Broken Car Amp

[Jaderman]

I have a Rockwood Detanator 400W car amp that I got at a yardsale (for $3 =O) and it doesn't work at all. Is there any part that usually breaks on a amp? Or is it always unpredictable? I opened it up and there is nothing unusual on it. Are there any guidelines I can follow to troubleshoot the problem?

I wanted to use it for my drum set since I didn't have a speaker system yet and then for my future car.
Thanks

 

[shrtrnd]

Typically the output amplifier section goes.
First check the fuses (power input to the amp), then see if there are fuses to the
output (speakers). (could be internal to amp, or in-line with the speaker wires).
If the fuses are ok, usually the output amplifier transistors are blown.
(And you're right, it could be something else, but that's where to start).

 

[Jaderman]

There is only one fuse on the outside that is good. There is no other fuse so it might be the transistors. Do you know which ones might be the output amp transistors? I can take a picture of the board if that makes it easier for you to show me. And how can I test a transistor to see if it's good?

 

[shrtrnd]

If you can submit a picture of the board, you'll get a LOT of responses from guys on
this website with advice.
In car amps these days, the output amps are typically big multipinned modules that
will be bolted to a heat sink to dissipate the power.
My advice is to add the picture to your post here, and maybe somebody who knows
your exact amp can help. In any event, you'll get quite a few other people responding.
It can be fixed. It's just a matter of how much the part or parts might cost.

 

[Jaderman]

Here is the pic of the amp. I wrote info about it in the description.

And while you're there, you can peek at my other pics if you wish. =)

 

[shrtrnd]

You've got TO-220 Pkg power devices bolted to both sides of the chassis (sandwiched
by another metal plate to help dissipate heat).
There are 3 leads on each one of these devices.
Use an ohm-meter (amp NOT powered), and check continuity between the 3-pins on
each device. You're probably going to find shorts or opens. Shorts are definately bad.
Sometimes high resistance (similar to an open circuit) are found that are normal
depending on the device.
The part number should be on the front of each device. If you get questionable resistance
readings on a device, compare it to equivalent part number on the other devices.
There might be something else wrong, but you've most probably got bad TO-220 package
devices. They're probably voltage regulators and transistors, ...you can find data sheets
on-line for the devices if you're interested.

 

[Jaderman]

So I took the metal plates off of the eight transistors and the top and bottom two pairs to the right are TIP3055(which is NPN) and the other transistors next to it are TIP2955(the same as TIP3055 just PNP). Is there a possibility that ALL four TIP3055s are broken? Cause I tested them and there was continuity from the emitter to the base instead of continuity from the base to the emitter. (I did desolder the base of each before I tested it.)

 

[Jaderman]

Here is a pic of the transistors that I am talking about.

 

[shrtrnd]

The TIP2955 & TIP3055 is complementary (one PNP, other NPN).
I pulled a TIP3055 out of my parts box.
I read:
Base to Collector 1.86M Ohms one way, virtual open the other way
Base to Emitter 1.94M Ohms one way, virtual open the other way (back to back reads)
(It's a TO-218 pkg by the way, not TO-220)
The TIP2955 would read the exact opposite.
All other back to back readings are virtual open (Resistance too high to read)
Transistor characteristics vary depending on the device.
If you read what I did on the TIP3055, the device is probably ok.
After checking these readings, let us know what you've got.