked as well I remembered (everything did not, in fact, work as well as I thought).

The driver's door lock button doesn't work, but the unlock button does.

I remembered from many forum posts here and many youtube videos that the wires in the driver's door boot can get brittle and break. Took that all apart. Wires look brand new everywhere I can see them. Checked the parasitic draw while this connection was unplugged, still 110mA.

Then I remembered a forum post or video from I can't remember when to next check the wires under the trim by the back driver door.

Checked the harness at the rear of the back driver's side seat, which looks fine. Didn't want to get into tearing apart that part of the trim tonight, even though the whole back is currently opened up.

Then I remembered some more:

• A long, long time ago, this thing went through a flood. I don't know how high the water got inside, but I'm guessing it got inside at least a little.
• In 2012 (several years after the flood), I was trying to get this thing running so I could drive it to and from school. At that time, the interior lights would not shut off. 2012-me solved this by cutting the wire for the back driver's side door. (Thanks, kid.)
• Other thread is looking like there is a short in the stereo outputs somewhere...

I think I really need to tear up the trim by that back driver's side door. I think I'll find the source of a whole bunch of issues somewhere in there.

Don't the lines for the rear speakers also run through this harness?

If so, I wonder if I'll find broken or corroded wires for the locks, the speakers, and the door ajar switch (and maybe more!) all in one place. At this point, a man can hope.

 

[Turdle]

The door ajar aka dome light switch is located inside the door latch. It's common for those switches to remain open, with door closed. Sometimes that switch can be cleaned.

 

[J_C]

I assumed "outputs" meant all the things down the line, like all the speakers. I'm now realizing that's not what it meant.

My reply was a little premature. Testing the outputs of the amp itself is not a bad idea, with stereo off, see if any AC (or even DC) voltage is on the outputs without the speakers connected, and there should be none, then with the stereo on (playing audio), there should be AC output, but very minimal DC, like a few tens of mV DCV at most, with absolute 0V DC being the ideal. Again the speakers don't need to be hooked up to measure this. I would just wait till after any repairs are made to do it.

 

[Godzilla2y]

Printed out all the wiring diagrams for the radio.

Ripped out the back seats and half the rear interior.

First, a correction: it was my subwoofer amplifier that was causing a drain, not the main amp (sorry, Turdle--I can send the amp back to you, if you want).

Next, some resistances.

Plugging the probes into the sub's plug, I get about 5.8 Ohms.

7.2 ohms each for the rear speakers from the Remote Chassis Unit Plug (did I do this right? I've included the wiring diagrams and circled the relevant areas that led me to where to test)

For the two front speakers, I get... open circuit.

 

[Godzilla2y]

Feel like I'm on a wild goose chase here.

To save myself some sanity, a question: could turning the volume up too high blow the bits in the subwoofer amp and cause this parasitic drain?

 

[J_C]

Volume too high can blow the amp, would happen one channel (subwoofer being treated as just another channel for this) at a time since each has its own output subcircuit. It's not what I'd call a common thing to happen, but considering their age, the heatsinking may be compromised at this point especially if using thermal compound, it may have dried up and left behind islands of zinc oxide that don't conduct heat well.

You can hook up power and play audio and see if that output produces AC voltage and minimal mV DC voltage, same as the other channels. If it does this, it has output even if it is distorted which you could check next by hooking speakers back up, after checking all channels to make sure none have a problem to fix before subjecting speakers to that... because a lot of DC voltage can blow the speaker(s), a lot being even a mere 1V DC.

Assuming you measured correctly, I would check the front speakers at the speakers to see if they are blown. Measure directly at the speaker, and if it measures good, single digit ohms, then measure for resistance between the connector to each and the rear connector to the amp where you already measured, in case there is a fault in the wiring.

 

[J_C]

I didn't specifically state it, but you know that you shouldn't bother hooking the pictured amp back up before replacing Q805, right?

I mean it is safe enough to hook the amp back up to test other channels if the speakers aren't connected, but that transistor is toast and no hope of salvaging the amp without replacing it.

 

[Godzilla2y]

I didn't specifically state it, but you know that you shouldn't bother hooking the pictured amp back up before replacing Q805, right?

I mean it is safe enough to hook the amp back up to test other channels if the speakers aren't connected, but that transistor is toast and no hope of salvaging the amp without replacing it.

Oh, yeah. Definitely know.

So... nothing new has changed in this truck since the last time I drove it (just a few months ago).

And, last time I drove it, I don't remember any of the speakers not working.

Is there any harm in turning the radio on (at a low volume) to check if any of them don't have sound?

 

[J_C]

Probably not harmful, but if it is producing more than a tiny bit of DC voltage on the output, that can blow the speaker on that output.

 

[Godzilla2y]

Probably not harmful, but if it is producing more than a tiny bit of DC voltage on the output, that can blow the speaker on that output.

I tried it last night. All my speakers work! Subwoofer amp is still unplugged

 

[Turdle]

Subwoofer amp should be arriving soon.

 

[Godzilla2y]

Used a break at work to print off all the connector diagrams and locations for these two front speakers. Got the connector for the driver's door unplugged.

Resistance from the female connector to the rear control panel is about 130 ohms.

Another open circuit on the pins to the front speaker, but it's very difficult to get my probes up in there. The speaker works, so I know it's not blown.

 

[J_C]

I'm not familiar with the connectors themselves but if that is measured on the correct contacts, 130 ohms is far too high, should be single digit ohms. I'd wonder if the wire is frayed in the door hinge boot like can happen with the power wires for the window and door locks.

 

[Godzilla2y]

Just realized my readings may be off. These terminals are all coated in an old green grease, and I saw in checking the terminals for connector 240 that my probes couldn't fit into the female pins properly.

Connector 240 (pictured below, that I'm pointing to with my thumb) connects the front speakers and the backseat radio controls to the rear audio box (that lives next to the subwoofer amp, allll the way in the back:

Connector 240, according to the wiring diagrams, is located on "the right side of the instrument panel, by the cowl grommet". Also known as behind right trim panel in the front passenger footwell.

I had to run in for dinner. I made a few jumper wires right before that to get getter penetration into the connectors. I'll start by testing the front speakers again with them once I get back to it.

 

[Godzilla2y]

I can not for the life of me get an accurate reading for these speakers. If there was a short, or if there was something wrong, wouldn't the speakers not work when the radio is powered?

I suspect my open circuit issues (and even my high resistance issues) are caused by a poor connection between the probes and the connections for the different audio components.

I decided to go back to square one.

I know that the pulling the JBL fuse dropped the parasitic drain on the battery.

I know that unplugging the power from the subwoofer amp dropped the parasitic drain the same amount.

I know that unplugging the fuse after unplugging that subwoofer amp had no impact on the parasitic drain.

I know all the speakers worked before the amp died (at some point).

I know that all the speakers work when provided sound from the radio, with the amp unplugged.

So.

I returned to the subwoofer amp to check the plugs that run to and from it.

The subwoofer tests fine, with a reasonable resistance.

There are no shorts between any of the other pins in any of the other cables that plug into that amp.

I now heavily suspect the subwoofer amp failure was caused by user error (younger me, who liked to loudly play bass-heavy music). I should not have abused 30-year-old electronics.

Unless anyone has any urgent warnings, I'm going to consider this issue resolved.