SX-750 project - re-cap recap

ronh95

Member
In April, I posted about picking up an SX-750 that I'd planned to refurb and give to my son as a college grad present. Well, after getting sidetracked with house projects in preparation for the graduation party, my timeline slipped and I'm just now completing the project. I know I like to read about such projects so I thought I'd follow up. (previous thread http://www.audiokarma.org/forums/showthread.php?t=653119)

The unit was in decent shape, faceplate/knobs were dirty, but fairly clean, however the vinyl woodgrain was a mess, peeling/missing portions. I ended up veneering the case w/paper backed walnut veneer and used General Finishes satin Oil and Poly finish (no stain - 4 coats wiped on w/a t-shirt). I'd read about the finish on a homebuilt speaker forum and was very pleased with the product. Easy to apply and excellent results without looking like it was coated in plastic. Next, I did a complete re-lamp with parts sourced from our friend djwojo.

My order from Mouser arrived weeks ago, but I failed to check it against the BOM requirements. I went to begin the re-cap last week and realized all the 100mf caps had failed to make my order (my fault NOT Mousers!).

I had planned to work one board at a time, test on the DBT, then full power, then move on to the next board. Since the missing parts impacted virtually every board except the power supply (1 cap and a bunch of diodes that I had), and wanting to maximize the return on my extended holiday weekend here, I defied logic and convention and replaced all caps on all boards at once. I saved the DBT testing for last and I was extremely fortunate in that there were zero faults! I was sweating it, I can tell you. I would NOT recommend this approach. Just too many parts to have not screwed something up, but I did go back and verify continuity in areas where a pad lifted, also polarity/values, etc.

I set the idle current and finally hooked up to speakers, a turntable, antenna and iPod dock. All modes worked and she sounded great! The unit functioned and sounded good before the re-cap, but it showed signs of pretty heavy use so it provides some piece of mind. Also, though I ordered all the transistors, I only replaced the diodes on the power supply (-099?) board so far. I will likely listen to it for a few weeks and then go back in.

I'll try to attach a few pics now and check back later w/some pitfalls/caveats for others that I ran into. Can't leave though, without saying a big 'thank you!' to MarktheFixer, Watthour, BobHelms and others who have shared their wisdom and experience with me directly and through other helpful threads. What a great community here! = )
 

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Good work getting everything in correctly the first time.

Incidentally, that case looks GREAT. I hope the corner blocks were not too difficult to fit after applying the veneer. I know they are tight in their original form, and adding a little to each surface would make it even tighter.
 
Thank you Watthour! The blocks did grow a little in width and height, a double and single veneer thickness respectively, but since the surface where they mate with the case wasn't done they didn't grow in depth where they could have possibly interfered with the case. That rear facing surface was unfaced from the factory so I left it alone.

I actually bought a nice piece of 3/4" S4S solid walnut stock to fab new corner blocks from, but haven't had time to make them yet. That will involve removing a mountain of crap from the tablesaw so it can be wheeled out for use. A daunting task... =)
 
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