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Old 21st December 2012, 04:58 PM   #11
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just a couple of things

together with the things you do you will probably need to recap the all unit ..Your amp is quite old and since you invest time and money on it make sure that will last longer .

I presume that for symmetry reasons you will change all the transistors and working ones also

Finally changes like the above and even though 15003-4 + 15031-32 combos are extremely rugged devices in practice proved to produce far more rough sound next to their Japanese cousins

In your case i would go for 1943 5200 with 13xx 47xx drivers recap the amp add better decoupling take care of input capacitors and filters work with miller caps and so on

Kind regards sakis
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Old 21st December 2012, 05:48 PM   #12
jaycee is offline jaycee  United Kingdom
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I checked a few places and it is recommended to use MJ21193/4 outputs on this amp. I wouldn't like to risk substituting faster devices. Also mounting TO-264 flatpack devices to the heatsinks could be a pain. The MJ15003/4 should be enough to get it to work, though.

I would agree on the electrolytic capacitors, they are probably at the point where they require replacing due to age. It's never good when you get an amp that is "struck by technician" who didnt know what they were doing

The biggest problem you will have is if the input dual FET, the 2SK97 is damaged. They are pretty much unobtainium along with any decent audio quality small signal FETs these days. Fortunately all the other parts can be substituted fairly well.
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Old 21st December 2012, 07:10 PM   #13
mcd99uk is offline mcd99uk  United Kingdom
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I too noticed that the MJ21193/4 is being suggested as good replacements. Read that oscillation could be a problem with the faster devices. Mounting the different packages would extra work but probably not too difficult as there is plenty of space.

Fortunately, the input fets appear to be ok or at least the input side of them is functioning ok.

I suspect that the abuse this amp sustained weakened some of the devices. Then to have the protection pcb partially disabled just masked the fault(s) rather than fix them. It never sounded right after the initial "repair".

Oh well, next step would be to replace the fusible resistors.
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Old 21st December 2012, 10:03 PM   #14
jaycee is offline jaycee  United Kingdom
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id probably use ordinary metal films to repair with. fusibles seem to be hard to get. As long as you take steps to limit potential fault current, you should be OK. Using a pair of bench supplies would be an excellent way.
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Old 23rd December 2012, 07:46 PM   #15
mcd99uk is offline mcd99uk  United Kingdom
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Success!!!!!!! I have a working sansui again. Replaced all the fusibles in both channels and the drivers + outputs in the blown channel and I have sound and pretty good sound as well (given that its driving some coda 7s with a really naff cd player)

Next step, change drivers in other channel and decide what output transistors to use and which electrolytics to replace and what type. Thinking either Panasonic FCs or Rubycon ZAs?

Also, reinstate the protection circuit properly but that will be another day.
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Old 23rd December 2012, 09:26 PM   #16
jaycee is offline jaycee  United Kingdom
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Glad to hear you've cracked it well done!

Both of those capacitor types you mention are good quality. I have a slight preference for the Panasonics but that is based on price and availability.

I'd suggest, even if the other channel is working OK with the original parts, to replace the drivers and outputs the same, so that they match.

CPC should have all the parts you need
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Old 24th December 2012, 03:57 PM   #17
mcd99uk is offline mcd99uk  United Kingdom
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Jaycee, thank you for your help. It is much appreciated.

Panasonic FCs are my favourite too for the same reasons. They represent good value for the performance.

Yes will definitely do the changes to the other channel as there is a noticeable difference in sound quality. The modded channel sounds much sweeter even with MJ15003/4.

Farnell is my first choice of supply or RS (but they do not seem to stock the MJ21193/4) as they have a trade counter near by.
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Old 24th December 2012, 04:10 PM   #18
jaycee is offline jaycee  United Kingdom
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CPC, Farnell, same thing pretty much RS tend to be overly expensive I find.
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Old 25th December 2012, 11:19 AM   #19
RS232 is offline RS232  United Kingdom
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Need some help please....
Well is not an AU517 but is a Sansui 5050
My problem is the protection circuit is always on and I get nothing in the output.
I have checked everything
Removed end measure output transistores and drivers
Changed most of the capacitors on the amp board
Everything measure/tested fine and the DC offset before the relay is only 5mV on each channel.
Tested the protection circuit, replaced capacitors and cant fine anything wrong with it.
The only thing I fine a bit odd is the transformer voltages.
There are 3 different voltages, 1 with 6.3V for the light bulbs in the front panel (Ok)
1 symmetric for the pre/tuner stage (OK)
the last one is symmetric for the power stage and is off, there is a +/-4V difference between rails.
Can this cause the protection circuit to quick in ?

Merry Christmas
Ric
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Old 26th December 2012, 12:02 PM   #20
RS232 is offline RS232  United Kingdom
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Problem solved and amp working fine

Thanks
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