Cougar amp with blown caps, diode split and transformer trying to desolder itself

[Mote]

I have a lot of 4 broken Cougar amplifiers.

Worst of them suffers from symptoms described in the title, attached some photos of the damage.
I am a bit scared to try to do anything about it, I can replace the blown components but how can I be sure they wont explode in my face.

What could be the cause for something like this to happen, user mixed GND and +?

Is it ok that the inductor is touching transformer?


2nd amp

On another amp exactly like this the same inductor is touching fuse holders pins that is also something to worry about?

That amp doesnt make a beep, neither power or protection light comes on. Power supply chip has 12V on leg 12 but most of the other pins are 0V.

Blown power supply chip?

3rd amp

Had protection and power LED lighting up. Problem was with transformer windings touching, twisted the transformer a bit and got the amp to power up and produce audio but it had a small current draw all the time. Desoldered one leg of transformer added insulation, soldered it back. Then amp drew maximum amount of current 12V current limiting lamp allowed it to. It had DC 8V on speaker terminals. Then desoldered another leg of transformer and added insulation to that as well. Now current draw is much smaller, amp pushes speaker cone out a bit but plays music nevertheless.

I will repeat the procedure with other transformer legs which are too close to windings?

4th amp

Had blown outputs, emitter resistors and a couple of traces were burnt. Fixed traces, borrowed transistors from another amp and that one works well now.

[AKHeathen]

well, where to start?...... first, let me say, i'm not a pro, just hobbyist, but where i would go with them.......
amp1:
up here in the great white north, i see this very common, in both new, and old amps, so it's not really a deterioration factor, but the electrolytic caps are like car batteries (cliche', i know) and can freeze/swell, and explode in sub-zero, or near 0*f. first thing i would do, is remove all electrolyticc caps, including rail supply, and test individually. if it is swolen, replace, even if tests ok. check the ps fets, and even outputs for good measure. once you order your parts, test first with the rectifier diodes removed, to ensure proper ps operation, then re-install the diodes and test for output voltage before hooking a load. no dc voltage @ idle, and proper ac voltage on a tone. it is also a possibility of the damage happening from reverse connection, but likely just bad/froze caps, and/or an result of a drained battery in the vehicle and jump-start damage. also, regarding the transformer, could be current draw through a dry connection, either pre-existing during operation, or a result of a bad cap/transistor/short on the output, or external, either way, there is/was dry connection(s) that needs fixed

amp2: ? i would personally ask for help from someone like perry when it comes to the driver circuitry, but i would immagine there should be power to more then one pin, so it might be in the remote circuit, or power supply, to the driver.

amp3:
once you get the transformer squared, but before powering up, test the output transistors, and their drivers. sounds like one, or more of them are blown (short), and, if you cannot find what is, remove them before powering up, and make sure they are not getting fed continuous power from the drivers.
amp4:
well, good that it is fixed (for now) but a good idea to make sure the whole bank is matched, either by all from the same doner amp bank, or order new (10+ at once, to ensure match) or they may not all be working the same. all the resistors in the bank should be new, as well.

[Perry Babin]

It's very confusing to have multiple repairs going in one thread. Start new threads for the other amps.

It's not good for the inductor to touch anything that could cause the insulation to wear through and short to anything conductive.

The amp was likely connected with reverse polarity if the reverse protection diode failed.

Let's deal with amp 3 from this point on in this thread.

Do both channels have equal DC?

[Mote]

It has 4 channels and DC is equal on all of the channels.

[Perry Babin]

How much DC is there?

[Mote]

After desoldering, insulating first leg, it had 8V on speaker terminals
After desoldering and insulating second leg it had 2.4V DC on speaker terminals.
Cone gets pushed out a bit but all channels produce audio at high volume, bass is distorted because the cone is not in the center but higher frequencies sound OK.

[Perry Babin]

What is the resistance from the RCA shields to the non-bridging speaker terminals (no RCAs plugged in)?

What's the positive and negative rail voltage on the center legs of the output transistors?

What's the DC voltage on the power supply pins of all of the op-amps (all should be the same)?

For the voltage readings above, measure with no RCAs plugged in. Measure with two ground references. First measure with the black probe on the main amp ground. Then measure with the black probe on one of the non-bridging speaker terminals.

[Mote]

Resistance between RCA shield and non-bridging speaker terminals starts from 0 and starts to climb endlessly. On OK amp we would like to see 0 ohms?

Amp Ground:
Rail voltage on center legs of outputs: 22V and -22V
Voltage on power supply pins of all the opamps: -15.3 and 13.7

Non-bridging terminal
Rail voltage on center legs of outputs: 22.1V and -22.1V
Voltage on power supply pins of all the opamps: -15.4 and 13.8

DC between bridging terminal and ground: -8,7V

[Perry Babin]

On amps that use secondary ground isolation to prevent ground loops, yes, you'd want to find 0 ohms from the RCA shields to the non-bridging speaker terminals.

Look for an open trace on the RCA shield ground. It could be a bad solder connection on the RCA jack or an open trace on the board.

[Mote]

As always Perry Babin is 100% right. It was a burnt trace. Sorry for wasting your time. The fourth amp which I managed to repair without asking any advice had a burnt trace on the exact same spot. So I knew what to expect and still didnt find it.

Now the amp has 0.00V of DC on speaker terminals.
Produced audio and does not draw current.