Another Parasitic Draw - Fuse 22 - JBL System

[Godzilla2y]

As I've already posted about, I have a parasitic draw on my truck of about 500mA. This is considerable, especially for its age--modern vehicles might have a parasitic draw of 50mA, and they have many more sensors than this 30-year-old SUV.

I've figured out (and am still working on) some of that parasitic draw in another thread, as seen here: Fuse 25 Parasitic Draw.

About 150mA of my parasitic draw is coming from my JBL system.

The pulled fuse that dropped my parasitic drain:

The fuse in its normal place in the Power Distribution Box (under-hood fuse panel):

Per the owner's manual and the wiring diagrams, this fuse is for the JBL System, which my EB has.

Most of the parts of the JBL system live behind the trim panel in the right rear of the truck. After slowly unplugging each item back there and re-checking the parasitic draw on the battery, I narrowed it down to the amp (maybe? I'm no wizard with audio systems) itself. Below is a picture of it as it currently sits on my desk:

To ensure it was this box and not anything downstream of it, I left it plugged in and unplugged the top of it.

This connector being unplugged did not reduce any of the parasitic drain.

I also left the amp plugged in and then unplugged the connector (on the bottom) that runs from the amp to the subwoofer.

Unplugging this connector also did not reduce the parasitic draw.

Amps are expensive. Especially when they're for a 30 year old truck. Especially when you're not trying to completely restore a 30-year-old truck.

I will not be replacing this amp (this year). Instead, I'll try to disassemble it and rectify any corrosion issues inside. I'll use this thread as a record of that attempt, so stay tuned for more.

 

[Turdle]

Check the 5v remote on signal from head unit. It may not be turning off, which would keep amp " turned on".
Another thing I can throw at ya is an amp. I just removed one, works fine. Yours for ship cost. I almost threw it away yesterday.

 

[Godzilla2y]

Check the 5v remote on signal from head unit. It may not be turning off, which would keep amp " turned on".
Another thing I can throw at ya is an amp. I just removed one, works fine. Yours for ship cost. I almost threw it away yesterday.

If that's the case (5v remote on signal), that'd be another clue pointing towards the radio. The 7.5A fuse I'm dealing with in the other thread also splices towards the radio. I'm thinking I should next unplug that head unit and see what happens to my current draw. If it drops to 0, I'll run a jumper wire one-by-one from the pins on the harness to the plug on the head unit and see which is the culprit

 

[Godzilla2y]

Check the 5v remote on signal from head unit. It may not be turning off, which would keep amp " turned on".
Another thing I can throw at ya is an amp. I just removed one, works fine. Yours for ship cost. I almost threw it away yesterday.

I meant to reply to your part about the amp, toa, but am out running around and accidentally hit *post* too quickly. If it turns out that my amp is bad, I'd love to buy your extra from you!

 

[J_C]

If the 5V signal isn't staying on, then I would suspect a leaky transistor in the amp. Is the sound system fully operational on all speaker outputs and sub?

 

[Godzilla2y]

Did some more digging for the other parasitic drain (it's not any of the relays by the rear windshield washer tank...). Got fed up with the mosquitoes and decided call it a night in the barn and instead turn to the amp on the desk in my office. Anyone know where I can find wiring diagrams for the amp? R808 looks a little toasty to me...

 

[J_C]

I know of no diagrams, but it might not be difficult to reverse engineer it enough to figure out if there's a problem.

Toasty resistor, can you tell what value it's supposed to be? Even if not, measure it with a multimeter and see if the trace it's soldered to is intact or ruined the joint or lifted the track off the PCB.

However while a circuit break at a resistor could cause a problem, it seems more likely it would interfere with audio output rather than cause extra parasitic drain. I'd first focus on the transistors on the heatsink and following the circuit backwards, looks like at least in the pic, there might be a smaller transistor to the right, biasing it? I could be wrong.

Anyway, you might also see if the channel that resistor and the transistors are on, is mirrored by another subcircuit for one of the other channels, then you can not only measure the corresponding resistor on that other channel but also, take measurements at several locations and compare one channel to another to see where the readings look off.

 

[Godzilla2y]

I know of no diagrams, but it might not be difficult to reverse engineer it enough to figure out if there's a problem.

Toasty resistor, can you tell what value it's supposed to be? Even if not, measure it with a multimeter and see if the trace it's soldered to is intact or ruined the joint or lifted the track off the PCB.

However while a circuit break at a resistor could cause a problem, it seems more likely it would interfere with audio output rather than cause extra parasitic drain. I'd first focus on the transistors on the heatsink and following the circuit backwards, looks like at least in the pic, there might be a smaller transistor to the right, biasing it? I could be wrong.

Anyway, you might also see if the channel that resistor and the transistors are on, is mirrored by another subcircuit for one of the other channels, then you can not only measure the corresponding resistor on that other channel but also, take measurements at several locations and compare one channel to another to see where the readings look off.

I got in touch with Turdle about getting his extra amp. I worry the next one could blow if I plug it right in, so I'd like to do some more digging on this one, too. I'll work on further disassembling it tonight and check out the other side of the board. I have a soldering station, so I'll be able to pull the blown resistor off the board.

In the meantime, while I'm working on the other drains, how would I go about checking if that 5v signal is stuck on?

 

[Turdle]

Find it with radio on, turn off radio. Should drop from 5 v to 0

Found a box , I'll head to po asap for a ship price.

 

[Godzilla2y]

Find it with radio on, turn off radio. Should drop from 5 v to 0

Found a box , I'll head to po asap for a ship price.

Thanks!

Where do I stick the DMM probes, though?

This may be difficult, either way--the power on/off function of the radio volume knob doesn't work anymore. It no longer physically clicks into place to stay off.

 

[Turdle]

That could be an issue. Although head unit power should go away with key off also. Check that the 5 v with key on, goes to 0 with key off.

One red probe on 5 v remote on signal line, black probe to ground

 

[Godzilla2y]

That could be an issue. Although head unit power should go away with key off also. Check that the 5 v with key on, goes to 0 with key off.

One red probe on 5 v remote on signal line, black probe to ground

This plug?

 

[J_C]

I got in touch with Turdle about getting his extra amp. I worry the next one could blow if I plug it right in, so I'd like to do some more digging on this one, too. I'll work on further disassembling it tonight and check out the other side of the board. I have a soldering station, so I'll be able to pull the blown resistor off the board.

One thing you could do is a resistance check on the speaker wires coming out of it to make sure those aren't shorting out. +/- for each channel should read about what the speaker itself is rated for, single-digit ohms. There should be a wiring diagram showing those speaker wires in the 2nd gen wiring diagrams linked in my sig below, but note there are at least 4 different radio combos, with at least a couple of them having an amp.

If they aren't shorted, then the amp probably just died of old age. Sometimes transistors just get leaky, or capacitors dry out.

 

[Godzilla2y]

One thing you could do is a resistance check on the speaker wires coming out of it to make sure those aren't shorting out. +/- for each channel should read about what the speaker itself is rated for, single-digit ohms. There should be a wiring diagram showing those speaker wires in the 2nd gen wiring diagrams linked in my sig below, but note there are at least 4 different radio combos, with at least a couple of them having an amp.

If they aren't shorted, then the amp probably just died of old age. Sometimes transistors just get leaky, or capacitors dry out.

Wouldn't unplugging all the outputs from the amp (and not seeing a change in current draw) have eliminated that possibility?

 

[J_C]

Wouldn't unplugging all the outputs from the amp (and not seeing a change in current draw) have eliminated that possibility?

I'm stating that a short could have damaged a transistor in the amp, so it became leaky or shorted, even without the speakers still connected. It is just something I would check before hooking another amp up, or finding and fixing the fault on that one, IF/assuming it has the fault.

On a side note, I'm a little confused by your amp, due to seeing that toroidal inductor on it. The typical amp board pics I've seen, more closely resemble this one with no inductor, at least not the larger toroidal type:

Fixing Jeremy’s Ford Mach 460 Bass Amplifier « Keith's Electronics Blog

 

[Godzilla2y]

Took the amp apart while I waited on some emails at work. I will not be able to identify this resistor from its color markings.

It made a pretty nasty burn on the reverse side, too.

While checking the underside of the board, I also found a second spot that looked a little scorch-y:

And the front of it, which doesn't show much evidence of heat:

According to the markings and some fast google, this may be.. a high-frequency ceramic capacitor?

 

[J_C]

That 1101CB (?) looks like it may be an NPN transistor, definitely not a capacitor. NPN because some motorola and RCA part #s with 1101 in them are NPN.

The resistor solder joint does look damaged and in need of repair. I can't tell from the pics if the other joints are acceptable or not. I highly doubt that just replacing the resistor and a good solder joint to it, is going to fix this. Looks more like another fault put too much current through it.

It is near impossible to get a good idea of this circuit with just small portions of the board showing at a time. A hi-res 90' top-down pic of the whole board would better show the topology.

 

[Godzilla2y]

That 1101CB (?) looks like it may be an NPN transistor, definitely not a capacitor. NPN because some motorola and RCA part #s with 1101 in them are NPN.

The resistor solder joint does look damaged and in need of repair. I can't tell from the pics if the other joints are acceptable or not. I highly doubt that just replacing the resistor and a good solder joint to it, is going to fix this. Looks more like another fault put too much current through it.

It is near impossible to get a good idea of this circuit with just small portions of the board showing at a time. A hi-res 90' top-down pic of the whole board would better show the topology.

Ask and ye shall receive

 

[Turdle]

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

 

[Godzilla2y]

Unplugged the head unit to check for the rest of the drain, which didn't change anything. Once I plug it back in, I'll test the voltage at the plug that goes into the amp (presumably from the head unit).