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Sansui au 719 haunted.

jFF_Bulbo

jFF_Bulbo

Active Member
hello all.

this sansui au 719 is behaving so creepy...

it came with relay engange problems... at power on relay click on and off many times, after 30 secs it finally engage properly.

i fixed it repairing the divers board, wich were repaired before with no succes and also repairing the power suply for the sansui glue damage.

BUUUUT

now when i activate the "subsonic " switch the relaqy engage off..... even if the eneregy conector of the preamp is diconected

whats is more, the relay engege off even id the transformer is disconected, the purple wires lef side from the bottom wich feed energy to preamp and even with no energy subsonic

DC offset is about 12mv on left channel an 20 mV on right, but once "subsonic" switch is activated dc ofsset jump to -5vdc in left ant -7vdc on right, activating protection.
i tought preamp was faulty so i recaped it, changed the transistors c1313 an a992 for new c1845 and a992. problem persist.

thank you for your help.
 
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The relay is working properly, it's not the relay!
Follow through the schematic and look at the voltage on the subsonic switch. I don't have the schematic in front of me but all it should be doing is shorting out a capacitor. This means there is DC on the input side of the capacitor. so find out where it's coming from.
Also see if it does it with the tone defeat switch in the defeat position or in the "on" position. If it only does it in the On position, C17- C20 are probably bad.
 
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Have you replaced the Thyristor? '2SF656' these are notorious for weird protection circuit issues, 'spurious triggering' being just one of them, they need to be replaced wherever seen. :)

They are used in the AU-519, AU-719, AU-819, AU-919 and a few others of the same era, including Receivers & JDM equivalent models.

I use this:-
STMicroelectronics 'P0102DA 1AA3'

Here:- https://www.mouser.co.uk/ProductDetail/STMicroelectronics/P0102DA-1AA3?qs=H1IiUexEDF2eOmhdqLEUZg==

The pinout is different - so you'll need to cross 2 of the leads, the A, K, G, connections are marked on the board which makes it easier, see the Mouser link above for the datasheet.
 
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Hyperion said:
Have you replaced the Thyristor? '2SF656' these are notorious for weird protection circuit issues, 'spurious triggering' being just one of them, they need to be replaced wherever seen. :)

They are used in the AU-519, AU-719, AU-819, AU-919 and a few others of the same era, including Receivers & JDM equivalent models.

I use this:-
STMicroelectronics 'P0102DA 1AA3'

Here:- https://www.mouser.co.uk/ProductDetail/STMicroelectronics/P0102DA-1AA3?qs=H1IiUexEDF2eOmhdqLEUZg==

The pinout is different - so you'll need to cross 2 of the leads, the A, K, G, connections are marked on the board which makes it easier, see the Mouser link above for the datasheet.
Click to expand...
hello. 2sf656 was changed. i installed MCRT100-6. still haunted...

what is amazing (to me) in about the probles persist even when the board has the energy supply disconected... i cabt figure where the energy to activate protection is coming from once "subsonic" is activated......
 
Since you are having about NEG 5/7DC when activating the subsonic filter, focus on F-3098. You can replace 2SC1313 with KSC1845FTA. Check 2SA992 and if needed replace with KSA992FBU. Match transistors TR01-TR04. Check and replace caps on this board as well. Before changing parts, measure voltages and see if they are close to what the schematic below specifies.

1740150845086.png
 
p4spooky said:
Since you are having about NEG 5/7DC when activating the subsonic filter, focus on F-3098. You can replace 2SC1313 with KSC1845FTA. Check 2SA992 and if needed replace with KSA992FBU. Match transistors TR01-TR04. Check and replace caps on this board as well. Before changing parts, measure voltages and see if they are close to what the schematic below specifies.

View attachment 3433537
Click to expand...
Recap done. Transistor changed for 1845/a992. Still activatinf protección even with no vdc (desconected the conector feom power suply.)
 
Well. Hello again. This Sansui still haunted. Y remove the transistors in the f3098 board and removed the power supply conector. Still activanting protect when subsonic Is activated
 
IMG_20250503_140713.jpgIMG_20250503_140718.jpghello all.
sansui au 719 now sounding good!!!
in the back of F2926 and f2927 there are two traces factory cutted. once i reconected them, the problems appear.

i only needed to restore the previous condition (cutted) and voila!!! now the unit is working properly.
 
So the problem was fixed by connecting the trace that the factory originally cut? I have some factory cut traces in my AU719 and confirmed they are factory original based on other pics Ive seen here and online, they are there for a reason, maybe reconnecting them masked the problem in some way?

Good to hear its working again though!
 
DEFTECHY said:
So the problem was fixed by connecting the trace that the factory originally cut? I have some factory cut traces in my AU719 and confirmed they are factory original based on other pics Ive seen here and online, they are there for a reason, maybe reconnecting them masked the problem in some way?

Good to hear its working again though!
Click to expand...
I think he means he re-cut the traces.

He had repaired the cut traces when restoring and reflowing solder joints.

jFF_Bulbo said:
i only needed to restore the previous condition (cutted) and voila!!! now the unit is working properly.
Click to expand...
 
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