AU 20,000 No Power

[Overundr1]

Need verification before you do this, measure across the two yellow terminals but wait for confirmation from others before this step!

 

[sansuilove]

Possibly, be very carefull here working with mains voltage. If you have a switched outlet in the rear of the unit measure ac across the two slots when power is applied.

228 Vac when unit turned off
231 Vac when unit turned on

 

[sansuilove]

Hipocrates :
Yes . That's how I found out R01 is bad.
Which makes me think - what feeds it that can make it fry?
Concerning S702 - I get 180Vac at it on both sides doesn't matter if switch is up or down

What's the best way to check it? I checked continuity and it beeps when it's at 'on' position

Regarding the inrush circuit - would love to hear from you what's that and how to test it
Thanks

 

[w1jim]

Measured R01+R02 on f-2511 :
R01 - 0.9M !!!
R02 - 3.9 ohm
It made me a bit confused because on the resistor it says 3.9K but service manual says 3.9 ohm
Ordered a new pair already

I believe the "K" refers to the resistors characteristics and 3.9 ohm is correct.

 

[Hipocrates]

Regarding the inrush circuit - would love to hear from you what's that and how to test it

I don't know on that amp but in general terms is a circuit to limit the initial current demand of the transformer.
In this case... and Looking the schematic I'll start with C701, which is a 0.01 safety cap, after you already found than R01 an R02 were bad.

the tricky part here is this. (why does voltages are not close to your readings) Let's wait for the new resistors and what others have to say.

 

[Hyperion]

Personally I would want to know the voltages across the all the windings, powered-on, with nothing connected, all the yellow markings on the secondary side, as per Hipocrates' post above. I would also want to verify that both primaries are OK.

 

[sansuilove]

There are 2 groups of wires coming out of the transformer
These are the primaries I believe?

 

[sansuilove]

From the "harmonica terminal" there comes brown wire #4 - it has 228Vac which seems ok per schematic
But yellow wire #2 which seems as should be the same (both going to R01/R02 on F-2511)
It gives only 30Vac)

 

[vigman]

Ok WOAH... I have one of these and let me help you... FIRST Do you have a DBT built ?.... 2nd The 3.9 ohm resistors are part of the SLOW START circuit.
If BOTH of the resistors are not OK, your results will be wonky. I assume you live in a 220 volt area, and to be honest I'm not 100% sure how the windings are configured for 220 I would ASSUME the 2 120 volt windings are in series.... NOW since you ( if I read your post correctly ) you have all the transformer secondaries unplugged, you COULD jump the 2 3.9 OHM resistors ,since there are no loads connected.AND you would still the on board AC mains fuse for protection. Sansui first fame was high quality transformers.. and I doubt it went POOF... The AU 20K is a BA 3K and a CA 3K stuffed in the same box. A Variac would also be useful for testing, since you could ramp power up SLOWLY AND / OR drop your 220 to 110 and test each primary & secondary as a stand alone. I have a OLD thread about my 20 k here ( somewhere ) ........

Mike

 

[vigman]

The inrush is just a current limiter thru the 2 3.9 ohm R-01 & 02 resistors so the caps can start charging ( and not look like such a dead short on initial fire up )...
The 22 volt windings supply power for that slow start / protection circuit.

 

[sansuilove]

Thanks I was getting the feeling I won't get any responses anymore then you came in..

1. I have DBT + Variac
2. only One of the 3.9 ohm 20W is bad (R01) - Ordered new ones.
3. Yes I live in 220V area and I've been running it great for 3 years.
4. I have the secondaries and primaries unplugged .
5. All output transistors are out of amp.
6. How do you suggest me checking if the transformer is not POOF ?

 

[Hyperion]

Make sure all the secondaries are disconnected from anything, but also unable to short out on anything. (make SURE everything is disconnected). Power it up and check the output voltages on each of the secondaries - check that they are in spec' as per the schematic voltages.

However
The primaries will check themselves if you have it set for 220/240V - because they will be in series. However the Soft Start relay won't activate as you have everything disconnected (right?) - so just for this test - and this test only - you may need to connect jumpers across the Soft Start resistors. But first time powered up like this I would do it via the DBT - just in case. If all is well (no bright bulb) then remove the DBT and test as above.

Remember you are dealing with lethal voltages on the primary side at the least, bear this in mind when organising the soft start resistor jumpers.

Any questions - just ask.

 

[vigman]

What John said... another possibility IF the R01-02 test doesn't work as expected you could bring the variac down to 120 V ( with the DBT in line ) and check each primary by itself.....

 

[vigman]

Since 1 of the 2 resistors are open and I ASSUME the 2 120volt PRIMARY windings are in series ( for 220/240 operation ) , I think you would get next to bupkis, nada, zip.....
As John states you do not want to get lit up like a Christmas tree so PLAN YOUR TESTS.. and a remote power switch would be a bonus

 

[vigman]

HMMMMM you state you are ordering 20 watt resistors.. the manual calls for 7 watt, I have 10 watt in my BA 3K and that caused a bit of additional damage when things went south...... And just for my info for your DBT I ASSMUE you have 220 volt bulbs. What wattage are they ? IF you do the 120 volt tests you might want to rethink what bulbs you have in series.. I ALSO ASSUME the DBT is on the secondary of the variac ??

 

[vigman]

Oh as far as the dreaded SPRING, do all your relays have the clear covers on them ??? There should be a spring on the top center of each relay....?

 

[vigman]

I would do a static ohmmeter measurement of the primaries first & document. with nuttin hooked up !

PRIMARY WIRING 240V
BLUE TOP PRIMARY WINDING 1 120V AC HOT OR TOP FOR 240 V HOT
GREEN (100 VOLT IGNORE FOR NOW )
YELLOW BOTTOM PRIMARY WINDING 1 120 NEUTRAL OR TIE TO ORANGE PRIMARY WINDING 2 FOR 240/ 220

ORANGE TOP PRIMARY WINDING 2 120V AC HOT / 240 CT
RED (100 VOLT IGNORE FOR NOW )
BROWN BOTTOM WINDING 2 120 NEUTRAL OR 240 NEUTRAL

FOR 220V
GREEN TOP PRIMARY WINDING 1 100V AC HOT OR TOP FOR 220 V HOT


Primary winding 1
Secondaries
92 V CT ( Blue , gray, blue) +/- 68 ( final drive )
120V CT ( Yellow , green , yellow ) +/- 85 THEN post 2508 reg board +/- 35 +/- 65 ( preamps/ drivers )

Primary winding 2
Secondaries
5.7 volt AC ( meter lights )
22 volt AC (Protection circuit )

 

[vigman]

NOW in your case R01, if open breaks the connection between yellow & orange The 220/240 CT
And R-02, if open breaks the neutral....

 

[vigman]

Where did you go ????

 

[JOMARK911]

He got scared Man!!