nakamichi amp issues

It's been a long time since I posted anything on here, but when you have an issue where else can you turn?

My background:  Running a Factory Toyota HU in my Tacoma with Line out  (not sure of term) converters to RCA's.  This connects to my Nakamichi PA-2100 amp.  I've had no issues for 2 years but this last (Canadian) winter I've had issues with the amp going into Protection mode.  Typically when the truck has been sitting outside I can't turn the volume up past 35.  After it warms up, it cuts out past 42.  Now when it sits overnight underground at my apartment I can't turn it up past 48.  Seems like the cold is doing something.

Recently I have done some testing by disconnecting all the speaker leads from the amp and it goes into protection mode around those volumes which leads me to believe it's between the HU and AMP, not from the amp to speakers.  What makes it even weird is that when I am in the underground and have it on the radio with just static playing I can turn it up as loud as the HU will go without problems?

Last night I hooked up a Multimeter to the B+ and Ground leads of the amp.  Without the truck running it was 12.5 consistantly and when it goes into protection with the volume increased it stayed 12.5.  Only when it came out of protection mode did the voltage drop to 11.3 then returned to 12.5.

One last item I should point out is that the amp is under the folding jump seat and close to my daughters feet.  The potential for water is increased.  However I would like to know what else I could try to troubleshoot before having to open the amp up.

I was thinking of hooking my ipod using a 3.5mm headphone to rca jack converter and removing the HU and line out converters.

Just to clairfy this, I will use the Ipod connected directly 1 channel at a time and remove the HU and rca's from the equation.  Does this sound like a feasable test considering I don't have duplicate equipment or bench area to test the amp?

Yes the I-Pod is a good idea, chances are you will notice that only one channel is making the amp go into protection. You can just drive one channel at a time and see if only one channel makes it go into protect. If only one channel is causing the amp to go into protect, chances are it has bad solder joints on the emitter resistors on that channel.

Ampguts has no pictures of that particular amp.  If you could take a few pictures of the inside of the amp, I can probably help you get it working again.

*Update*

I tried each channel individually from the HU and it cut out when the volume was raised to different levels.  I then tried connecting just the Ipod and it didn't cut out even at Max volume.  Suspecting that the Ipod is probably less power I turned the gain up just a little and it cut out, on each channel.

I guess it's time to open it up and see if there's anything noticable.

Ok, first let me say I was wrong on the model, it's the PA 4100 that I have, not the 2100.

Next, I was about to replace it with a cheap used $40 amp I picked up when I thought about checking the fuses on the amp.  They all looked good, but from my issue it seemed possible that there was a crack or something not right when cold.  This amp had 4 fuses and would work even if one isn't plugged in.  I picked up a 5 pack and so far after replacing it (10 min test) I had no issues at the volumes I originally posted.  I then proceeded to turn it up louder then I normally have it and it cut out, but I satisfied with the volume I can now play it at.

I will post back if I notice anything else because this may help someone else in the future.

So, this is an old post I actually came across from Google.

My basic troubleshooting steps. 

1. Confirmed that the amp goes into protection without speakers connected.

2. Confirmed my RCA's work on a friends amp.  HU, Lineout converters worked without cutting out his amps.

3. Replaced the amp with a used one I picked up and still had same issue.

4. Replaced the Ground wire (4 Awg) with anoher 4 Awg.  Power wire is only 8 Awg from Distribution block.

5. Used Multimeter to determine that voltage from Battery is the same as Amp leads.

Next steps I'm going to take.

Move the ground wire to another location. (where my other amp is grounded.  Failing that, have my amp bench tested or look at replacing Amp Wiring kit.