Discussion in 'Exclusively Sansui' started by Bigdrive, Aug 5, 2017.
I'll be interested to see what you have worked out for this item.
All of page 5 makes for great reading, lots of information presented, well done.
The rca connectors on the AU-X1 are supposed to self shorting when nothing is plugged in. This is important i think for the phono rca sockets. When you install new sockets, you can do the same by using shorting plugs in the empty phono rca sockets
Thanks for the encouragement. I will be sure to post pictures of the rca work. I am sure the relay change will fix the resistor problem.
I am doing the mm F-2770 to see why it is low and had a question about transistors. When I did the first three rounds of restore on this amp I just did basic dmm testing in circuit on the transistors. Now that I am looking for a specific problem should I just replace all transistors on that board? Or just the ones with low hfe? Also there is a list of known troublemakers, ie, 2sa726, but on that list is not the 2sa992 which this amp has a lot of. Included in this post of the d357/b527, as you can see, previously these were running HOT, to discolour like that. Now the card never gets above 89f.
Any info would help. I was considering doing only one board and then comparing them. It might be a interesting test
Harold, I was just looking at that! Would you only need the plugs for phono, as they are all shorting except power amp in?
I seen the mod at Amp8 web site while looking at audio porno. This pic is from him.
Correction, I had another look as computer and unit are in different places. Phono 1/2, tuner,tuner/aux, tape1/2 play only and power amp 1/2 in only are shorted. So would all those get shorting plugs?
As i understand only the phono inputs would need shorting plugs, since these can pick-up some interference. But you can try that yourself once you installed the new sockets
While the X1 is apart i am re-reading all X1 posts and noticed that in one of @Kale posts he states for the power supply board..
"Because of that version Power Supply board was without foil capacitors parallel to big 1000uF electrolytic capacitors, I soldered RIFA polypropylene capacitors to bypass those big electrolytic capacitors..."
He never states the value of the caps he addes. My unit also does not have these caps. What value and type are they? RIFA? As i want to add them.
The power protection board F-2781 or the regulated power supply board F-2778?
F-2781 has just one 1000 uf cap.
It's the F-2778. I think the 1000uf is c37,38,43 and c44. Here is a picture as I got the unit and as you can see no parallel caps.
. I want to add them as Kale did and I think all later models had from Sansui. Amp8 site shows before work with them there.
Wondering if .47uf will work such as these.
. I also have 2.2uf both 450v.
Regarding F2775 and the R36 and R37 390ohm resistor what is everyone putting in that spot?
Mine were all OK but I had some trouble adjusting bias on one driver so I just put in 390 1/3 watt carbon film back some time ago, which fixed the problem. Since we know this resistor will drift high and it is acting like a fusible type even though the SM does not indicate that, is the 390ohm 1/3 watt carbon film the best choice?
I used regular 390 ohm 1/2 watt.
Are 1/3 watt still made?
Anyway, sorry for leaving you un-replied as regards those smoothing caps you wish to add to your 2778
regulated power supply board.
My donor X1 uses film caps to smooth caps 19, 20, 21 and 22.
The film caps are 224K code which is .22uF (which is 220 nF which is 220000 pF).
Yes you can still get 1/3 watt but it needs two resistors to get close to the value 330ohm and 47ohm but its still not fusible. What got me back on the subject was the OP post of AU-X1 troubles where he shows a picture of that position and its two fuses. @Hyperion says someone was there doing shitty work, which they defiantly were. Then I go to look at mine and what I can get and I see a problem.
Could it be that Sansui wanted to sacrifice the 1/3 watts in case of trouble?
Forgot to mention, thanks for the info on the caps. I will install them tomorrow.
It is possible, and this is a known strategy for circuit protection, but as the resistors originally installed did not appear to be 'fusible' types I decided they were simply underrated. I think I used ½ watt replacements, and mounted them up on ceramic beads.
When increasing the wattage of resistors, you always need to be mindful of what the circuit designer intended. On that AU-X1 I mentioned, someone had greatly increased the wattage of some resistors unnecessarily, and used 2 in the place of one in one position. And now the hapless owner is faced with semiconductor damage very likely made worse by the fact that the resistors didn't 'give up' as quickly as they should have done. Maybe the writing was on the wall anyway, as it was all original, and he made the critical error of fiddling with the input connections with the amplifier powered up.
Great explanation, that I feel comfortable with putting in the 1/2 watt on the other driver. No way would I play with inputs with power on, I don't even select a different source with power on. It would be like playing with nitro glycerin. To me that's just the cost of doing business.
Just got a new toy. It's a ultrasonic cleaner. Here is a picture of the wafers. Center is detoxit d5 and scrubbing, left is d5 and 1 3 minute clean and right is d5 and 3 3 minute cleaning. It's a miricule. Just to clearify, d5 scrub then put into a bowel of cleaner that came with unit (jewelry). Where was this when I did my push switches? Very happy with results.
Looks real clean.
Could you try it with the old corroded RCA plugs?
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