Contour Enthusiasts Group Archives Forums Modifications Audio amp is acting retarded

My Pioneer amp that I am using to run a JL 12 seems to just shut off and turn back on at will. Now I don't mean power off I just mean stop producing wattage. And it seems like it will come back when I hit a bump or take a hard turn. My first initial thought was loose ground but everything is secure. The amp never loses power, it just like quits.

So...the other day my amp cought me on a bad day and it stopped on me so I popped the trunk and just punched the damn thing. Whata ya know it starts up again. So whats the deal? Think maybe its a loose wire inside the amp? If so what would I look for. I dont want to rip it apart and just poke around at stuff.

Thanks

Take the cover off it and look... maybe it's something dumb like the Pioneer in my closet... the power input terminal is loose on the circuit board.

I guess I should specify what cover... I took this Pioneer apart, but I didn't want to mess with the heat transfer compound/cement that is holding the heat sink and related parts together. All I removed was the bottom cover and immediately saw my problem.

I had a loose connection on my battery do that. Also, bad solder inside the amp is very possible, if the wires are secure on the connectors and it is still misbehaving.

Yup you have a bad soilder joint on the circuit board.

I have run my own electronic repair shop on the side and have been doing repair for about 11years.

If you like to ship the amp to me I will fix it for nothing. I have everything to trouble shoot audio circuits.

If you do want to do it yourself. Get a plastic stick or something small that doesn't conduct. Take the cover off and with power on tap around inside.
When you start getting close to the loose part (cap, transistor, resistor, IC, coil.) it will cut out and back on with the taping. With the way they wave soilder the pc boards these day bad soilder joints r very common in everything. After you get close mark the area with a marker, tare the rest down (mostlikely you will have to remove the transistors from the heatsink which is the casing) you will need heatsink compound (its that white stuff you see inside the amp, radioshack has it still I think) then use soilder iron to repair the connection.

If you take a pic of the board, I can break the sections down for you and give you some ideas where you might want to start looking. And watch those caps, they can store 50-100 volts even after you unplug the unit.

great info jd28:

I follow you up to this point but may need a little more clarification from this point on:

"After you get close mark the area with a marker, tare the rest down (mostlikely you will have to remove the transistors from the heatsink which is the casing) you will need heatsink compound (its that white stuff you see inside the amp, radioshack has it still I think) then use soilder iron to repair the connection."

What do you mean tare the rest down and removing the transistors from the heatsink? Also what do I need to do w the heatsink compound?


"If you take a pic of the board, I can break the sections down for you and give you some ideas where you might want to start looking. And watch those caps, they can store 50-100 volts even after you unplug the unit. "


I have a digi-cam I can take pics. This might be the best help. Can I e-mail you the pics?

I have a bad amp here too, they all usally come apart about the same. Percocet messing me up, looking at post I started getting lost myself lol. I smashed the crap out of my hand working on the contour, and lost almost the top half of my thumb Send me some pics email. Also I'm going to snap some pics to post here.

jman2343@hotmail.com

Ok here is the start of it.

Flip the amp upside down and take the cover off.




Here is the inside.




Most amps will have somewhat the same setup, the donut looking thing is the transformer so you know that area is the powersupply section.
There they make DC into AC pass it over the transformer stepping it up to a higher AC then converting it back into DC to supply 24-105volts
for the AMP section.

CH1 and CH2 would be LEFT and RIGHT, they r 2 seprate circuits. So if you had just the left cutting in and out you would start tapping in either CH1 or CH2
to see which is more sensitive to the tapping.

The input section and signal preamp section. If your loosing sound on both channels at the same time this would be a good area to start.



As you start getting closer to the component that is loose, it will start acting up more with the tapping. Start lightly prying on components.



After you think your in the general area of the problem, it's now time to disconnect everything and strip the rest down to gain access to the back side of the circuit board.

Will be back with more.

I forgot to say the tapping test for broken connections is done underpower. Best to do this installed in car, unless you have a benchtop power supply.

Ok To gain access to the soilder connections, will take some work. The bigger the amp the more you have to unscrew. Move slow and carefully, you should be fine.

Removing board is done under no power



remove just the screws holding the end plates to case/shell/ampbody whatever you like to call it.

Next remove all screws holding clamps for transistors and screws holding circuit board to case.







This amp uses thermal pads, usally you can run something thin under the leads of the transistor and rock them off the pad with out damage to the transistors or thermal pad. The pad can be reused aslong as there is no damage. They usally stay stuck on the case. There is some transistors on this board that use just thermal paste. I will go into that later.



After all that you should be able to get the board out, by lifting up on the side plates.



Now to look closer at the area or part you found bad. You should be able to see the bad connection. This helps.



more to come. Questions input welcomed.

awesome. It all sounds good so far. I will have some spare time this weekend to take a look at it. Hopefully I can put your notes to use and figure this thing out.

I'll let you know what I find.