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Sansui AU-777A: Screwed

jeeem

jeeem

Active Member
OK, this question probably does not require the kind of electronic/audiophile expertise we customarily rely upon from AudioKarma members, but please bear with me.

I just got a long sought-after Sansui 777A that was a little dirty/grimy with a burned out power bulb. No big deal. But I wanted to ultrasonically clean the knobs and polish the face, but this middle defeat knob has a stripped screw and I can't get it to budge. I got the other one (yes, the thing has tiny double screws in each knob), but this one is stuck. I've tried searching the web for ways to remove tiny, stripped, recessed screws, but rubber bands, latex gloves, and WD-40 have got me nowhere.

Which brings me to you. Do folks here have their own tried-and-true ways of dealing with stubbornly immovable screws? Many thanks...

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Hard to tell from the pic the condition of the screw slot.

Is the thread stripped? Or the slot mangled?
 
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If the set screw is brass you can drill it out easily. Otherwise drilling out will be a major challenge. Or try to dremel in a new slot. But I was never able to successfully pull that off... If the knob has two set screws you need not really care about the thread.
 
Apply 'penetrating oil' and let it sit for at least 24 hours - then try again - but it depends on that slot, if one side has snapped off you'll have to drill it out.

You could try heating the screw with a soldering iron, and then let it cool - add penetrating oil and give it another try. OR a hair dryer (not too much!) on the knob but shield the front panel first and then 'freeze spray' on the screw only - then try same process.

Good luck!
 
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roger2 said:
Hard to tell from the pic the condition of the screw slot.

Is the thread stripped? Or the slot mangled?
Click to expand...

The threads are most likely fine. It's the slot in the head that's been damaged. Looks like a previous owner had the same trouble I'm having...
 
If the threads are OK then I agree with the approach suggested by Hyperion.

PB Blaster (sold with automotive products) is, in my experience, better than Liquid Wrench. I would apply a drop or two of PB Blaster then use heating/cooling cycles to expand/contract slightly the metals. The metals are dissimilar so they will expand/contract at slightly different rates, meaning that the PB Blaster will be able to get in there even better than without the heating/cooling, and break loose the threads.

The screwdrivers made for working on eye glasses, come in a set in a small plastic box and are cheap, but those have good crisp blades which could possibly be helpful in grabbing inside the damaged slot.
 
It looks like the screwdriver slot is half broken out.. So any drilling is going to be very tricky and difficult with and uneven surface.
 
rickb119 said:
You might try using a reverse/left handed drill bit. Use a regular bit first, to give the reverse bit something to grab onto.
Click to expand...

UPS just delivered a set of precision titanium left-handed and extractor drill bits. Now it's time to walk the dog and then get to work. Thanks for your help -- and wish me luck!
 
Good luck! Let us know.

If you do happen to mess up the internal treads, you could always re-tap it, even if you had to use a slightly larger size tap.
 
It worked! Thanks again to everybody who pitched in with ideas. My grandpa (a Boeing mechanic for 50 years) always emphasized the importance of having the right tools for the job. My problem is I keep discovering the need for tools I didn't know existed!
 
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