Technics SU-A900Mk2

OXAUDIO · 1st July 2008, 10:40 AM

Info. needed on the above, please - I was not sure whether to post this under 'Solid State' or 'Chip Amps' - anyhow a circuit diagram, plus info.(pin-outs & block diagram) for the RSN6000B Mosfet Module(IC502) would be helpful. I am in process of repairing an SUA900Mk2 in which the mains fuse T1 (3.15AT) had blown, the only other known fault being that D702(original type P300D) was short circuit. D 701, 03, & 04 'cold' check OK, but I have replaced all 4 with 1n5408 diodes. I don't know why one diode of 4 in the main Bridge rectifier would fail s/c, and have yet to power up and test the amp.

OXAUDIO · 2nd July 2008, 08:45 AM

Problem solved! After making some further checks, I found that the only fault was the short-circuit rectifier diode and blown mains fuse. I replaced all 4 original diodes with 1N5408s, and the blown fuse. The amplifier is now working perfectly on test as I type this, but I still do not know why ONE diode of four in a conventional Bridge Rectifier should go s/c

linuxguru · 2nd July 2008, 09:03 AM

If the failure occurred, for instance, due to an output short, then it depends on the phase of the input AC supply at the moment the short occurred. The two input rectifiers that were conducting at the time of the short are likely to fail first - in this case, one of them failed first, followed by the fuse blowing and protecting the others. That's why the others did not fail.

sakis · 2nd July 2008, 12:19 PM

almost the same problem and in this case replacing all diodes is the best to do but in my case the problem started from the small ceramics togther with the diodes ...one of them failed then the diode then the fuse ....

replaced all of them...and done

OXAUDIO · 2nd July 2008, 08:26 PM

Thanks to both Linuxguru & Sakis. Must admit I hadn't thought about 'cause and effect' to quite that extent. The amplifier has now been test run for about 4 hours continuously with no repetition of the failure, so all's well that ends well

1st July 2008, 10:40 AM	#1
OXAUDIO diyAudio Member Join Date: Sep 2006	Technics SU-A900Mk2 Info. needed on the above, please - I was not sure whether to post this under 'Solid State' or 'Chip Amps' - anyhow a circuit diagram, plus info.(pin-outs & block diagram) for the RSN6000B Mosfet Module(IC502) would be helpful. I am in process of repairing an SUA900Mk2 in which the mains fuse T1 (3.15AT) had blown, the only other known fault being that D702(original type P300D) was short circuit. D 701, 03, & 04 'cold' check OK, but I have replaced all 4 with 1n5408 diodes. I don't know why one diode of 4 in the main Bridge rectifier would fail s/c, and have yet to power up and test the amp.

2nd July 2008, 08:45 AM	#2
OXAUDIO diyAudio Member Join Date: Sep 2006	Technics SU-A900Mk2 Problem solved! After making some further checks, I found that the only fault was the short-circuit rectifier diode and blown mains fuse. I replaced all 4 original diodes with 1N5408s, and the blown fuse. The amplifier is now working perfectly on test as I type this, but I still do not know why ONE diode of four in a conventional Bridge Rectifier should go s/c

2nd July 2008, 12:19 PM	#4
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	once happend ..... almost the same problem and in this case replacing all diodes is the best to do but in my case the problem started from the small ceramics togther with the diodes ...one of them failed then the diode then the fuse .... replaced all of them...and done __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

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2nd July 2008, 09:03 AM	#3
linuxguru diyAudio Member Join Date: Sep 2007	If the failure occurred, for instance, due to an output short, then it depends on the phase of the input AC supply at the moment the short occurred. The two input rectifiers that were conducting at the time of the short are likely to fail first - in this case, one of them failed first, followed by the fuse blowing and protecting the others. That's why the others did not fail.

2nd July 2008, 08:26 PM	#5
OXAUDIO diyAudio Member Join Date: Sep 2006	Thanks to both Linuxguru & Sakis. Must admit I hadn't thought about 'cause and effect' to quite that extent. The amplifier has now been test run for about 4 hours continuously with no repetition of the failure, so all's well that ends well

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