Troubleshooting help...

18 dcsb TRD with JBL. I have a Rockford Fosgate 4 ch amp driving Kicker front components and rear speakers. I also have the PacAmp Pro

$329 AP4TY12 PAC R AP4-TY12 Amppro 4 Amp Interface (Select 2012-2018 Toyota(R) & Lexus(R) Vehicles with Jbl(R) or Premium Amplified Sound Systems), 1 Pack

AP4TY12 interface. OEM head unit. Everything has been fine for 2 years. Last week suddenly I lose sound from all speakers other than front left. At the same time the volume of front left is higher and a high frequency hiss is heard. Even when i turn off the head unit, the hiss is still heard. This issue is sporatic. It will happen and then go back to normal. I immediately suspected the AmPro module. Crutchfield sent me a replacement. I swapped it out but the issue persists. So...other than replacing the amp how can i troubleshoot this? Any ideas? How can I measure the output of the amp?

 

A digital multi-meter from harbor freight for $10

set it to AC volts

 

A multimeter to measure the speaker terminal output? What AC Volt output value should I expect as normal? I guess I was thinking it was measured in Watts and not Volts.

 

Seeing 10+ volts would tell you the amp is putting out plenty of power

 

Factory radio stays clean till like 7volts I think

 

Thanks Destin! Ill check this tomorrow and report back.

 

Check this out.. enter the amp watts and speaker ohms and it'll give you the rest.

https://testguy.net/content/266-Ohm-s-Law-Watt-s-Law-Cheat-Sheet

 

So I picked up a cheap Kolbalt MM and I get 0.00v. I had a sine wave running from my phone at 1kHz. What am I doing wrong? The MM shows roughly 13 volts when I check the amp power terminals as expected. 0.00v when i check any of the speaker output terminals.

 

Audio is AC volts. You’re set to DC

 

You also want to disconnect your speakers when doing that, because pumping sine waves into them will blow them faster than anything else (and hurt your ears)

 

Does this look right? Consistent across all 4 channels.

 

No, not if there “should” be audio playing.

turn off the truck, go to the battery, and pull the amp fuse.

count to 30, and put it back.

try again

 

Yes there was sound. No issue when I took the measurement. Ill pull the fuse and remeasure.

 

Im about to lose my $h*t!! So the sound issue happened and I connected the MM. 0.0v on all channels. I disconnected power to amp, reconnected after 40 sec and the issue remains. 0.0v. Do you think it makes sense to replace the amp? If the issue still remains then it has to be the OEM HU.

 

When you installed the amp, did you cut and splice them factory wiring? Or build a t-harness behind the factory radio

 

No splicing with the PacAMP, plug and play. I did however splice into the factory speaker wires bundled behind the rear passenger seat. I think I'm going to "borrow" an amp from local big box retailer tomorrow to rule out the amp.

 

I would just hook back up all the wiring back by the amp to factory and see. If you used the APH harness, your JBL amp should still be ready to go.

 

That's a way to rule out the HU. I soldered all 8 speakers leads though...that would be PITA to revert back to factory just to rule out the HU. I believe I will replace the amp. 10 minute swap.

 

Oh so you cut and spliced the JBL wiring? Bummer

in that case, an amp swap will be the easiest thing to check