Recapped Sansui AU-719 Protection mode help!

[rasenthiran]

Hi

I had the same issues earlier, sometimes it works good, and then it goes to protection. I sent it to my technician and he said the faults lies around the protection board, under the big 4 power caps

 

[Hipocrates]

I was looking the schematic, and It shows some 2SA1313 and 2SA726, those buggers, gave me headaches on pioneer gear.
Can you take some voltage readings of the 15 and 17, R608 of F-3101 ? I would rebuild that board, kinda of what you did on the 8080.

 

[RR--]

I was looking the schematic, and It shows some 2SA1313 and 2SA726, those buggers, gave me headaches on pioneer gear.
Can you take some voltage readings of the 15 and 17, R608 of F-3101 ? I would rebuild that board, kinda of what you did on the 8080.

Great observation thanks!
So I read a post on how to measure transistors with a multimeter and measured these results on F-3101 in the diode test function mode.
These are the results I came up with, I was a bit confused by what your reply was asking for specifically though

TR604 BE .651v BC .648v
TR605 BE .647v BC .643v
TR607 BE .188v BC 0L EC .596v
TR608 BE .653v BC .644v
TR609 BE .646v BC .641v
TR603 (SCR) BE .639v BC .634v
R 608 4.68ohm


In this video the SCR was a problematic part so I wonder if that could be the cause:

 

[RR--]

I wonder if there are some dry solder joints at play?

I had a good look Pete and it all looks good, that is the main thing the repair technician said he fixed though, he said there was not much he could do as it was an intermittent fault.

Hi

I had the same issues earlier, sometimes it works good, and then it goes to protection. I sent it to my technician and he said the faults lies around the protection board, under the big 4 power caps

Sounds like your repair technician was better than mine haha.

 

[Hipocrates]

Great video, and awesome music too!!

These are the results I came up with, I was a bit confused by what your reply was asking for specifically though

To measure voltages you need to put your DMM, in DC, your negative probe making contact with the chassis and with your positive probe touch certain points of the board (minute 2:00) of the video, with the unit on.






Take notice that you can see every point highlighted on the schematic, correspond to a point on the board, if you read the voltages there, and measure with your DMM it should give you a similar reading. If that reading value is different than the value of the schematic then wen will have a clue of what's going on.

Now, with the resistors usually you need to desolder a leg in order to measure.

http://resistor.cherryjourney.pt/

This is a nice tool to figure out what the colors of the resistors means,

An this little buggers works pretty good to test components (out of circuit) and to learn.
https://www.ebay.com/itm/New-All-in...799298&hash=item4b18017634:g:1pAAAOSw8vZXNJCK

But first is allways good to measure voltages, since the relay seems to be protecting your unit, I bet that you'll be fine.

With your reading seems that your transistors are OK.
Let me know is this make sense, my brain is kind of fried right now.
Hopefully someone with more knowledge will chime in.... if not, we'll manage.

 

[RR--]

Thanks very much for that, the longer I look at it the more sense it makes haha.
I've reassembled the amplifier now, it was tripping in and out of protection mode but after several attempts to power it on it seems to be working fine again. I'll see if it's in protection mode in the morning again and if so measure the voltages then. I assume the amplifier needs to be in protection mode for these measurements to be helpful? The repair tech claimed it always worked when he had it so he couldn't do anything.

It had some problems in 2014 http://audiokarma.org/forums/index....tection-issue-with-my-recapped-au-719.587282/ and some big problems in 2017, always in winter too, If it just keeps on working is there just some general problematic parts I can replace all at once as a shotgun approach in an attempt to find the intermittently faulty part? All of the capacitors are new so that narrows it down.
This amplifier was in pretty mint condition when I got it, it barely even had any Sansui glue to worry about, it's just the unreliability that's doing my head in.

 

[Overundr1]

Strictly from memory here, the protection circuit in this series of amps can be very finicky, often folks assume its in the protection circuit section of the amp when in fact it could be on either driver card. Take a look at the two small value green caps around the L1 coil airc they are around 0.22uf or so and are (i think) c21 and c22. They form part of the lc network and if any one of those 4 fail there will be spurious voltages sent over to the protection board which then trips the circuit. This drove me absolutely bonkers to sort out a while back.
-Lee

 

[Hipocrates]

it's just the unreliability that's doing my head in.

IME, after dealing with 30 vintage units (half of them Sansui), if you want something reliable as daily driver, you need to do a serious reconditioning. Installing some caps won't do it, you need to address the unit asserting a more comprehensive approach, and that usually involves, transistors, diodes, rectifiers, resistors ad sometimes some weird ICs, this is particularly critical with Sansui. Off course this is debatable and can open a can of worms. But at least for me, this is my way to go, check out the work of leestereo as example. All in all were dealing with at least 35years old electronics.

 

[RR--]

Strictly from memory here, the protection circuit in this series of amps can be very finicky, often folks assume its in the protection circuit section of the amp when in fact it could be on either driver card. Take a look at the two small value green caps around the L1 coil airc they are around 0.22uf or so and are (i think) c21 and c22. They form part of the lc network and if any one of those 4 fail there will be spurious voltages sent over to the protection board which then trips the circuit. This drove me absolutely bonkers to sort out a while back.
-Lee

I had a look and on my amplifier C19, C20, C22 are those little yellow critters, C06, C07 and C14 are green however those capacitors aren't listed in the manual.
Do you remember what spec parts they were and what you replaced them with? If you do I'll buy some and just swap them for good measure.

IME, after dealing with 30 vintage units (half of them Sansui), if you want something reliable as daily driver, you need to do a serious reconditioning. Installing some caps won't do it, you need to address the unit asserting a more comprehensive approach, and that usually involves, transistors, diodes, rectifiers, resistors ad sometimes some weird ICs, this is particularly critical with Sansui. Off course this is debatable and can open a can of worms. But at least for me, this is my way to go, check out the work of leestereo as example. All in all were dealing with at least 35years old electronics.

I don't mind doing a more comprehensive rebuild now, I've been using the amplifier daily for 5 years since the recap and sure don't want to get rid of it any time soon. I was only 20 when I originally recapped this and it was the first amplifier I've ever worked on, I've learnt quite a bit since then although I'm still an amateur at best.
I've been going through some of Leestereo's work and it's very impressive.

 

[RR--]

I just started measuring voltages on F-3101 (which wont be easy due to the limited working space)
I found something that doesn't look right, according to the schematic TR604/R615 should read 1.7V to which my reading fluctuated between 1.2 and 1.9 which was in the ballpark,
C605 however should have read 2.1V but I measured 24.55V, it was fluctuating a lot but the amp eventually powered on and settled on 24.55V

 

[skippy124]

Hi,

The voltages around TR604/TR605 will fluctuate when the amp is in protection mode - these two transistors don't play any part in the protection function, they cause the protection led to flash when the amp in is in protection mode, and to stay steady on when the amp is out of protection. Can you measure the voltage rail (shown as 27v on the schematic), with the meter set to measure DC Volts, and then set to measure AC volts. I have seen protection circuit problems when one of the rectifier diodes (D601/D602) has failed open circuit - this results in an excessive AC voltage reading (excessive ripple voltage) on the voltage rail. With regard to your question on the voltage readings on the schematic, these are in the normal operating condition (not in protection).

Cheers
John

 

[RR--]

Hi,

The voltages around TR604/TR605 will fluctuate when the amp is in protection mode - these two transistors don't play any part in the protection function, they cause the protection led to flash when the amp in is in protection mode, and to stay steady on when the amp is out of protection. Can you measure the voltage rail (shown as 27v on the schematic), with the meter set to measure DC Volts, and then set to measure AC volts. I have seen protection circuit problems when one of the rectifier diodes (D601/D602) has failed open circuit - this results in an excessive AC voltage reading (excessive ripple voltage) on the voltage rail. With regard to your question on the voltage readings on the schematic, these are in the normal operating condition (not in protection).

Cheers
John

Thanks again for your advice Skippy, here's some results so far.
All results were measured with the amplifier in protection mode unless stated otherwise. Getting the amp to power on successfully is a bit of a lottery on this cold Melbourne morning.

F-3101 Protector
TR604/R615: Should be 1.7V measured 1.2 - 1.9 fluctuating
C605: Should be 2.1V measured 24.55v when amp through protection mode and powered on
R608: Should be 27V measured 39V in DC mode, Fluctuating wildly between 0L, .57 and 31V in AC mode
R602: Should be 3.7V measured between 37V and 5V fluctuating, 7.3V when amp through protection mode and powered on, (44.6V on other end of R602 resistor)
R633: Should be 1.6V measured 1.776V
R605: Should be 0.02V measured .631V
R609: Should be 6.6V measured 6.645V when amp through protection mode and powered on
D607/TR603: Should be 0.2V measured 357mV

 

[skippy124]

Hi,

Just a quick "recap"

1. Did the amp always have this flaky protection operation?

2. The power supply, including the protection circuit has been fully recapped (electrolytic caps) - did this do anything to resolve (or partially resolve) the flakey protection operation, or did the protection issue start after the recap?

3. The flakiness is worse in cold weather? Is it worse after being switched off for a long period (days/weeks)? Does it improve after a few turn on/turn off operations.

Cheers
John

 

[RR--]

Recap

I bought this amplifier early 2013 and recapped it a few months later. All electrolytic capacitors including bipolar caps, large 4 output caps and 'black flags' were replaced, most fuses are also new as well as the power cable.
http://audiokarma.org/forums/index....th-my-au719-recap-please.520308/#post-6775091
http://audiokarma.org/forums/index.php?threads/finished-recapping-my-au-719.528233/#post-6937377

From then until winter 2014 it had been used daily with fantastic sound quality but occasionally wouldn't power on a couple days of the year.
http://audiokarma.org/forums/index....tection-issue-with-my-recapped-au-719.587282/

Then in winter 2017 (this thread, early on) it started having major difficulties powering on, I took it to a specialist who had it for a few months, he said he couldn't replicate the problem. By the time I finally got it back winter had passed and it worked consistently well for the rest of the year.

In 2018, a couple weeks ago when recapping my 8080 the AU719 started having issues again, the weather had gotten colder and I hadn't used my AU719 for a few days as I was using my newly recapped 8080.

I never encountered any flakiness in the couple months before recapping the amplifier in 2013 other than the usual muddy bass and hissing high frequencies of an un-recapped vintage amplifier.
I have been using it literially every day for 5 years with little issue since and it always sounds fantastic.

To answer your questions specifically:

1. Yes but only in winter for short periods of time, it has gotten worse each year.
2. The recap doesn't seem related to the flakiness of the amplifier in my opinion as it has been good for the most part of 5 years of daily use.
3. The flakiness has only been a problem in winter and after not being used for a few days, I can sometimes get it to power on successfully by switching it on and off several times. It seems to power on more consistently when warmed up with a hairdryer first. When it's on it seems to stay on. Last night I had it running smoothly for several hours. This cold morning I can barely get it to stay on for a minute.

Hope this helps, thanks for the input.

 

[RR--]

I just finished measuring every point listed on the schematics of Protector F-3101 and edited the above previous post to include them, the diode at D607 seems to have a small crack which could be the cause of some problems.

 

[Hipocrates]

the diode at D607 seems to have a small crack which could be the cause of some problems.

D607 is a 10D1, if those are bad you can replace them with MUR240G

 

[Overundr1]

The two caps I mentioned on your pics above are c22, also noted you still have vd1212's installed at position d03, they have been known to fail as well and are replaced with two 4148's in series, although looks like you are honing in on a bad diode in the protection circuit.
-Lee

 

[RR--]

The two caps I mentioned on your pics above are c22, also noted you still have vd1212's installed at position d03, they have been known to fail as well and are replaced with two 4148's in series, although looks like you are honing in on a bad diode in the protection circuit.
-Lee

Thanks for that I didn't notice those little guys, I already have plenty of spare 4148's from my 8080 I can swap in soon. (thanks to Hipocrates)

Do you also recommend replacing other similar diodes such as D01 and D02?
Also C22 isn't listed in the schematics, on the side of the cap it says I02J 50 B_(N). Any idea what would be a suitable replacement? There's 3 on each driver board. Also thanks for the input on that, I think I'll just replace them all as well as any other suspicious parts just to be sure. If anyone else can recommend any parts that might need to go I'll add them to my shopping cart.

 

[RR--]

Also small update about those yellow I02J 50 B_(N) capacitors, C19 and C20 on both boards measured at 38.6ohms, both C22's however measured at 99.9ohms and 101.4ohms even though all 6 appear to be identical.
I can't seem to find anything about these anywhere on the net. Should I just swap them with a regular 40ohm film capacitor? I don't know a lot about film capacitors unfortunately.
Thanks again for the input everyone.

Edit: remeasuring the yellow capacitors removed from the board C22 measured at 1.76nF.

VD1212's replaced with 1N4148's in series. No noticeable effect on protection issue.

 

[RR--]

I'm feeling a bit lost on this so I think the best that I can do at this stage is to just replace every part that is known to have issues. So far the list includes:

F-3101

• D601 & D602 10D2 (1S2227) replace with 1N4003-E2/73 Rectifiers Vr/200V Io/1A
• D607 10D1 replace with MUR240G Rectifiers 400V 2A
• ZD601 replace with 1N5232B Zener Diode 5.6V 0.5W
• ZD602 replace with 1N5234C Zener Diode 6.2V 0.5W
• SCR601 2SF656 replace with MCR100-6A1G SCRs Silicon Controlled Rectifier with reversed pin order
• TR608, TR609 2SC1313, replace with KSC1845FTA
• TR607, TR610, TR611 replace 2SA726 with KSA992FBU

F-2926 and F-2927

• VR01 3386P-1-101LF Bourns Through Hole 3/8IN 100 OHMS 10% 0.5Watts Square Trimmer Resistor
• VR02 3386P-1-471LF Bourns Through Hole 3/8IN 470 OHMS 10% 0.5Watts Square Trimmer Resistor
• VD1212 already replaced with 1N4148
• C19, C20, C22 I02J 50 B_(N), .22uf, not sure of a valid replacement as no capacitors are listed in the schematics.

Any more suggestions? You guys have been a huge help so far, thanks again.