Alpine MRP-F300 amp is dead, need help with repair

gexamb

Member
2009-08-28 7:28 am
Well I have had this amp for almost 2 years now. One day it just stopped working. Diagnosis: receives power, light turns on, no output to speakers. I tested with different signal inputs and still no output.

I don't know where to get started. A while back a Mr. Perry Babbin helped me with another amp of mine and it worked great. I hope you will see this Perry and help me again. Here are some pics.

http://img155.imageshack.us/img155/2416/dscn1235l.jpg
http://img818.imageshack.us/img818/9669/dscn1237.jpg
http://img98.imageshack.us/img98/274/dscn1238w.jpg
http://img297.imageshack.us/img297/4057/dscn1239.jpg
http://img411.imageshack.us/img411/7721/dscn1240y.jpg
http://img199.imageshack.us/img199/8550/dscn1241m.jpg
http://img231.imageshack.us/img231/1010/dscn1242.jpg
http://img87.imageshack.us/img87/2577/dscn1245.jpg
 
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gexamb

Member
2009-08-28 7:28 am
The top transistors are all 9.3v, the bottom left ones are 9.3, and the bottom right ones are 11.3. Refer to the picture for a better look.

Although I did not see any negative polarity. My dmm usually has a neg sign next to the voltage reading. Am I supposed to switch the probes around to check for neg polarity? (Red to ground, black to pin?)

Are these the transistors you were talking about? see below
 

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gexamb

Member
2009-08-28 7:28 am
Actually the power FETs are 11.6v all around not 11.3v. I take it the first leg is the very left one looking at it from the picture I posted. All FETs show 0v exactly and to make sure I also checked the other legs as well (the very right ones) and they were 0v as well.

Also, the other transistors I originally checked also have a negative polarity of 9.3v all around.
 

gexamb

Member
2009-08-28 7:28 am
Post the DC voltage for each pin of the driver IC (..494). Place the black meter probe on the amplifier's ground terminal. Place the red meter probe on the point where you need to measure the voltage.

IC#
Pin 1: 8.1
Pin 2: 2.43
Pin 3: 4.51
Pin 4: 3.94
Pin 5: 1.4
Pin 6: 3.59
Pin 7: 0
Pin 8: 11.56
Pin 9: 0
Pin 10: 0
Pin 11: 11.56
Pin 12: 11.56
Pin 13: 4.9
Pin 14: 4.9
Pin 15: 2.43
Pin 16: 0.04
 

gexamb

Member
2009-08-28 7:28 am
All power FETs have 0v at leg 3 on the 200m level which is the lowest my dmm goes. There is also 0.1v on leg 1 however. I also noticed that there is 1.9v running when I probed the case. Does that mean there is a minor short somewhere? Remember all these readings are in the 200m range.
 

gexamb

Member
2009-08-28 7:28 am
Well Perry we found the culprit. One of the main copper lines fried apart. Theres a good 2 inches of the circuit that has peeled off the board. Looks like the circuit from the transformer.

The last pictures shows it really well.

http://img801.imageshack.us/img801/4002/dscn1250n.jpg
http://img408.imageshack.us/img408/8227/dscn1251.jpg
http://img693.imageshack.us/img693/6599/dscn1256r.jpg
http://img149.imageshack.us/img149/5273/dscn1257t.jpg

The amp has overheated in the past at least 10 times no more than 20 tho. It has overheat protection because it shuts off when it gets hot and turns back on after a minute or two. Could this be the problem? Is this even repairable? I was thinking of running a piece of wire from beginning to end and bypass all the discolored and burnt spots.
 
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