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OXAUDIO 1st July 2008 10:40 AM

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.

OXAUDIO 2nd July 2008 08:45 AM

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

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.

east electronics 2nd July 2008 12:19 PM

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 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

RS232 13th October 2012 05:39 PM

I know this is an old thread but I need some help
My SU-A900MK2 is gone to hell.
After some investigation I found 1 diode shorted (replaced all 4 ) and a blown fuse.
It now power on (Stand by) but at soon as I press it the relay that connects the power supply rails goes on and off that is with the light bulb test thingy on the live line without it it just blows the fuse.
Any suggestion ?

OXAUDIO 13th October 2012 06:39 PM

The only thing I can suggest, RS232, is to replace also the ceramic capacitors connected in parallel with the rectifier diodes, as suggested by Sakis. I don't have a circuit diagram to hand, but it's possible that the RSN6000B module(IC502)is faulty. This, IIRC, is the Power amplifier IC, so a fault here could blow the fuse

east electronics 14th October 2012 10:51 AM

Just for the statistics ...

In the age of 47 i make repair work from the age of 16 ( !!) well today i repair an average of 300-400 amplifiers per year .... I am not just cocking ....this info might be useful

so in all my repair career i have repaired just a few of them lets say 4-5 ( keep in mind that this series was a top seller in Greece ) but the latest 6 months i had to repair around 10 with most of them belonging to 40-50 years old costumer so no party animals there ..just casual listeners .

It seems to me that the notorious and now days costly if not unobtainable IC have reached the end of life . The numbers around those amps just dont fit .

If you ever find somewhere the IC please let me know i have 4 of them here waiting before i mode them to real amplifiers .

Kind regards

KatieandDad 14th October 2012 11:44 AM

Not unobtainium yet...

and on E-Bay

RS232 15th October 2012 05:43 PM

Thats a relief because I found 1 supplier (Donberg Electronic) and they ask for $267.19 or 164.95 sterling
Will let what I find out on the amp.


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