4 Channel Car Amp not outputting

[partyanimallighting]

Hi guys, novice me again. I'm taking a gander at a 4 channel car power amp. It was given to me because one of the RCA line inputs was broken so I figured I could repair it. Changing out the RCA input wasn't too much of a problem. However, even though the amp powers up fine, I am not getting any output. Sooooo.....I opened it up again and did some precursory voltage testing. There is a bank of smaller transistors on either side of the amplifier and I checked voltage on each pin on each of these smaller transistors and I'm getting Pin1 0VDC, Pin2 12VDC, Pin3 0VDC on the first 6 on each side. On the last two, I'm getting Pin1 -0.06VDC, Pin2 0.5VDC, Pin3 -0.01VDC. Any ideas as to where to proceed from here? I AM NOT A TECHNICIAN! I am technically inclined and love to poke around and, because of all the help from you wizards, I have repaired a lot of stuff in the past. Here are a couple pix....

 

[kellys_eye]

You might by now realise that we like to know the make and model numbers - perhaps a schematic and/or link to the manuals? It's difficult to diagnose a fault from 'pictures' and randomly taken measurements.

Is there a 'mute' circuit for the amp?

 

[partyanimallighting]

Hi kellys_eye, sorry about that. I've had problems resolved before in this forum and I do know that a schematic is the most desirable thing that I can post but I have searched online into the black depths of the Internet and cannot find a manual or schematic. I did find out that the brand is DS18 and the model number is GEN2400.4 but I cannot get any further information, not even a user or installation manual so all I have is the pictures and randomly taken measurements for now until I get some further guidance. As for the mute circuit, there's no switch that I can see. I hope you can understand my predicament and you are still willing to assist.

 

[Bluejets]

Note that for any future work, using soldering gear like you have in the photo might be one of your problems, if not now, then further down the track.

 

[partyanimallighting]

LOL!!! Noted Bluejets!!! I'm in the process of ordering one of those hot air soldering stations with temperature control, different nozzles etc.. Good idea? Not to stray for the existing post.....

 

[Bluejets]

Thoughts were more along the line of anti-static actually.

 

[partyanimallighting]

Anyone willing to offer some assistance here??? Please????

 

[kellys_eye]

Anyone willing to offer some assistance here??? Please????

Is there a 'mute' circuit for the amp?

You might by now realise that we like to know the make and model numbers - perhaps a schematic and/or link to the manuals?

I have searched online into the black depths of the Internet and cannot find a manual or schematic. I did find out that the brand is DS18 and the model number is GEN2400.4 but I cannot get any further information

Your Google-fu is cr@p....

http://www.ds18.com/_p/prd1/2059219655/product/gen2400.4



As little as I found is more than you provided and at least gives us something to go with:

1. Note the 'remote' connection on the power input block - this switches the main power on/off. Have you done so?
2. Note the 'CAT5-like' remote socket on the other end. Do you have the control head? How else would you control it?
3. Note the 100 Amp input fuse - do you have a power supply capable of delivering such current? Even switch-on surge could require 10's of amps.
4. Note that the system has protection for all sorts of mis-connection, including speakers? Do you have any suitable speakers connected?
5. Have you checked the internal power supply lines?

 

[partyanimallighting]

Hi kellys_eye. I found basically the same web page and no more, no user manual, no schematic, just that basic info.
1. I connected the 'remote' to the 12VDC feed and the unit does power up.
2. No remote control head. Got the amp as is. It's powering up fine and I've run a signal feed into it, all relevant gains are up but no output.
3. I'm using a 30A 12VDC power supply for testing.
4. A pair of 8Ω house speakers for testing.
5. There are no real power supply lines as such. The 12VDC goes from the connector terminal, down the gold plated rods at top right in the photo directly to the PC board.
Sounds adequate?

 

[kellys_eye]

1. Good - measure the input supply current. Are any internal LEDs lit?
2. Bummer - I suspect you'll need the remote to get the unit to power up. The 'remote' connection on the power input switches the main supply on/off but I reckon there'll be a similar signal to switch the audio on/off. You'd normally connect an auxiliary audio output from your usual car stereo to the audio input of the big amplifier and control the volume via the stereo. The controls on the unit itself may only be there to set 'limits'.
3. Keep monitoring the DC supply current as you work with the amp. At full volume it could be drawing well over 80A.
4. What power handling rating are the speakers? Prepared to lose them?
5. Have a look at the rear of the circuit boards. You should be able to measure a DC voltage across the terminals of the big smoothing capacitors. Probably looking for +/-30V DC or more. Anywhere close to the voltage rating of the actual capacitors could be expected.

 

[partyanimallighting]

Hi again!
1. Current supply coming in 12VDC. Green POWER LED lit. Voltage display on top of amp displaying 12VDC.
2. The amp is supposed to function without the remote via 1V signal into the RCA line. The controls are there to set gain limits.
3. I'm using a 30A supply. I would think it's more that enough for simple troubleshooting.
4. 200W speakers. Old guys, can be lost.
5. Here's the voltage readouts across the capacitors.

 

[kellys_eye]

32V across the capacitors seems about right to me.

Given that there are four identical amplifiers and the odds on all four going mammaries skywards is relatively low, you should be able to identify ONE complete amplifier section and do comparison readings on the others.

That said, with ZERO output on them it points to something more 'common' to them all - the input signal perhaps?

Close up pictures of topside and bottom side of the pcb(s) might help.

What transistors are being used in the output stage (the big ones bolted to the heatsink)?

 

[partyanimallighting]

Will do. I'll be back.

 

[partyanimallighting]

Thanks kellys_eye!!! The problem was the input connector. I simply retouched all the solder points and viola!!! Back in business!! Thanks again for all your help. I thought I might have had a more serious problem.

 

[kellys_eye]

Great news!