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AU-999 initial powerup, after restoration

Unsoldered the power transformer secondary leads & hooked up the multimeter: I measured

46-47v AC on the purple wires
46-47v AC on the blue wires

Both are supposed to be 30v AC

I guess the PT is shot.

So the flickering power light I noticed earlier may be an indicator of PT health? Even though it's only a 4v circuit?

I checked before disconnecting the PT & was still getting that ground hum through headphones. But only when the amp wasn't connected to a turntable ( I used the 100w 8ohm dummy speaker load this time ). So I'm wondering about those diodes D601, 602 & what their role was.
 
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I'm glad I used 63v caps when I recapped F-1230 instead of the 50v originals. That was getting direct AC from the PT.
 
mmm that is extraordinary.
Is your unit a multivoltage? If so, make sure is on the the correct voltage.
Are you measuring from the center tap to the wire?
 
bolero said:
Unsoldered the power transformer secondary leads & hooked up the multimeter: I measured

46-47v AC on the purple wires
46-47v AC on the blue wires

Both are supposed to be 30v AC

I guess the PT is shot.

So the flickering power light I noticed earlier may be an indicator of PT health? Even though it's only a 4v circuit?

I checked before disconnecting the PT & was still getting that ground hum through headphones. But only when the amp wasn't connected to a turntable ( I used the 100w 8ohm dummy speaker load this time ). So I'm wondering about those diodes D601, 602 & what their role was.
Click to expand...

Hi,

1. just to confirm that you are measuring the above voltages from the purple to purple wires, and the blue to blue wires on the secondary outputs of the transformer.

2. if the answer to 1 above is yes, then have a look at the schematic for the multivoltage mains transformer - the total voltage between each of the purple wires, and likewise between each the blue wires is a nominal 60VAC. Both these purple and blue windings are centre tapped, the purple to purple has a white centre tap wire and the blue to blue has a gray (grey) centre tap wire. The voltage from the centre white centre tap wire to each purple wire, and from the gray centre tap wire to the each blue wires, should be a nominal 30VAC.
Can you recheck the ac voltages on these secondary windings and confirm white to each purple and gray to each blue wire.


NOTE: the symptoms you have described in recent posts point to a failing mains switch, particularly the “sizzling” sound, and the fact that you have noticed that a tuner fed from the switched output on the rear of the amp exhibited flickering of lamps in sympathy with the flickering power lamp on the amp.

I don’t beIieve that the power transformer is “shot”

Cheers
John
 
Well that would be good news!


it's multivoltage: I checked earlier & it's set to 117v, which is correct

1. Yes, was measuring between both purple wires & both blue wires.

Ok will measure from the center taps & report

The sizzling is definitely coming from the power transformer. And thanks!
 
Maybe something is wrong with those outlets on the back? I see two versions of wiring for those, on the improved schem from hifiengine. If there's a short(?) there it might have the same symptoms as a bad switch, since they're all connected? The 4 amp fuse is still good.

And if the power switch is questionable, shouldn't I remove it from the testing procedure?

Thanks again
 
Some PT secondary AC voltage data:

Purple wires to white ( grounded on chassis ):

24v ac on both, PT buzzing.

( I got one reading of 33v off one wire, and the PT was not buzzing. When I doublechecked it to verify, after measuring the blue AC wires, I got 24v & buzzing )

Blue wires to grey ( grey goes to F-1230, no direct ground to chassis ):

24v ac on both, PT buzzing
 
bolero said:
Thanks! It's in the manual: tells you to switch it to any of the mono modes first

Output transistors mounted on big heatsinks inside the amp. Running cool.

The noise only happens with phono selected. I guess it could be related to the volume trimmers at the back, but I've worked them all & they seem to be functioning ok. I'll attach a sound clip, it's not regular TT background noise & wasn't doing it before. At least, I don't think it was...
Click to expand...
I rebuilt a AU-888 and ended up with similar problem on phono only. I took out the 1815’s on the phono board and reinstalled the original 458’s. The problem went away.
 
Hey, thanks!

I *believe* the background noise in phono went away once I replaced the 1815's with 1845's

Right now I think I have 2 problems:

1. The power transformer buzz ( which is being picked up by phono & is different from the old transistor noises ) & PT low AC voltage supply

2. The bad headphone ground hum, that is most noticeable when there isn't a TT connected

They may or may not be related...

*edit forgot to mention: I powered the 999 up without board 1228-1 installed & the PT still buzzed.

I'm going to check out that microswitch on the front power toggle, and that big cap hanging off the power outlets at the back
 
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I looked back at my notes, I can’t believe it was over 6 years ago, but I was wrong on the 1815’s. I initially changed out the 458’s with 1845’s, and that created the noise. I then when back to the 458’s. That solved the noise issue on phono with my 888.
bolero said:
Hey, thanks!

I *believe* the background noise in phono went away once I replaced the 1815's with 1845's

Right now I think I have 2 problems:

1. The power transformer buzz ( which is being picked up by phono & is different from the old transistor noises ) & PT low AC voltage supply

2. The bad headphone ground hum, that is most noticeable when there isn't a TT connected

They may or may not be related...

*edit forgot to mention: I powered the 999 up without board 1228-1 installed & the PT still buzzed.

I'm going to check out that microswitch on the front power toggle, and that big cap hanging off the power outlets at the back
Click to expand...
 
Ok thanks! I powered up the amp without board 1228 installed, and I was still getting transformer buzz. So I don't think it's 1228 anymore. Not ruling it out though.

I checked out the microswitch at the front power toggle, and it must need voltage to work as I never got continuity thru it regardless of the power toggle being on/off.

And that cap on the switching power inlets at the rear breaks the power to the multi-voltage selector. I'd like to get rid of that cap anyway, and lose the switching inlets. It also seems to be another point of failure.

Any reason not to replace it with a wire, so all the power inlets have wall voltage?

My next step will be bypassing that microswitch and the front power toggle altogether, so the amp will just get wall voltage. I can run it off a switched powerbar, to test the transformer on 120v without any of that stuff inline. I will be extremely careful.
 
Well allright: 33.6 Volts AC, and no transformer buzzing, from both pairs of secondary wires! Blue & purple.

So it is probably that microswitch. I saw a part # for it here somewhere, will post a link for posterity.
 
Ps I think that cap at the back needs to be there, to work with the power switch. But I should be able to get rid of the switching outlets. In any case I'll get the amp working before looking into any of that.
 
More good news: I did a quick check with the headphones only, phono sources selected, no TT hooked up, and the ground noise that occurred whenever I touched a knob or the chassis, is gone.

So either this microswitch or the power toggle were the cause of that, too.
 
What are those microswitches, anyway? Do they have a voltage regulator in them or something? Why would it make my power transformer sound like the windings were shorting out?

If it was a relay, I would think it'd either work or not work. Not sputter & affect the amount of voltage passed thru?
 
bolero said:
What are those microswitches, anyway? Do they have a voltage regulator in them or something? Why would it make my power transformer sound like the windings were shorting out?

If it was a relay, I would think it'd either work or not work. Not sputter & affect the amount of voltage passed thru?
Click to expand...
Off the top of my head, those things are just switches and are not active components, so there are no regulators in them. Without looking at the schematics, I'm guessing they're shorting other line level signals to ground when you switch to phono so it would not cause any noise.
 
Ok thanks!

This thing sounds good again: I just ran a CD player into aux, with headphones connected & 2x multimeters monitoring the bias. I reset the bias as the PS voltage was probably suspect the last time. I get a solid +/- 44v off the rectifier now.

I'm tempted to just run it off a powerbar & screw the switch+microswitch.
I soldered together, shrinktubed, then taped up the 2 wires from the microswitch. The microswitch only had those 2 wires attached, so it wasn't grounding anything. The front panel switch might though....actually that's what those D601,602 diodes did apparently: ground the TT when it wasn't selected. But Sansui stopped using them for some reason.

Big thanks to skippy124, for the tip on that switch symptom!!
 
Another question: while I wait for parts I'm going to replace all the old 2SA640 transistors in the 1208, 1209, boards ( listed as XA495 in schematic ) with new KSA992, should I bother matching any of them?

Thx!
 
Well I went ahead & replaced them, the ones I did check were pretty close but I didn't bother matching any.
 
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