Kenwood 1903d

[campolojr]

Amp Powers up but goes into protect right away (power light goes off). Fan stays running. Any help would be appreciated.

IC1
Pin 1: 4.89v
Pin 2: 4.69v
Pin 3: 4.69v
Pin 4: 0.21v
Pin 5: 1.42v
Pin 6: 3.59v
Pin 7: 0v
Pin 8: 15.11v
Pin 9: 0v
Pin 10: 0v
Pin 11: 15.09v
Pin 12: 15.08v
Pin 13: 4.91v
Pin 14: 4.91v
Pin 15: 4.91v
Pin 16: 0v

 

[Perry Babin]

Are you sure that that's the correct model number?

 

[campolojr]

Sorry sir its KAC-1903d

 

[Perry Babin]

Do you mean KAC-9103D?

 

[campolojr]

:-/ Yes Perry Babin it has been a long day thank you! That is what it is.

 

[Perry Babin]

With the amp completely disconnected, measure the resistance between the legs of the individual output transistors (Q187-190). Do you read anything near 0 ohms between the legs of any of those transistors (check each transistor individually)?

 

[campolojr]

Not the most technical so I hope this is what you need (multimeter set at 200k ohms)

187
S to G: 45.4
S to D: Builds 3-15

188
No resistance on any pins

189
S to G: 40.2
S to D: Builds 3-15

190
No resistance on any pins

 

[Perry Babin]

No resistance would mean 0 ohms. Did you read 0 ohms?

Set the meter to the lowest ohms range and re-check the transistors. Check pins 1-2, 1-3 and 2-3.

 

[campolojr]

Okay I have

187
1-2: flashed then went open like i had nothing connected
1-3:same thing
2-3:same thing

188
1-2: 29.2
1-3: 12.8
2-3: 15.3

189
1-2: flashes then acts unconnected like 187
1-3: same thing
2-3:same thing

190
1-2: 27.7
1-3: 11.4
2-3: 15.3

 

[Perry Babin]

Remove 188 and 190 and check them out of the circuit.

 

[campolojr]

188
1-2:same readings
1-3:
2-3:

190
1-2: 121.8
1-3: 106.9
2-3: 16.7

 

[Perry Babin]

188: same as what?

190 is definitely defective.

 

[campolojr]

it acts as if i have not connected anything it has no resistance and okay so definitely replace 190

 

[Perry Babin]

You need to replace all 4 for the amp to be reliable.

Check R199-202.

 

[campolojr]

okay i will replace them all. a
I also am unable to locate r199-202

 

[campolojr]

Okay do I remove R199-202 to check or can they stay in circuit?

 

[Perry Babin]

No need to remove them. Make sure that there are no solder bridges on the pads for the transistors that you removed.

 

[campolojr]

Okay I checked them R199-202 is 10.5 and okay I will make sure no solder bridges. Do you think that FET was the problem? Think If I replace them it will power up?

 

[Perry Babin]

Reinstall the transistor that did NOT have low readings. Clamp all transistors to the heatsink. Remove the two fuses from the amp and install a single 15 amp fuse. Reconnect the amp power, ground, remote and see if it powers up. If it does. measure the DC voltage across the speaker terminals. If it's well below 1v DC, reconnect the speaker and see if it will play at low volume.

If it does, replace the 4 transistors. You will need to apply new heatsink compound between the transistors and the heatsink.

 

[campolojr]

I removed all 4 FETS already for replacement. Do you think I should replace the three and try it? Or wait and get all four in there then try it. I almost lifted a pad trying to get them out so I do not want to mess with it if i dont have to.