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Sansui AU-919 Needs Love.

Alex22 said:
Finally got around to swapping the bolts out on F-2845 for ones that I have nuts for, and putting some connectors on the wires.
She is back together and ready for a first attempt at power up........maybe.........



View attachment 2808909
Click to expand...
Looking good!
Good luck with powering up. You have the option with this amplifier to power it up in stages which I like to do.
You can power up with the separate power supplies plugged in, just pre amp PS, just input stage and VAS ( including bias netwerk) or just the triple Darlington powerstage or combinations. This way you know right away where to look.
 
GrisPato said:
Looking good!
Good luck with powering up. You have the option with this amplifier to power it up in stages which I like to do.
You can power up with the separate power supplies plugged in, just pre amp PS, just input stage and VAS ( including bias netwerk) or just the triple Darlington powerstage or combinations. This way you know right away where to look.
Click to expand...

I like this idea, I know from Ray Gianelli's youtube video that I can isolate the power supply from the output stage by disconnecting four connectors (8 wires) on F-2485.
Can you give a little more information on how to do all of your steps, idiots version?
Like I have said I'm not in a hurry to turn it on so may as well take the long way around.

Right now I consider this amp to be Schrodinger's cat.
 
Here you can see the 1-4 for the outputstage.
Further down, coming from the EI transformer going to driverboard for the input stage and VAS, point 11-12.

Screenshot_20230224-164645_Moon+ Reader.jpg

Then where they are connected to the driver board, red for the toroidal supply,
Green for the EI.

Screenshot_20230224-164936_Moon+ Reader.jpg

Then the second secundary from the EI transformer that goes to board F-2844 and provides the regulated supply for the pre amplifier stages.

Screenshot_20230224-165645_Moon+ Reader.jpg
 
Apparently sorting the garden out is more important than playing with amplifiers. Who knew?

My "so you want me to butcher and suppress mother nature instead" fell on unsympathetic ears.
Sorry Mother Nature I'm just doing what they told me.......................
 
Things are looking a little grim in the amplifier department.

Disconnected from F-2845 the purple, yellow and orange wires that come from the transformer. Disconnected the four (8) wires that go tho the output stage.
On F-2844 I disconnected the 2 yellow and one white wire.
This should take power away from most of the amplifier.

So I put her through the dim bulb tester and flicked the switch. I was greeted by a beautiful bright bulb, that didn't dim.

Ok so is that it for my transformer? shorted internally?

Could the fact that I only have a 60w bulb be giving me a false reading? And how best to test the transformer for a definitive answer to if it is good or not?

P1040217.JPG
 
Didn't expect that!
Just to be sure, DBT is in serie with amplifier?
Second to check to not go chasing ghosts, it looks like the only connection still there is the secundary for the protection board F-2840 through board F-2928. When functioning correctly I do not think this should pull enough current to keep the bulb bright. But there is a rectifier and some filter caps . . .
By the way, I noticed you mentioned the fear of transformer being faulty, any reason for that or just general fear of something unrepairable being broken?
 
On F-2845 D01 is burnt out.
The oval filter capacitor C703 is reading as ‘open circuit’, upon inspection it was shorted internally.
The yellow cables close to D01 have had something done to the connectors previously, not sure why.
I was wondering as this is all in a small area if the yellow cables to the transformer either gave or received a power surge, and if this could have damaged the transformer.


D01 had issues. The 2 yellow cables have been molested.
P1030965.JPG

C703 shorted internally here.
P1040064.JPG
 
If we eliminate faulty repairs by someone, I think the most likely original fault was faulty output transistors. This fault damaged the rectifiers, and repair work or shorted rectifiers damaged the capacitor. I agree with you that such a fault could have damaged the transformer. But Sansui transformers are very well made and generally robust, so 'terminal' damage is less likely. ;)

Now you have found the short circuit, the DBT test should 'pass' and AC voltage checks for the secondary windings, followed by reconnection and DC voltage checks should reveal any issues.
 
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Alex22 said:
On F-2845 D01 is burnt out.
The oval filter capacitor C703 is reading as ‘open circuit’, upon inspection it was shorted internally.
The yellow cables close to D01 have had something done to the connectors previously, not sure why.
I was wondering as this is all in a small area if the yellow cables to the transformer either gave or received a power surge, and if this could have damaged the transformer.


D01 had issues. The 2 yellow cables have been molested.
View attachment 2812242

C703 shorted internally here.
View attachment 2812246
Click to expand...

I am assuming this was before!?
If so, you can remove F-01 on F-2928 to break circuit to the rectifier for the protection circuit.

Screenshot_20230227-135626_Moon+ Reader.jpg
 
GrisPato said:
Just to be sure, DBT is in serie with amplifier?
Click to expand...

The DBT is fine and worked well on my 517 and 717. But I was wondering if my 60w bulb may not work properly with the extra power of the 919. Incandescent bulbs are hard to find locally and I don't have a 100w or 150w bulb.
 
60 watts is fine for a DBT check of transformer functionality, with everything reconnected you may not get protection circuit functionality as 100 watt may be required for that.

With one of the Oval capacitors out of action, you will need to re-stuff at least that one but obviously better to do all of them. For further checks to make sure all is well with the transformer you can substitute the failed capacitor with a spare can capacitor (temporarily wired in), of a few thousand µF if you have one.
 
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Alex22 said:
The DBT is fine and worked well on my 517 and 717. But I was wondering if my 60w bulb may not work properly with the extra power of the 919. Incandescent bulbs are hard to find locally and I don't have a 100w or 150w bulb.
Click to expand...
I thought already it should be ok, just to be sure ;).
 
Hyperion said:
60 watts is fine for a DBT check of transformer functionality, with everything reconnected you may not get protection circuit functionality as 100 watt may be required for that.

With one of the Oval capacitors out of action, you will need to re-stuff at least that one but obviously better to do all of them. For further checks to make sure all is well with the transformer you can substitute the failed capacitor (temporarily wired in), with a spare can capacitor of a few thousand uF if you have one.
Click to expand...

Already re-stuffed all 4 ovals,, replaced F2845 with a less broken one. Removed and tested the output transistors they are all 2SD424, 2SB554. No idea if they are good for this amplifier but am hoping that they will be ok for testing purposes. Replaced all the black flags with cog types, probably didn't get any the wrong way around.:)
 
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