Sansui AU-717 - Need a little help

[evan_wd]

I acquired a 717 with the left channel being I guess distorted, but also sounded like only partial signal. The little sound that was coming through the left channel was obviously less volume than the right. When used as only an amp, both channels work fine. I thought it might be in the preamp (F-2720) section, so I recapped that as well as replaced some transistors, diodes, and fusistors. No change. I then moved on to the power supply board F-2663. I replaced all of the electrolytics and removed the corrosive glue and everything it touched. Also on that board, some resistors, diodes, the relay, and the sc1708 transistors. No change. Recapped F-2723, as well as replaced diodes, and fusistors, no transistors yet on that one. No change.

Where I messed up was not checking voltages before I started this process. On the PS board F-2663 voltages are as follows:

pins:
24,26= -33.62
18,20= +34.42
17,19= +34.74
23,25= -.812

TR02= E +35.14
C +55.19
B +35.76

TR04= E -34.04
C -56.50
B -34.66

TR03= E -1.070
C -57.30
B -1.645

TR01= E +35.37
C +55.85
B +35.98

What's going on with those low voltages? Is it possible that TR03 is bad? Or is it something farther upstream?
I don't want to continue replacing parts until I get the problem figured out like I should have at the beginning. Thank you for any help you can give!

 

[petehall347]

base emitter voltages look about right .
stand by

 

[petehall347]

tr07 and tr11 voltages should help see whats wrong .

 

[evan_wd]

TR07 E= -1.665
C= -57.73
B= -2.186

TR11 E= .002
C= -2.196
B= -.634

 

[TupolevFan]

It looks to me that TR11 is opened (or shorted)and keeps darlington pair (TR07 and TR03 and those seem normal to me) near cut off. The fault may be in R31 R33(those might be open), R35 - i doubt it because i yet to see shorted resistor but still check or in the transistor(likely TR11) themself . Or C21 is shorted. Another unlikely posibility is R21 but check it as well. This is assuming there is no short somewhere else in the amp but i think in this case TR03 and R23 would be smoking )) if they stay cool then short is unlikely. And after all check for traces continuity especially around components mentioned above R31,R33,R35

 

[evan_wd]

R31 was one of the resistors I changed because it was touched by the corrosive glue, so it tested ok. Although every piece I removed that was affected by glue tested ok. Even all of the fusistors were well within spec. Anyway, all of the resistors you mentioned tested ok except for R33. It started at 114kO and slowly climbed until I stopped measuring at 300kO. Is that because it was still in circuit? If so, I'll have to wait until after work tomorrow to remove it and test out of circuit. I also have a TR11 replacement on hand if I need to replace that. TR03 isn't smoking, but it's heatsink is noticeably warmer than the others...

 

[vigman]

I'm not sure how you are set up.....is the board out of the unit? Anyway make sure pin 21 does hit chassis ground . I am a bit confused 23 & 25 are the -33 v supply.
Which are TR-03 07 & 11. I would pull TR-11 and test that PLUS make sure that you have ~13 volts across ZD-01.....I just went thru this in my " Oh you dirty girl " post

 

[TupolevFan]

R31 was one of the resistors I changed because it was touched by the corrosive glue, so it tested ok. Although every piece I removed that was affected by glue tested ok. Even all of the fusistors were well within spec. Anyway, all of the resistors you mentioned tested ok except for R33. It started at 114kO and slowly climbed until I stopped measuring at 300kO. Is that because it was still in circuit? If so, I'll have to wait until after work tomorrow to remove it and test out of circuit. I also have a TR11 replacement on hand if I need to replace that. TR03 isn't smoking, but it's heatsink is noticeably warmer than the others...

R33 according to SM should be 22K unless you accidentally measured something else it shouldn't be more than 22K even in a circuit and definitely would be the reason of low negative rail in this case. And yes the change of value which you see ( 114k -> 300k) can be due to some capacitance when you measure "in" circuit. But again 114k or 300k is just too high

 

[Hyperion]

Another thing to check would be R11 (10KΩ) and R13 (10KΩ) they are physically right next to the capacitors that get slathered with corrosive glue and often take a hit (leads eaten through) as a result, (TR07 B= -2.18V ?). R33 (22KΩ) being 'open' (apparently) definitely won't help though.

 

[evan_wd]

I'm not sure how you are set up.....is the board out of the unit? Anyway make sure pin 21 does hit chassis ground . I am a bit confused 23 & 25 are the -33 v supply.
Which are TR-03 07 & 11. I would pull TR-11 and test that PLUS make sure that you have ~13 volts across ZD-01.....I just went thru this in my " Oh you dirty girl " post

The board is in the unit with all wires attached. I saw your thread previously and checked that I do have 13V on zd-01. I can probably pull TR11 tonight after work.

R33 according to SM should be 22K unless you accidentally measured something else it shouldn't be more than 22K even in a circuit and definitely would be the reason of low negative rail in this case. And yes the change of value which you see ( 114k -> 300k) can be due to some capacitance when you measure "in" circuit. But again 114k or 300k is just too high

I think I have mistyped. Looking at the pictures on my phone since I'm at work, I'm pretty sure R33 is the one that I changed, and R31 is reading high in circuit. I believe it's supposed to be 6.8K. I'm assuming that does not change the fact that the reading shouldn't be that high. I'll double check when I get home. I'm not sure if I have any of those on hand, I may have to order some. But I'll try and remove it tonight and test it again.

Another thing to check would be R11 (10KΩ) and R13 (10KΩ) they are physically right next to the capacitors that get slathered with corrosive glue and often take a hit (leads eaten through) as a result, (TR07 B= -2.18V ?). R33 (22KΩ) being 'open' (apparently) definitely won't help though.

R11 and R13 have already been replaced because of the glue you spoke of. They were both corroded, but tested well if I remember correctly.

Thank you all for the valuable input, I feel like I might be getting somewhere with this! I'll do some more testing tonight and update from there.

 

[TupolevFan]

The board is in the unit with all wires attached. I saw your thread previously and checked that I do have 13V on zd-01. I can probably pull TR11 tonight after work.



I think I have mistyped. Looking at the pictures on my phone since I'm at work, I'm pretty sure R33 is the one that I changed, and R31 is reading high in circuit. I believe it's supposed to be 6.8K. I'm assuming that does not change the fact that the reading shouldn't be that high. I'll double check when I get home. I'm not sure if I have any of those on hand, I may have to order some. But I'll try and remove it tonight and test it again.

R31 if opened would have the same effect as opened R33. And if you measured it correctly then replacing it should bring negative rail back to normal

 

[vigman]

If the leads are not destroyed ( like 1/2 the metal gone ) scrape em with an xacto knife and remeasure em, then you can use that till your replacements arrive.....

 

[evan_wd]

Update! Thank you all for the advice! I removed R31 and measured it. It was OL, good news! Since I didn't have any new or old 6.8k resistors I took a 22k and a 10k and wired them in parallel which gave me 6.9k, close enough. 33.6V on pins 23,25. -34.6 on TRO3. What a huge relief! Sounds so good with a quick headphone test that it almost brings a tear to the eyes. I'll be gone the next 2 weeks for work, but once I get back I'll be putting in an actual 6.8k and also finishing up F2723 as well as doing the amp boards. I can't wait to get it finished and put into regular use!

I can't thank you guys enough for the help, and for the knowledge you've shared in this, and many other threads. What a great community!

 

[TupolevFan]

Great!!! Congrats with a new toy

 

[vigman]

NICE !

 

[TupolevFan]

This is interesting for me. When i used to do a lot of TV repairs back in 90's I noticed one interesting thing. As some of you know i am from Latvia which was former USSR republic. So in the beginning most of my repairs were for the TV manufactured in USSR (Clingon Empire )) They often had sh..ty Electrolytic caps and also some rectangular mica film (was it mica??) caps which were failing miserably. In general quality of electronic components were lower then western counterparts but resistors ..... . I very very rarely saw bad resistors. I remember when repairing my first Western TV ( think it was Philips) It took me 2 days to figure out what was wrong and it was a resistor. For most resistors manufactured in USSR you had to literally abuse it and then hit it with the sledge hummer 5 times ))) for it to fail. I was staring at that open resistor from that TV like it was an alien since it had no signs of overhitting or anything else. Or recently when repairing my my Sansui AU-D7 in a bias circuit several resistors drifted in values and those were not fusible resistors. Now days i see resistor of size 0.125W rated for 0.5W and it makes me wonder. I understand that today's materials can withstand higher temps but i do not want a frying pan. This is why i now opt to military grade RN series (or similar) resistors. At least they have correct size for the wattage and most likely would not drift- just for that i do not mind to pay couple of cents extra

 

[TupolevFan]

This is interesting for me. When i used to do a lot of TV repairs back in 90's I noticed one interesting thing. As some of you know i am from Latvia which was former USSR republic. So in the beginning most of my repairs were for the TV manufactured in USSR (Clingon Empire )) They often had sh..ty Electrolytic caps and also some rectangular mica film (was it mica??) caps which were failing miserably. In general quality of electronic components were lower then western counterparts but resistors ..... . I very very rarely saw bad resistors. I remember when repairing my first Western TV ( think it was Philips) It took me 2 days to figure out what was wrong and it was a resistor. For most resistors manufactured in USSR you had to literally abuse it and then hit it with the sledge hummer 5 times ))) for it to fail. I was staring at that open resistor from that TV like it was an alien since it had no signs of overhitting or anything else. Or recently when repairing my my Sansui AU-D7 in a bias circuit several resistors drifted in values and those were not fusible resistors. Now days i see resistor of size 0.125W rated for 0.5W and it makes me wonder. I understand that today's materials can withstand higher temps but i do not want a frying pan. This is why i now opt to military grade RN series (or similar) resistors. At least they have correct size for the wattage and most likely would not drift- just for that i do not mind to pay couple of cents extra

By the way if anyone interested in those RN series Mouser has much better inventory of those then DigiKey. in Mouser search control just enter "Military resistor(s)"