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Help on an sansui x1

w_barton

w_barton

Active Member
hello, I have wrestling with this problem with my Sansui X1 and it has been kicking in the shin. I had plug in the 2 sets of phono boards and this led to losing the -47 and 10 power supply. I managed to fix the-47 by replacing the bridge rectifier. The problem now is the 10 volts supply. There are no DC output from the bridge rectifier but AC is present on the output of the bridge. My first thought was the bridge rectifier's but they were okay. The bridges are the only components on the voltage path before inputting into the power supply board. So I am stumped and I have no solution to the problem. If there is anyone who can help me, I greatly appreciated it and my behind would thank you too for getting rid of the butt kicking.
 
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A symptom like that usually indicates the filter capacitor on the output of the bridge rectifier is open.
 
hello kevzep! Thank you for your assistance in my problem. I am originally from Guam and but now retired in Vietnam. When I take the measurement at Pins 43,45,46, my readings are : pin 43= -.2dc and 20v ac, pin 45=0 dc and pin 20v ac, pin 46= -.1 dc and 10v ac and pin 48 0 volts dc and 10v ac. I replace the respective bridges related to the above pins but the issue still persist. I do not have a scope to measure on those pins, just my old fluke 83.Its really strange since all it is the DC supply and its filters, simple and straight forward, but I have never seen anything like this. Thank you again kevzep for your help in this matter.
 
w_barton said:
hello kevzep! Thank you for your assistance in my problem. I am originally from Guam and but now retired in Vietnam. When I take the measurement at Pins 43,45,46, my readings are : pin 43= -.2dc and 20v ac, pin 45=0 dc and pin 20v ac, pin 46= -.1 dc and 10v ac and pin 48 0 volts dc and 10v ac. I replace the respective bridges related to the above pins but the issue still persist. I do not have a scope to measure on those pins, just my old fluke 83.Its really strange since all it is the DC supply and its filters, simple and straight forward, but I have never seen anything like this. Thank you again kevzep for your help in this matter.
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Have those capacitors on the output of those bridge rectifiers been replaced? Can you remove and measure them?
The only way that much AC can make it through there is for there to be a problem with the bridge, or the caps have to be completely shorted out? But then you wouldn't see that much voltage.
Are you sure the meter is not playing tricks on on you?

Also, disconnect the Pin 44,45,46,47,48 from the regulated supply board to eliminate anything on there which may be affecting the supply voltages.

When you measure again, measure Pin 44 to 43, then Pin 44 to 45.
Then, Pin 47 to 46, and then Pin 47 to 48.
See what you get then.

Also if there is no improvement, I would remove C 09, 10, 11, 12 and see how this affects the readings.


Adding to that, there are a number of components on the F-2778 board which are problematic, fusible resistors, some diodes, they are either MV12, VD1212, these are incredibly unreliable and need to be replaced.
Also, on the two AU-X1's I restored, there was a lot of corrosive glue on the F-2778 board.
These are things to address sooner rather than later.
 
Your discussion of the caps brought me back to them and sure enough, C10 was a cold solder joint. I originally upgraded them and on my way, I did that cold solder. I reflowed all of the 4 capacitors and now she works like a champ. Thank you for the heads up on the diodes, I will go ahead and replace them too. Thank Kevzep for all your time and help on this problem of mine.
 
ghamilton said:
A very special amp!!
Love my 919!
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Thank you GH, I was wanting to add to my sansui collection and I saw a 919 for 8,000,000 Vietnamese dong ($about 300 dollars ). Me thinks that would be my next major purchase. They also had an X11 or X111 vintage
 
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I think I counted my chicken before they hatch. It worked but then it died and returned to its old problematic self. I walked away from it for a time to refresh myself and returned to it later.
I tried measuring some resistance and I accidently touched a cap and it arced! which mean it was charged and it did not discharged to ground. I had 67 volts AC at the input side of the bridge, but the output of the bridge was railing at 90+ volts dc. I went to check the grounds and found some were not connected or open to ground. That is as far as got and I will continue today on my toy. I have done some unique troubleshooting in the past, and I think this ranks right up there with the rest.
 
Personally if the AC input to a bridge rectifier is 67VAC I would expect to see around 90V DC at the output of the bridge, between + & - or 94.7VDC to be a bit more precise, less the forward voltage drop of 2 of the rectifier diodes.
 
Hyperion said:
Personally if the AC input to a bridge rectifier is 67VAC I would expect to see around 90V DC at the output of the bridge, between + & - or 94.7VDC to be a bit more precise, less the forward voltage drop of 2 of the rectifier diodes.
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Yes, that is normal, but where is the 67 VAC coming from? I don't see any output secundaire from the transformers close to that. I would guess it's on DBT and it's measured between positive and negative?
 
GrisPato said:
Yes, that is normal, but where is the 67 VAC coming from? I don't see any output secundaire from the transformers close to that. I would guess it's on DBT and it's measured between positive and negative?
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100V unit fed from 120V (or more) making 52VAC windings output a higher voltage like 67VAC perhaps? - which would then be converted to 90V DC+ a big difference.

That's going to seriously stress the series regulators which get hot even when the voltages are correct.

However if there are grounds missing, or messed around with, this can give rise to weird voltage readings which can be difficult to understand.
 
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So where are you measuring?

Screenshot_20210923-164229_Moon+ Reader.jpg

You mentioned ground 'was' missing from the power supply for the F-2917/2918 boards. Is that where you measured this voltages?!
 
Hyperion said:
100V unit fed from 120V (or more) making 52V windings output a higher voltage like 67V perhaps?

That's going to seriously stress the series regulators which get hot even when the voltages are correct.
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That could be. . . not so smart. I noticed in my search for stepdowntrafo's the sellers recommend 110v for Japanese equipment often if not always. Will work for a hairdryer but not for an audio amplifier!
 
GrisPato said:
I noticed in my search for stepdowntrafo's the sellers recommend 110v for Japanese equipment often if not always.
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That's very poor information given by the sellers, FYI my stepdown outputs 104VAC on load, when fed from UK mains which is nominally ~240V - but just measured as 245.1 at this location. ;)

We'll know a lot more when we find out where our man is measuring those voltages. ;)
 
Hyperion said:
That's very poor information given by the sellers, FYI my stepdown outputs 104VAC on load, when fed from UK mains which is nominally ~240V - but just measured as 245.1 at this location. ;)

We'll know a lot more when we find out where our man is measuring those voltages. ;)
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Yes it is. I had to let them make some, to special order 230/100
 
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