Kenwood amp in protect, stumped

Justinh722 · 3rd October 2011, 03:54 AM

A friend of mine decided to run his kenwood amp at 1 ohm when it's only 2 ohm stable. The amp didn't go up in smoke, just went in protect. I took it apart and tested the power fets and the output transistors and some driver transistors and they all tested good. The only thing I'm questioning is the rectifiers. They are reading about .221 voltage drop which seems a little low.

Powering up the amp doesn't blow the fuse, nor will it blow the 5 amp fuse I have inline with the B+. Any suggestions? The amp is the kenwood KAC-8104d.

Justinh722 · 3rd October 2011, 05:57 AM

Figured out the protect problem but the amp won't produce any audio.

Perry Babin · 3rd October 2011, 08:17 AM

Does it have positive and negative rail voltage on the output transistors?

Justinh722 · 3rd October 2011, 08:31 AM

Yea it has 12 volts positive and negative on the outputs. I also tested the power fets and I got 61 volts on 2 of the 4 fets. The other 2 read nothing.

Perry Babin · 3rd October 2011, 08:44 AM

The 'power supply' FETs are the ones with 12v.

The ones with 61v are the outputs. Did you check all 3 legs of the other outputs to see if any had -61v?

Justinh722 · 3rd October 2011, 08:55 AM

I always get them mixed up. I do get -61 volts on the 2 outputs that don't have positive voltage on the center leg. I get -61 volts on legs 1 and 2 of both those transistors.

I also tested these output transistors part numbers C4883A and A1859A. I get 11 volts on the first 2 legs of A1859A and -9.8 volts on the first 2 legs of C4883A. The set of 4 outputs are FB31N20D's.

Perry Babin · 3rd October 2011, 11:50 AM

The 4883 and the 1859 are not output transistors. They are being used as the pass transistors for the 15v voltage regulators.

On Q411 and Q413, you should have had -rail voltage on legs 1 and 3. Recheck this.

In the future, give the circuit board designations (silkscreened on the board next to the transistor) for all transistors that you mention.

Justinh722 · 3rd October 2011, 04:29 PM

Q411 and Q413 did have - rail voltage on legs 1 and 3.

Perry Babin · 3rd October 2011, 04:35 PM

Do you have a scope?

Justinh722 · 3rd October 2011, 04:36 PM

That's one thing I don't have yet.

3rd October 2011, 03:54 AM	#1
Justinh722 diyAudio Member Join Date: Sep 2009 Location: Iowa	Kenwood amp in protect, stumped A friend of mine decided to run his kenwood amp at 1 ohm when it's only 2 ohm stable. The amp didn't go up in smoke, just went in protect. I took it apart and tested the power fets and the output transistors and some driver transistors and they all tested good. The only thing I'm questioning is the rectifiers. They are reading about .221 voltage drop which seems a little low. Powering up the amp doesn't blow the fuse, nor will it blow the 5 amp fuse I have inline with the B+. Any suggestions? The amp is the kenwood KAC-8104d.

3rd October 2011, 08:17 AM	#3
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Does it have positive and negative rail voltage on the output transistors? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

3rd October 2011, 08:44 AM	#5
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	The 'power supply' FETs are the ones with 12v. The ones with 61v are the outputs. Did you check all 3 legs of the other outputs to see if any had -61v? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

3rd October 2011, 11:50 AM	#7
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	The 4883 and the 1859 are not output transistors. They are being used as the pass transistors for the 15v voltage regulators. On Q411 and Q413, you should have had -rail voltage on legs 1 and 3. Recheck this. In the future, give the circuit board designations (silkscreened on the board next to the transistor) for all transistors that you mention. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

3rd October 2011, 04:35 PM	#9
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Do you have a scope? __________________ 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

3rd October 2011, 05:57 AM	#2
Justinh722 diyAudio Member Join Date: Sep 2009 Location: Iowa	Figured out the protect problem but the amp won't produce any audio.

3rd October 2011, 08:31 AM	#4
Justinh722 diyAudio Member Join Date: Sep 2009 Location: Iowa	Yea it has 12 volts positive and negative on the outputs. I also tested the power fets and I got 61 volts on 2 of the 4 fets. The other 2 read nothing.

3rd October 2011, 08:55 AM	#6
Justinh722 diyAudio Member Join Date: Sep 2009 Location: Iowa	I always get them mixed up. I do get -61 volts on the 2 outputs that don't have positive voltage on the center leg. I get -61 volts on legs 1 and 2 of both those transistors. I also tested these output transistors part numbers C4883A and A1859A. I get 11 volts on the first 2 legs of A1859A and -9.8 volts on the first 2 legs of C4883A. The set of 4 outputs are FB31N20D's.

3rd October 2011, 04:29 PM	#8
Justinh722 diyAudio Member Join Date: Sep 2009 Location: Iowa	Q411 and Q413 did have - rail voltage on legs 1 and 3.

3rd October 2011, 04:36 PM	#10
Justinh722 diyAudio Member Join Date: Sep 2009 Location: Iowa	That's one thing I don't have yet.

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
Stumped on RF Punch 100 DSM amp - help	m109ner	Car Audio	77	19th June 2011 01:41 AM
Amp goes into protect mode on high notes	legalizeeit 420	Subwoofers	14	18th January 2011 06:19 AM
Amp keeps going into protect mode...	legalizeeit 420	Car Audio	30	19th December 2010 09:24 PM
Stumped Troubleshooting Amp	salesmonster	Chip Amps	4	22nd December 2007 05:50 PM
amp goes to protect, why?	eeyore757	Subwoofers	6	21st March 2007 11:29 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