Quantum QSA 1500D

mike49504 · 7th June 2010, 08:38 PM

Im working on this amp. The amp powers up and produces output but very low.

I turned the gain pot up and the amp will stop producing audio. So i sprayed some contact cleaner in it and turned it back and fourth 100 times.

Still have the same problem the amp will work until i turn the gain up and it will stop producing audio. When i turn it back and fourth when the amp is up and running the test speaker will flutter back and fourth .

So to me im thinking i have a bad pot. Would this be correct?

Perry Babin · 7th June 2010, 09:00 PM

It would seem that you have a bad pot but there are other possible problems. I'd suggest checking the output voltage of the op-amps to see if any have more than a fraction of a volt of DC.

mike49504 · 7th June 2010, 09:08 PM

Perry,

Want me to post the voltages on all 4 of the op-amps?

The problem is still there with a differnt pot in circuit

Perry Babin · 7th June 2010, 09:11 PM

Yes. All of the op-amps.

mike49504 · 7th June 2010, 09:31 PM

All of the op-amps are 4558's

1:12.56
2:12.56
3:0
4:-14.66
5:-.01
6:0
7:0
8:1.84

The other 3 read the same.
1:0
2:0
3:0
4:-14.66
5:0
6:0
7:0
8:1.84

Perry Babin · 7th June 2010, 10:02 PM

There's definitely a problem. One op-amp has positive voltage on its outputs but has no positive supply voltage. I would suspect that something is shorting to the output of the amp (solder bridge, etc.) if the voltages you posted are correct.

None of the others have positive supply voltage either. You need to trace this problem back to the 15v regulator to determine where the problem is.

mike49504 · 7th June 2010, 10:15 PM

Ok if i have have theese right they are using C2073 and A940 as the regulators?

C2073
1:1.00
2:49.0
3:0.40

A940
1:-0.94
2:-49.0
3:-0.34

I dont see any solder bridges at all on the amp. Myabye a shorted output?

Perry Babin · 7th June 2010, 10:20 PM

Those appear to be the outputs.

It's not likely to be a shorted output.

If you can't find the regulators, post a photo of the inside of the amp.

mike49504 · 7th June 2010, 10:26 PM

Pin 1 and 2 connect to a C2383 and thoose voltages are

1:14.73
2:5.38
3:2.46

I will get the camera out right now and take a pic of the amp

mike49504 · 7th June 2010, 10:38 PM

Heres the pics of the board.

7th June 2010, 08:38 PM	#1
mike49504 diyAudio Member Join Date: Sep 2006	Quantum QSA 1500D Im working on this amp. The amp powers up and produces output but very low. I turned the gain pot up and the amp will stop producing audio. So i sprayed some contact cleaner in it and turned it back and fourth 100 times. Still have the same problem the amp will work until i turn the gain up and it will stop producing audio. When i turn it back and fourth when the amp is up and running the test speaker will flutter back and fourth . So to me im thinking i have a bad pot. Would this be correct?

7th June 2010, 09:00 PM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	It would seem that you have a bad pot but there are other possible problems. I'd suggest checking the output voltage of the op-amps to see if any have more than a fraction of a volt of DC. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

7th June 2010, 09:11 PM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Yes. All of the op-amps. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

7th June 2010, 10:02 PM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	There's definitely a problem. One op-amp has positive voltage on its outputs but has no positive supply voltage. I would suspect that something is shorting to the output of the amp (solder bridge, etc.) if the voltages you posted are correct. None of the others have positive supply voltage either. You need to trace this problem back to the 15v regulator to determine where the problem is. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

7th June 2010, 10:20 PM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Those appear to be the outputs. It's not likely to be a shorted output. If you can't find the regulators, post a photo of the inside of the amp. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

7th June 2010, 09:08 PM	#3
mike49504 diyAudio Member Join Date: Sep 2006	Perry, Want me to post the voltages on all 4 of the op-amps? The problem is still there with a differnt pot in circuit

7th June 2010, 09:31 PM	#5
mike49504 diyAudio Member Join Date: Sep 2006	All of the op-amps are 4558's 1:12.56 2:12.56 3:0 4:-14.66 5:-.01 6:0 7:0 8:1.84 The other 3 read the same. 1:0 2:0 3:0 4:-14.66 5:0 6:0 7:0 8:1.84

7th June 2010, 10:15 PM	#7
mike49504 diyAudio Member Join Date: Sep 2006	Ok if i have have theese right they are using C2073 and A940 as the regulators? C2073 1:1.00 2:49.0 3:0.40 A940 1:-0.94 2:-49.0 3:-0.34 I dont see any solder bridges at all on the amp. Myabye a shorted output?

7th June 2010, 10:26 PM	#9
mike49504 diyAudio Member Join Date: Sep 2006	Pin 1 and 2 connect to a C2383 and thoose voltages are 1:14.73 2:5.38 3:2.46 I will get the camera out right now and take a pic of the amp

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Quantum Impex	splodgedog	Tubes / Valves	7	29th July 2010 04:17 PM
memphis 1500d	timwebb	Car Audio	4	1st June 2010 01:23 PM
directed 1500d	mike49504	Car Audio	7	22nd December 2009 05:31 PM
mtx 1500d	mike49504	Car Audio	3	5th March 2007 01:15 PM
directed 1500d	mike49504	Car Audio	30	20th November 2006 01:43 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read