dls cad 11

[rrae]

I cannot get +/- 15v regulated voltage output of regulators. I took a brand new 7915 and 7815 regulators, i get only 13.66V on their inputs. Supply voltage on terminals is 13.88V. The rails are +/- 33.3V. Amp ground terminal as reference. It powers up "fine", no protection. If someone don't have schematic, i can send.

 

[Perry Babin]

If no one can help, post a photo of the board.

 

[rrae]

Right now i can only show the pictures from this topic - http://www.diyaudio.com/forums/car-audio/221953-dls-cad-11-a.html
Later i can send better quality pictures.

 

[Perry Babin]

Those are good enough for now. I don't have the exact diagram but I have something close that may be of some help. Email me and I'll send it to you.

babin_perry@yahoo.com

 

[rrae]

I have mad11 diagram which is almost the same, only difference that "mad" was made for russian market. If You Perry don't have it, i can send it to you.

 

[Perry Babin]

Sure, send it.

 

[rrae]

Check your inbox.

 

[Perry Babin]

The rail voltage is much too low. Are the power supply FETs intact?

Are they being driven properly?

If you don't have a scope, check the drive with a multimeter set to DC volts. You should read approximately 5v with the black probe on leg 3 and the red probe on leg 1. Check the FETs for both power supplies.

 

[rrae]

I did not find any shorts at power supply fets.
They are not driven properly, drive voltage for all fets was 1.38-1,43V.

 

[Perry Babin]

Post the DC voltage on all pins of the SG3525.

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:

 

[rrae]

1. 0.00
2. 4.93
3. 0.01
4. 0.22
5. 2.05
6. 3.47
7. 2.03
8. 4.68
9. 1.36
10. 0.01
11. 1.38
12. 0.00
13. 11.04
14. 1.43
15. 11.04
16. 4.94
Voltage at terminals - 13.38V
Ground as reference.

 

[Perry Babin]

For U305 with the black probe on the center leg, what is the DC voltage on the two other legs?

 

[rrae]

pin 1: 2.40V
pin 3: 28.8V

 

[Perry Babin]

Measure the DC voltage on both halves of U303A.

For one place the red probe on pin 1 and the black probe on pin 2.

The other other side, place the red probe on pin 4 and the black on pin 3.

 

[rrae]

red pin 1, black 2 - 1.01v
red 4, black 3 - 0.43v

 

[Perry Babin]

The opto-coupler and regulator are causing the pulse width to be too low. Confirm that the following resistors are within tolerance (you may have to desolder one terminal to be sure) and that all match the values on the diagram.

R328
R329
R309
R358

 

[rrae]

These resistors are ok.
This dont make sense to me - if i set power supply voltage more than 12.9V - power supply transistors are not drived correctly, by voltage what i did mention earlier - 1,49v.
If i set 12.4v, i get correct drive voltage around 4.96 on all supply transistors. But then i get only -63v rail and still old +33v rail on rectifiers.

 

[Perry Babin]

Are you saying that you get +33v and -63v rails?

 

[rrae]

I might have been wrong, but if i remember correctly, yes, i should recheck then. But i dont understand, why drive voltage is not correct at 13v, but it is correct at 12.4v When drive voltage is "good", i can get negative regulated voltage on regulators and opamps, i do get -14v at 7915, but still old +7v on 7815

 

[Perry Babin]

This amp has a regulated power supply. When the voltage reaches the target rail voltage, it reduces the pulse width so that the rail remains precisely at the target voltage. When the pulse width is reduced, it will read less than 5v. In some amps, it can read as low as a fraction of a volt when the amp is at idle. When you reduce the input voltage, the pulse width has to increase to try to maintain the target rail voltage. When the pulse width increases, it reads as a higher DC voltage.