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AU-719 on the bench

AUD101 said:
John, my AU-719 is similar to what you have observed - I noted before recapping, Transformer PT701 (nearest the back panel) measured 44-0-44V, while PT702 measured 41-0-41V (giving approx +/-63VDC and +/-58VDC)

Like you I am thinking maybe the transformer primary taps for PT702 are swapped / mis-wired , and like you did not want to mess with the 'Mains' input selector switch to prove.

I wonder if any other AU-719 (EU / BS models) owners with the 220V / 240V 'Mains' input selector have similar Transformers discrepancies
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Well, well, well - there is some Golden information if I ever saw any!

So, it is possibly 'normal', but maybe just that I have here an extreme example! - as for mains selector input wiring, Switching to 220V with 240V applied caused the voltage output of both transformers to increase - so I think that rules out incorrect wiring - attractive though that idea was.

What amazes me is that subjectively it is difficult or impossible to hear, it doesn't seem to give a channel balance problem - but then maybe my ears may be a bit wonky. :D

@skippy124, @pete_mac - any thoughts guys?
 
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Hyperion said:
Wel, well, well - there is some Golden information if I ever saw any!

So, it is possibly 'normal', but maybe just that I have here an extreme example! - as for mains selector input wiring, Switching to 220V with 240V applied caused the voltage output of both transformers to increase - so I think that rules out incorrect wiring - attractive though that idea was.

What amazes me is that subjectively it is difficult or impossible to hear, it doesn't seem to give a channel balance problem - but then maybe my ears may be a bit wonky. :D

@skippy124, @pete_mac - any thoughts guys?
Click to expand...

The work bench and associated is currently packed away, so let me see what I can do re: setting up some gear and extracting the 719 from storage and taking some measurements
 
I just cross-connected the AC feed from the transformer secondaries to the PSU board (one at a time) - and with the 'good' transformer connected to the 'bad' side, I could see a solid 95V AC - and +/- 63V DC as the rail voltage.

Doing the same thing, but connecting the 'bad' transformer to the 'good' side - I got 87V AC and +/-56V DC as the rail voltage. So the deficit was reduced to 7V DC (from 11V DC) with them swapped - but I think this really does prove that there is something amiss with one of the transformers.
 
Hyperion said:
I just cross-connected the AC feed from the transformer secondaries to the PSU board (one at a time) - and with the 'good' transformer connected to the 'bad' side, I could see a solid 95V AC - and +/- 63V DC as the rail voltage.

Doing the same thing, but connecting the 'bad' transformer to the 'good' side - I got 87V AC and +/-56V DC as the rail voltage. So the deficit was reduced to 7V DC (from 11V DC) with them swapped - but I think this really does prove that there is something amiss with one of the transformers.
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Since disturbing the wires, there seems to be a weak connection somewhere. One slim possibility is a bad crimp in the connector. The other inside the transformer. For the connector there is a "lock tab" holding the plastic on that you poke in with something to release it, then pull it off to expose the crimp to wire connection. You know how to get inside the transformer, but the wires are usually buried deep even with the covers off. Lucky you to get the defective one. :oops:
 
On the chassis parts list (top view) immediately below the transformers PT701/2 there are two 220 ohm 2W NIR resistors R701/2; from the numbering they should be in the transformer circuit somewhere but are not shown in the schematic as far as I can see. Their physical location is in the area of the on/off switch so they must be in the primary circuit if they actually exist.
 
They will very likely be the headphone dropper resistors, they are 220 ohm Mox resistors. Soldered in between the speaker selector switch and the headphone socket so counting as chassis parts. ;)
 
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Hyperion said:
Wel, well, well - there is some Golden information if I ever saw any!

So, it is possibly 'normal', but maybe just that I have here an extreme example! - as for mains selector input wiring, Switching to 220V with 240V applied caused the voltage output of both transformers to increase - so I think that rules out incorrect wiring - attractive though that idea was.

What amazes me is that subjectively it is difficult or impossible to hear, it doesn't seem to give a channel balance problem - but then maybe my ears may be a bit wonky. :D

@skippy124, @pete_mac - any thoughts guys?
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John, I've listened to that amp for 6 years now and my ears are in fine shape. I've never noticed a difference in the channel levels.

If you can't find the fault could you leave the transformer secondaries "crossed" to at least reduce the difference in voltages ? I expect if we didn't notice a difference of 11v we're not likely to notice a difference of 7v.
 
@Hyperion: I don't know if data from a 120V AU-719 would be of any use to you, but here it is: Unregulated power supply voltages (at 122VAC) and bias at ~35mA were: 59.7VDC/13.5mVAC & -59.7VDC/13.5mVAC (left channel) and 59.7VDC/14.1mVAC & -59.5VDC/12.2mVAC (right channel).
 
sansui au719 said:
If you can't find the fault could you leave the transformer secondaries "crossed" to at least reduce the difference in voltages ? I expect if we didn't notice a difference of 11v we're not likely to notice a difference of 7v.
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I can do that, no problem. Mike 'sansui88' is right, I've been turning over in my mind if there are any reasons why I shouldn't - in other words a 'gotcha' that I/we haven't thought of that might make this change undesirable or unworkable - I can't see anything so far. As usual I will make the change reversible, and in keeping with Sansui's way of doing things.

I want to thank everyone for their input, this was a pretty good 'head scratcher' for me, but the hive-mind of AK came through. :thumbsup:
And in other news, the replacement Main Filter capacitors are due to arrive tomorrow! :banana:- so I'll get them in and tested, then I'll make the changes to the transformer wiring.
 
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Hyperion said:
I can do that, no problem. Mike 'sansui88' is right, I've been turning over in my mind if there are any reasons why I shouldn't - in other words a 'gotcha' that I/we haven't thought of that might make this change undesirable or unworkable - I can't see anything so far. As usual I will make the change reversible, and in keeping with Sansui's way of doing things.

I want to thank everyone for their input, this was a pretty good 'head scratcher' for me, but the hive-mind of AK came through. :thumbsup:
And in other news, the replacement Main Filter capacitors are due to arrive tomorrow! :banana:- so I'll get them in and tested, then I'll make the changes to the transformer wiring.
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Might be interesting to measure the difference in sound levels with an SPL meter. Thankfully most vintage Sansuis are owned by men with an ageing acoustic ability (old ears :thumbsup:).
 
The transformer winding crossover is complete, however this had the spin-off that I needed to replace the series pass transistors in the regulated PSU, as they are now getting as hot as they should do - so a refresh there is highly advisable.

The Main Filter capacitors eventually did arrive yesterday - after UPS telling me it would be today! So, I am now sizing up the job of replacing them, they have 'snap in' lugs (no other choice), so I have to increase their wire carrying capacity, I have some special terminals for that. ;)
 
Good news. I wondered what you were up to but I didn't want to poke or pry.

The optimist in me was thinking, "If he's not posting the work must be proceeding well"
The pessimist in me was thinking, "It sure seems mighty quiet around here. Maybe too quiet" - in an inner voice from a John Wayne western

Nice to have a delivery come earler than expected. Enjoy the feeling. What's next after the PSU ?
 
Hyperion said:
The Main Filter capacitors eventually did arrive yesterday - after UPS telling me it would be today! So, I am now sizing up the job of replacing them, they have 'snap in' lugs (no other choice), so I have to increase their wire carrying capacity, I have some special terminals for that. ;)
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Curious what your choice is here. I found it really difficult to make a choice because I wanted to keep the cost low and wanted solder tags/ pins. Found some in the end, F&T 10000 uF 100 v. 40 x 95 mm from Germany.
 
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I searched around a lot, and discovered that Mouser had none in stock of anything suitable, so I had a look on Digikey and came up with these:-

https://www.digikey.co.uk/product-d...nics-cde/382LX123M080N062/338-2109-ND/2295339

12,000µF, 80V

With the space being limited to 40mm diameter, and needing to be 80V or more, there isn't much choice. (I really didn't want to mess about with 35mm diameter replacements).

BTW: I wouldn't have considered any EU suppliers, because of ridiculous import duty charges now being levied on a lot of goods to the UK by EU suppliers. So I only looked at Mouser, Hi-Fi Collective and Digikey.
 
Hyperion said:
I searched around a lot, and discovered that Mouser had none in stock of anything suitable, so I had a look on Digikey and came up with these:-

https://www.digikey.co.uk/product-d...nics-cde/382LX123M080N062/338-2109-ND/2295339

12,000µF, 80V

With the space being limited to 40mm diameter, and needing to be 80V or more, there isn't much choice. (I really didn't want to mess about with 35mm diameter replacements).

BTW: I wouldn't have considered any EU suppliers, because of ridiculous import duty charges now being levied on a lot of goods to the UK by EU suppliers. So I only looked at Mouser, Hi-Fi Collective and Digikey.
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These are the ones I bought. But with transport they got to 9 euro each.
https://www.elpro.org/gb/ftcap-lfa-series/109766-lfa-100-v-10000-f.html
 
I really hope the Impedance in 'Ω' isn't '19' as they seem to indicate - I hope its a misprint for 0.19 that is, if by 'Impedance' they mean 'ESR'. ;)

:)
 
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Hyperion said:
I really hope the Impedance in 'Ω' isn't 19 as they seem to indicate - I hope its a misprint for 0.19 ;)
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They measure around 0.02-0.04, but that's at 100 khz as far as I understand. Capacity is really consistent, all four between 10560-10600. So luckely not on the lowest value the + - 20% allows for.
 
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