AU-717 Rebuild/Upgrade

Just completed rebuilding/upgrading all of the boards. I used the upgrades listed in Leestereos thread on this unit. Time to assemble and dial it all in now

Excellent job!

Thanks Leestereo!
Finishing up the final blocks right now. F-2722 is done. Cleaning the glue of doom off the F-2721. I cut a flat scraper razor blade in 1/2. Fits great and avoids scratches on the boards as a screwdriver would leave. Even softening this glue with Acetone it put up a fight. The others I have done (plenty) never put up a fight like this batch. It appears I may have neglected to order resistors to replace the 150 Ohm fusistors. I had 2 new ones in the parts bins I used on F-2722. May have to place another order tomorrow for F-2721

• ZD01/ZD02 Zener diodes- BZX85C22
• D02 (glue damage) - 1N148
• C02/CO3 100uF/35v
• C11/12 1000uF/63v
• C12- 1uF/50v Elna Silmic-II
• R23/R25 Fusistors-150 Ohm metal films 1/4watt
• Replaced a few corroded resistors from glue damage.
• VR02/VR02/VR03- Bournes Single turn cermet

I agree about the glue used on the AU-717, it does seem particularly tenacious; I used ethyl acetate (e.g., non-acetone nail polish remover) to soften the glue for removal.

I did also notice that if the glue has not been exposed to heat and potentially UV from the top down that it maintains that light brown color and is not corrosive. The corrosive "feature" seems to unleash itself when the glue is that darker brown coffee color. It is much easier to remove when its dark though.

Finished up F-2721 tonight. Thats the last of the boards. I will reassmble it tomorrow and boot it up.

I tested all the outputs and replaced any suspect parts/resistors out of value.
You can see what the glue did to the Base leg of TR01. I was able to clean it and reuse the part it tested on spec.
Pulled and tested the output transistors and cleaned and regreased them with new thermal paste.

You so have this covered.. Nice work !!!

It's also a great library of pictures to show how it should be done.

Success! First click slight glow on the DBT, came out of protection and idled perfect. Centered up the voltages to zero on both channels and 20mV of bias. Bourns pots were really nice here it took all of 3 minutes to setup both channels. Connected the Polk Monitor 10s for a listen. It is a very clean amp, dead silent with max volume and no input. My initial impressions are very good!

Volume pot

Can you clean the volume pot? It seems to be sealed.

super98lsc said:

Finished up F-2721 tonight. Thats the last of the boards. I will reassmble it tomorrow and boot it up.

I tested all the outputs and replaced any suspect parts/resistors out of value.
You can see what the glue did to the Base leg of TR01. I was able to clean it and reuse the part it tested on spec.
Pulled and tested the output transistors and cleaned and regreased them with new thermal paste.

Click to expand...

How long did it take to do all that great redo work?

I tore the whole unit down and removed the caps in about 3 hours. I have a Hakko FR-300 desoldering gun which makes component removal a snap.
I spent about 2 hours per evening on it 2 nights in a row to install all the new parts and upgrades. I'd say overall 7-8 hours but I work slow as its a hobby and I'm just enjoying it. I also spend a good amount of time cleaning and such. Now I'll start recapping my CD-10 which has over 100 caps in it...talk about monotonous.

On cleaning the volume pot.

I believe they are sealed up somewhat but there are holes you can spray into if needed at least there was on my CA-3000. On this AU-717 It wasn't noisy so I left it alone. In fact neither of my AU-717 have pot issues. Spraying these type of pots will wash the grease out and onto the contact and wiper. So only do it if you had to. I'll check again on the case is totally sealed on this one or not. Some have drilled tiny holes to spray in but eh... At own risk there.

Re the volume pot, the 717 is a sealed pot, and I found on one that I had noise trouble with, it was not possible to get the spray into the pot effectively, even after driving holes in eaves section.

There is some info here on the disassembly reassembly process

http://www.audiokarma.org/forums/showthread.php?t=420607

Cheers

John

Final before the cover went on.

Do my 517 now! lol
Awesome job, I wouldn't have the guts to tear mine down like that, but I did manage to clean my vol pot, have to remove the front panel, then a second plate behind vol knob, then you can unscrew vol assembly.
2 screws and nuts hold it together, once open the contacts are right there! quite easy actually

Glad you got the volume knob figured out
The main problem with these units is the glue eating into components and the fuse resistors drifting out. Get that knocked out and unless the unit was in a dirty/high heat environment the caps are likely "good enough" for a while longer, all the ones I checked in mine were still good and the original power caps were already high end Nichicons and tested on spec so for now I left them in. I am leery of Nippon Chemi-Con caps as they seem to fail much much faster than all the other brands.

Good to know super, I needed to clean my vol pot as it was very scratchy, now nice and quiet unless i turn it up of course, lol

The terrible result of this and Leestereo's rebuild threads is that nothing else will seem good enough now. Initially I figured I'd be satisfied to get sound out of my mute 717 and maybe some fresh caps, but not anymore.
Is there someone in northern Los Angeles who can perform the equivalent service? I just learned I'll be traveling down there for a family thing in June.
If not, how about Tacoma/Seattle? (I'll be stopping there enroute home)

I have a good ear and can hear things that many normal people do not. Even with all that said its somewhat debatable as to how much better an amp sounds rebuilt with better parts than it did leaving the factory. I think the bulk of the truly noticeable difference in the sound comes from the fact that we are used to the worn out sound of the 30-40 year old components and when we upgrade, clean, reset to specs the amps sound great. It would be interesting to see if a recapped in spec version vs the modded version has a notable difference in sound using the same room, listening material and speakers. In reality human hearing cannot differentiate between an amp that has 1% THD and .003% THD at the same volume levels. Certainly there are room for improvements in some of the designs such as the pre-amp upgrades done by Stereofun on the AU999 which made a drastic difference in the sound. Just my .02 I love this stuff but at some point we hit the 4k TV vs 2300 dpi deal... 3 ft away the human eye cannot tell the difference, its just marketing hype.

More gains can be had by working on room acoustics, speakers, placement, etc. I can say that even on my small fairly efficient pair of Polk Monitor 10's I use in the lab they have much better/faster/tighter low end using the BA-2000 vs the 2000X receiver to drive them and that is using the 2000x pre-amp either way. Larger transformers, caps, etc better control even at the same volume levels. That stuff is very noticeable.