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Noah Fect
User Rank
Iron
Re: what type of failure?
Noah Fect   11/1/2012 3:23:00 PM
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Good call on the pullup resistor, but you didn't change the output stage to class A.  You changed it from CMOS to NMOS. :)

Critic
User Rank
Platinum
Repair
Critic   10/24/2012 2:38:59 PM
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This would be called a "repair," rather than a "rework," right?

Fix-it-or-not
User Rank
Iron
Re: what type of failure?
Fix-it-or-not   10/24/2012 5:07:20 AM
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I like the way you think!  I have a pile of older equipment, most of it works, the rest is still "in progress".

This brought to mind a Sony amplifier I bought surplus 30 years ago.  Until this year, I never had the thing work!  Before I bought it, many others had tried and failed to get the felt channel to work.  I know this because an aquantance of mine had tried repairing it when he was a tech at the university where I purchased it from. 

Over the years, I would pull this out and see if I could get any life from it.  The problem ended up being the bias diode that was secured to the heatsink.  Although it tested fine with an ohm meter, everything pointed to this component.  I ended up replacing this diode with a red led and a 1N4148, connected in series as I needed this potential drop to match the original diode, which has long since been discontinued.  I am sure that the thermal characteristics of this arrangement do not match the original, but the amp sounds great, and matches the right channel when bench tested.

Some times ingenuity goes a long way, especially with vintage equipment!

Steve Lindberg
User Rank
Iron
Re: what type of failure?
Steve Lindberg   10/23/2012 1:37:08 PM
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I should clarify that the 475 was my part of my personal collection.

I rescued it from our local surplus shop R5D3. I paid $150 for it.

Steve

 

Tim
User Rank
Platinum
Management Praise
Tim   10/22/2012 7:08:28 PM
NO RATINGS
The management response to a problem solved and equipment now working is priceless basically stating that the way you did it did not solve the problem.  That is a big pile of management.

naperlou
User Rank
Blogger
what type of failure?
naperlou   10/22/2012 10:49:38 AM
NO RATINGS
Steve, I can see why you did not pursue the discussion with your manager.  If you had fixed a design flaw in the scope it would have called into question all their other purchases.  This might have been a problem when using the equipment to verify designs.



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