AU-X701 Renovation (help please)

[BigElCat]

I attempted to adjust my DC offset and have put the AU-X701 into indefinite protection mode.

I started a thread on the DYI forum; I'll link it here.http://www.audiokarma.org/forums/showthread.php?t=468603

I could use some dedicated Sansui advice, specific to this model.

My first step will be to replace the variable resistors for the DC offset. I want to do component replacement one step (or one related sequence at a time), so I'll have a better idea of what I did wrong. I'm trial and error all the way.

I need recommendations for the new offset VR's; KVR1L, KVR1R, KVR2L, and KV2R. I've read that the style that rotate clear around are better. Any comments?

Also, what type of heat sink compound should I use for the Mosfets, and where can I get it?

Thanks.

 

[pete_mac]

Hyperion provided the reference number for the correct Bourns multi-turns in his big 701 thread.

Re: thermal paste, any standard kind will do. There are no mofsets in the 701 AFAIK.

 

[Hyperion]

see my post in your other thread

 

[BigElCat]

Thanks guys! I appreciate your patience. All this info is clear in the other thread. I was walking.
http://www.audiokarma.org/forums/showthread.php?t=407637&page=5
http://www.audiokarma.org/forums/showpost.php?p=5342031&postcount=13

Aren't the Sankens mosfets? The eight gizmos attached to the heat sink...I think they're classified as such (?)

I'm going to start by replacing the 8 trimmers with Bourns 3296Y 25 turn trimmers; 4@ 1k ohm, 2@ 100 ohm, and 2 @ 500 ohm.

I'm going to source some quality caps to replace the 470 uF 50v ones on the amp pcb.

I'm not confident enough in my skills to replace all the electrolytics at once.

The trimmers and the glue monster caps will suffice for round one.

Link to various AU-X701 images: http://www.sansui.us/PGMP_AU-X701.htm

 

[BigElCat]

What voltage and wattage ratings should I order for the Bourns 3296Y trimmers?

 

[pete_mac]

Definitely no mosfets in the 701/901. You need to go higher up the food chain to find mosfets in a Sansui.

From memory, most trimmers are 500mw which is sufficient.

 

[BigElCat]

For the 470 uF caps I'm looking at Nichicon Muse KZs.

The Muse also comes an ES and FG. Apparently the FG is the best (?) but they seem to ship with a minimum quanity of 10.

I've also found some nice looking Elnas.

Do you guys have any recommendations?

 

[pete_mac]

I'd suggest looking at Nichicon PW/HE or Panasonic FC/FM - low ESR, high temperature, long life. These are not signal path caps so there's little to be gained by using boutique caps here IMHO.

I used to be a Panasonic man, but I realised that Nichicon HE can be had for about half the price (or less!) here in Australia, so I now use them as much as possible.

 

[Hyperion]

I'd suggest looking at Nichicon PW/HE or Panasonic FC/FM - low ESR, high temperature, long life. These are not signal path caps so there's little to be gained by using boutique caps here IMHO.

I used to be a Panasonic man, but I realised that Nichicon HE can be had for about half the price (or less!) here in Australia, so I now use them as much as possible.

+1 to all of the above, I use Nichicion HE too, there seem to be more 80v rated values than other ranges. My favourite general purpose electrolytic capacitor is still the Panasonic FC, with the FM a close second.

I also really like Nichicon FG for signal path applications - but also Nichicon KZ have attracted my attention for this application as well.

 

[BigElCat]

Rodger that. Non-signal path, so it's Nichicon HE or Panasonic FC .

+1 to all of the above, I use Nichicion HE too, there seem to be more 80v rated values than other ranges.

Are you saying I can substitute an 80v cap for one that's rated at 50v? That might make finding them easier.

 

[Hyperion]

Rodger that. Non-signal path, so it's Nichicon HE or Panasonic FC .

Are you saying I can substitute an 80v cap for one that's rated at 50v? That might make finding them easier.

No, it was only a reference to the general availability of 80v capacitors used in many other (Sansui) amplifiers and receivers. Many capacitor ranges miss out 80v altogether... 50v, -> 63v, -> 100v ...etc. So you see for my purpose I was trying to avoid using a 100v capacitor where an 80v one is specified, that's one reason why I like the Nichicon HE range.

If the capacitor you need is 50v rated - then that is what you should replace it with, 50v rated electrolytic capacitors are very common.

 

[BigElCat]

I found a source for Nichicon PWs. They are 20mm tall and 12.5 mm diameter. The originals are 35mm tall x 18 mm diameter. Huh...mmm :scratch2:

The boutique caps are the only ones I can find in the original size.

Compact is good, but it seems like an electric reserve (cap) should have physical space.

FYI...my main computer locked up, and my back up PC is acting funny. If the 'BigEl' goes missing, it's a technical malfunction.

 

[BigElCat]

Two Panasonic FCs (470uF 50v) are on their way from Digi-Key. $1.01 each

The 8 Bourns are ordered from Allied Electronics. About $2.50 each with a $5.00 handling charge.

The Panasonic FCs are 25mm tall, 12.5mm diameter. A little closer to the original in size compared to some of the super space savers.

Next will be a partial disassembly with pictures.

:sigh:

 

[BigElCat]

Here's the extent of my glue problem on the F5693 amp board; not bad at all.



The Panasonic FC replacements will be the third phase.

By phase, I mean I'll put the amp board back in and power it up before replacing any other components.

First the Bourns (they shipped today) for the DC Offset adjustment.

Should I start in the middle of the adjustment range, at 12.5 turns?

 

[pete_mac]

Nice... your glue doesn't seem to be anywhere near as bad as mine was!

Regarding the trimmers, check the resistance of the originals with a multimeter and set the new trimmers to the same resistance prior to installation.

 

[BigElCat]

Thanks P_M;

Underneath each of my 8 Sankens I found a clear silica wafer; it appears to be some kind of heat barrier that delays the heat transfer. It looks like they are going to be a PITA to reposition. Any recommendations on this?

Also, is it important that I not have any heat sink compound on the legs of the Sankens? It's going to be tedious slipping the Sankens and the wafers back in without scrapping compound up on the Sanken legs (or leads[?]).

I'm going to do all 8 Bourns, and the 2 caps, in one step. Forget my phases...this too tedious.

 

[pete_mac]

I didn't worry about re-doing the thermal compound on my 701. The original stuff is in good condition.

The mica insulator electrically isolates the transistor from the heatsink. If you do reapply the thermal compound, you can apply a thin layer to the rear of the transistor first, then position the mica, then apply another layer on top of the mica. This should keep the mica positioned nicely.

Wipe any excess compound off the transistor legs etc. Hopefully you can avoid getting any compound on the legs in the first place.

Good luck!

 

[BigElCat]

Phase 1 is finished and I'm waiting for the delivery of heat sink compound.

I went ahead did caps 51 and 52, as well as, the four DC offset Bourns:


Here's a pic comparing the original 470uF caps to the new Panasonic FCs:

Good bye glue.

The new ones are about 35% the physical size of the originals. Is this because of technological progress?

 

[BigElCat]

Warning: Disturbing Images

Now for the bad news.

Out of 16 solder joints; 8 are good and 4 are marginally acceptable. The remaining 4 range from questionable to hideous. I tried to redo them. I used a plunge style de-solder tool that caused much of my problem. The best solding iron I have for PCBs is 25w Weller pencil.

Here's the worst of the bad:






I need to study on trace repair, and get some better equipment. I need to get a Freznel lens to compensate for poor vision. This damage is why I don't want to go any further until after I give it a listen. I hope I can't hear this.

 

[BigElCat]

I have a Hakko 888 station and a magnifying lens helmet on its way. I won't have any more excuses for bad solder joints.

I have the AU-X701 reassembled, and was able to set the Hot-Cold bias. I haven't been able to set the Cold-Earth Bias; I'm not getting any reading at the test points. I've bumped another relevant thread to the top of this forum; I'll link it here:

http://www.audiokarma.org/forums/showthread.php?t=418341&page=2

Any help would be appreciated.

I can't get it out of protection mode.