Crunch GP 3000

[mike49504]

Ok im working on this amp again after putting new + - 5 volt regulators in it.

Im running into the same problem again Amp powers up for a sec then goes straight into protection mode.

Heres what i have done to the amp.

I replaced both 5 volt regulators ( L7805 L7905) I put in a new KA78T12 regulator. I tested output driverboard in another amp and it seem to work fine.

Any ideas on where to start on this amp??

 

[Perry Babin]

Is there any DC on the output filter inductor when it powers up?

 

[mike49504]

I get -104.8 volts on both output filter inductors when powering it up

 

[Perry Babin]

It would appear that you have leaking or shorted outputs if the driver board is OK.

Without the driver board, do you have DC on the inductors?

 

[mike49504]

With no driverboard I have 0 volts on the output filter inductors

 

[Perry Babin]

You stated that the driver board seemed to work right in the other amp. Did the other amp produce clean audio with this driver board installed?

 

[mike49504]

Not sure didnt get that far. All i know is the amp didnt go into protection mode.

I have another driverboard here that should be in 100% working conditon since its brand new

 

[mike49504]

Ok right now im in the process of testing all of the outputs I removed them from the board and im checking all of them ill post back with my results

 

[mike49504]

Ok i tested all of the outputs and all test the same here are the readings.

1-2:OL
1-3:OL
2-3:0.451

Probes reversed
1-2:OL
1-3:OL
2-3:OL

Do you need me to post the voltages on the pads for the output driver board?

 

[Perry Babin]

Please post a photo of the inside of the amp showing the component side of the driver board.

 

[mike49504]

Heres a pic of the driverboard that was in the amp when i got it in for repair.

 

[Perry Babin]

Ok. Post the voltages on the pads for the driver board.

 

[mike49504]

1:0
2:0
3:-119.5
4:-108.3
5:-120.5
6:-0.1
7:-120.7
8:0.1
9:13.7
10:0
11:0
12:-6.8
13:0
14:14.9
15:-121.1
16:0
17:-121.2
18:-109.2
19:-120.9
20:0
21:0

 

[Perry Babin]

Pin 9 should have 5v. It has 13+. Check the regulator.

Pin 12 should have -5v. It has -7v. Check that regulator.

 

[mike49504]

The 7905 and 7805 are to-92 package I have theese on hand if they test bad wondering will theese work??


Digi-Key - 497-1472-5-ND (Manufacturer - L7905CV)


Digi-Key - 497-1443-5-ND (Manufacturer - L7805CV)

And if so the pin config is the same?

 

[mike49504]

Ok out of circuit this is what i get.

KIA79L

1-2:0.569
1-3:OL
2-3:OL

Probes reversed
1-2:OL
1-3:OL
2-3:Ol

KIA78L
1-2:1.036
1-3:OL
2-3:OL

Probes reversed
1-2:1.063
1-3:0.603
2-3:0.532

 

[Perry Babin]

Other than checking for shorts or significant leakage, you can't definitively check regulators with a multimeter unless you have an identical (same manufacturer, possibly would have to be from the same batch) that's known to be good to compare it to.

The 78 'may' be defective since it reads essentially the same from 1-2 but that's only a guess.

 

[mike49504]

Ok i replaced the 78L regulator heres what i have on both of the 5 volt regulators


KIA79L Black probe on leg 1

LEG 2:-15.14
LEG 3: 0.07

78L black probe on middle leg
LEG 1 2.32
LEG 3: 2.98

I also noticed R40 and R41: 10 ohms resistors getting red hot and melting the solder

 

[Perry Babin]

Did you use exact replacements or the TO-220 version?

 

[mike49504]

The 79L is the orginal part Didnt replace it.

The 7805 Is the TO-220 package Im using it for testing