Sansui AU-717

[wtp]

HI all, able to shed some tips/advices for the above amp of mine tat has been wif me for quite a while?

I do understand tat the AU-717 was from the Sansui 07 series of amps, it was classified as the smaller bro to it counterpart AU-919.

All the while it has been working fine wif minor issue, the problem was from cold start to power on n i always had the habit of switching the speaker knob from selection speaker A to off wenever i tend to off the amp after some leisure listening n vice versa. Volume,Loudness,Subsonic n Tone will also be in off position if i happen to fiddle wif it but usually i hardly touch it. It is consider as a correct/proper procedure to switch off the amp or is there any other better alternative than this?

So my issue lies in wenever i on the amp, turn on to speaker A from off position, i always experience some hiss/shassy soft sound from my L/R ch speakers. So inorder to eliminate this disturbance, i switch back to off position on the speaker selection. Aft a preheat/warming of 10/15min or so, i switch back to speaker A n gosh the hiss/shassy sound is gone.

Recently i pick up the courage to replace the E caps thoughout the output drive n power section. Of cos i did a lot of reading from various site etc... AK, Cdkands or audio review b4 i attempt the task. Those nasty glue on the pcb tat causes corrosion to various parts has now been cleaned n remove by solvent thinner. All caps has been replaced wif Nichicon/Elna caps of same value/voltage(105 degree celcius) not consider audio grade type cos i was on a budget roll. I did best of wat i could n i do admit its power section is one of the hardest part to rectify. Aft the cap change, the hiss sound still persist duing the initial switching on of amp.

My personal background is basically i know nothing bout electronics, but i do know desoldering/soldering skills of parts n simple measurement of caps n voltage.

Any generous feedback wld be greatly welcome, lastly tks

[Alec124c41]

I have had to replace the speaker protection relays in a couple of amps. The points/contacts oxidize and/or pit.

Cheers,
Alec

[duficity]

Maybe the use of proper English would allow one to understand and respond

[rhomanski]

There are two circuit boards with 2sa726 transistors. F-2723 and F-2720 the equalizer circuit board and the tone control circuit board. One is the board in the front of the unit and the other is the vertical board on the side of the unit. These transistors should be replaced with KSA992FBU transistors. I also replace all the diodes. The VD-1212 diodes should be replaced with two 1N4148TA diodes in series. I solder them together side by side with the bands opposite and cover in heat shrink. So that they make a tall component like a capacitor.
I usually replace the relay with an Omron relay and the transistor that drives it. You also have to replace the fusible resistors with flameproof resistors of the same value. Replace the trimmer resistors on the driver boards with Bourns trimmers. The heat sink grease should be replaced on all transistors that are heat-sinked. Also clean all the pots and switches with CAIG Deoxit D5 repeatedly. This usually fixes all the problems with the amp. Although it may not in all cases.

Regards,

Ron.

[wtp]

Well tks for the highlight, i guess the above seems tedious due to my lack of electronic background

Any chance do i nd to change out the 4 main big cap(15000uf/63wv) since i already does for the driver/power board?

Parts changed
F-2721/2722(output driver)
470uf/63v, 33uf/25v, 1uf/50v(E cap)
473k/100v, 334k/100v, 182j/100v(Mylar cap)

F-2663(Power supply)
470uf/16v, 470uf/10v, 220uf/63v, 220uf/6.3v, 100uf/63v, 100uf/35v, 47uf/50v, 33uf/50v, 4.7uf/50v, 0.47uf/50v(E cap)
473k/50v, 334k/100v, 273k/50v(Mylar cap)

[rhomanski]

I always change every electrolytic capacitor with a new one, including the four main ones. I use Panasonic THA series for those in an 80 Volt size. They are shorter than the originals but the same diameter. I don't touch the square green or orange ones unless they are damaged. I did find one once in a different unit that was split on the end so I did replace that one. Also the clear plastic ones are very sensitive to heat. Don't even touch up the solder on one of them. One person said he marks them with a pen when he resolders the board. Just to make sure he doesn't accidentally resolder one and take the chance of ruining it.

When you clean up the glue on the three boards, you should replace every component touched by the glue. That usually includes some diodes and a few resistors. What I usually do is strip the chassis down to just the transformers and the regulator board and main caps. I remove everything else. It makes it easier to work on everything else. Take plenty of pictures showing how everything goes back together.

Regards,

Ron.

[wtp]

Dismantle of the output driver board F-2721/2722 is relative straight forward, remove the 8 self-tapping screw on top n below wire sockets of various colours to retrieve it. I do copy down the wiring config in the ease of assembly part, but also the driver board itself does indicate the colours of sockets as well.

The real headache was the power supply board F-2663, for this i open up those plastic retainers tat bundle the wires together below. Loosen up screws of the 4 big charging caps(15000uf/63wv), output board n backcover of spk/rca post out.
Bit by bit, wif caps n supply board out to an extent i able to wk on it. The board was still on chassis wif all the wiring intact.

Desoldering of all E-caps n Mylar caps. Cleaned up glue using thinner solvent, scrap though it using ice-cream stick. Solder back new similar specs of caps.

Wen everything was assembled, the initial powering up was a gamble. If it shall fail, i probably lose it. If it wk n cure the issue, i will feel contented.

But somehow the issue still remains, gd news is the amp still functioning. A kind of mixed feeling though. Well probably i giv it a try again by changing out the relay as the problem lies in after 8s or so wen the relay clicks, there came the hiss sound on both L/R speaker aft the spk selector switch is being selected.

[wtp]

F-2721 has 3 pcs of IS2473D diode at D01,D02 & D04 similar to F-2722

Wat shd be a gd subsitute for it?

Tks n regard

[rhomanski]

I use the 1n4148TA to replace those diodes.

Regards,

Ron.

[wtp]

There are two circuit boards with 2sa726 transistors. F-2723 and F-2720 the equalizer circuit board and the tone control circuit board. One is the board in the front of the unit and the other is the vertical board on the side of the unit. These transistors should be replaced with KSA992FBU transistors. I also replace all the diodes. The VD-1212 diodes should be replaced with two 1N4148TA diodes in series. I solder them together side by side with the bands opposite and cover in heat shrink. So that they make a tall component like a capacitor.
I usually replace the relay with an Omron relay and the transistor that drives it. You also have to replace the fusible resistors with flameproof resistors of the same value. Replace the trimmer resistors on the driver boards with Bourns trimmers. The heat sink grease should be replaced on all transistors that are heat-sinked. Also clean all the pots and switches with CAIG Deoxit D5 repeatedly. This usually fixes all the problems with the amp. Although it may not in all cases.

Regards,

Ron.

Relay - Omron MY4-02-24VDC
D01,D02 & D04 - 1N4148TA
R23 & R25 - 150ohm fuse resistor
2SA726 - KSA992FBU

Just some clairfy
Wat r those transistors to drive the relay? A good subsitute for them?

Wat value for the trimmers for V01,V02 & V03 to be replace by Bourns?

Regarding bout the VD1212 diodes to be replace by 1N4148TA in series, able to post some picture of the configuration?

Yr help is much appreciated, tks Bro rhomanski

[rhomanski]

Okey Dokey,
That is the correct relay, except you will have to clip off two of the pins. They are not used anyway and the board has no hole for them. It will give you two paths for the signal for each channel. The original only has one path for each channel. It gives better reliability because if one path fails from carbon scoring the other will still work and you will not know the difference.
Those are the diodes I use to replace the 1S2473D as well as the 1S2471 in other amps. For the 10d2 diodes, I use 1n5393S to replace them. For the RD-13E zener diodes I use BZX79C13. You should replace the RD-13E while you are in there. Zener diodes are not known for their reliability over the years.
All fusible resistors should be replaced. It's best to use flameproof. They have a coating that will not allow them to burn should there be a short and they get hot. The fusible resistors were supposed to blow first and prevent further damage. As it turned out they blew after the damage was done. So they served no purpose and will rise in resistance over the years until they finally go open. Sansui seems to have switched to a different kind in the last units made that is not as bad as the first ones. Still I replace them. Replace R23 and R25 on F-2721 and F-2722. They are 150 ohm. Replace R47, 48, 49, and 50 on the F-2723 board. They are 82 ohm. Replace R37, 38, 39, and 40 on the F-2720 board. They are also 82 ohm.
Yes, replace the 2SA726 transistors with KSA992FBU. The pinouts for the two are opposite, so put the KSA992FBU in backwards in relation to how the original transistors are installed.
The relay is run by TR603 on the F-2663 board. It is a 2SC945. It is still available from MCM electronics I believe. Or can be replaced with a 2SC15090S-ND. The pinouts are the same so the orientation is the same. A direct swap. You could also use a BC237B, but the legs would have to be overlapped because of the way the pinout is.
I usually replace D608 because it is the protection diode for the reverse currant from the collapsing relay coil field. I use a 1N4004 for that. Easily found and fairly robust diode.
The trimmers are 100 ohm, 1K ohm and 2.2K ohm. I use the 3386 model. Either F or G whichever is side adjust I don't remember right off hand. The other style is top adjust.
I don't have a means of posting pictures right now. But just lay two diodes side by side. One with the band away from you, one with the band towards you. Bend the two leads that are away from you toward each other and solder them together. Cut off the excess length down to the solder. Now cut the lead near you on the banded end short so you will know which is the negative lead and cover the thing with heat shrink. Remove the VD-1212 from the board and install your replacement with the short lead, that you cut, at the hole the arrow points at.
Hope this clarifies it all for you. If you need more help just ask.

Regards,

Ron.

[wtp]

Alright i gettin a picture this time round

Jus an update

1)Omron relay top part stated MY4N 24VDC, below shows 14 pins, is this the correct one?

2)RD-13E - Able to use(ST 13v) cos i unable to find BZX79C13?

3)All the resistors i obtain was 1/2 watt, although certain web info stated R23/25 to 1/4 watt fuse resistors? Original resistors in board 1/4 or 1/2 watt cos i only change out those being affected by the glue beside R23/25 i change all 4 pcs on F-2721/2722?

4)V01(100ohm) V02(1Kohm) V03(2.2Kohm)?

[wtp]

Additional info on Omron relay

Side panel stated Contact:5A 240VAC/5A 28VDC Coil:24VDC

[wtp]

Ok i getting some hints from studying the schemetic diagram

V01 - 100ohm
V02 - 2.2kohm
V03 - 1kohm
I try to get the model 3386 from Bourn

As stated by the resistors value, IMO if i nt wrong, all shd be in 1/4 watt unless those specially stated eg.R09 2.2k(2) = 2watt?