Comments from my life, family, and projects I enjoy.

Tuesday, August 23, 2011

More of my recent activities

Recently, I have also made some time to work on some of the electronics projects that have been gathering dust.
I recently repaired a Sansui AU710 Integrated Amplifier. This is an export unit and is essentially the same as the US spec. AU717 except the AU710 has a dual voltage power transformers and is derated  by 5 watts for 50Hz operation. These are really nice Direct Coupled amplifiers with dual power supplies. One of the nicest designs from the Japanese stereo craze of the 1970s. They are conservatively rated at 90 watts per channel on the AU717 and 85 watts per channel on the AU710. One issue that is common to any Sansui products from this period is glue rot on the printed circuit boards. Sansui used a brown adhesive to stabilize the larger capacitors on the boards so they would better withstand the shock and vibration of shipping. Unfortunately as the adhesive continued to out-gas and dry to a brittle state, it becomes hydrophilic and begins to absorb moisture from the atmosphere creating galvanic corrosion of the surrounding components.

The good news is the boards in the AU710 are all single sided, so none of the PWB wire traces are affected. I carefully scraped away the offending adhesive and replaced any damaged components. This was required on both power amplifier driver boards and the power supply/protection boards. Once all that was taken care of, the unit was reassembled and tested. After allowing the amp to warm up by playing a cd for about an hour, I set the bias current in the outputs and reattached the cover.

The most recent project on the electronics bench is a MCS-3275 stereo receiver. This particular unit was made by NEC. The black face NEC version is model number AUR 8075.

While not as nice as the Sansui, this is still a formidable unit at 75 watts per channel, plus it is a big fancy silver dial unit that most of us remember from the 1970s. The final PA power transistors were shorted in the left channel. These are obsolete NEC devices; 2SDA588 and 2SB618. I replaced these with ONSemi MJL3281A and MJL1302A. These are much more rugged, but it did require some modification to the heatsinks and the mounting scheme. I also replaced the driver transistors and recapped both boards. If this repair is successful I will then recap the rest of the unit.

Update On My Activities.

Back in June, my assignment with the temp agency came to an end. So, what have I been doing, you might ask? Well I have been keeping myself very busy. Come along and let's have a look at what I do when I am allowed to run amok.
I spent some time working out in the garag....Er...Ugh I mean shop, and built this neat little adjustable box joint jig from plans in a magazine I have been holding on to for about 20 years. Mine was built from whatever stock I had on hand, so it is not as pretty as the varnished maple version in the magazine, but is every bit as functional. I made a test joint on some scrap and was able to stand on it without the joint breaking.

 I have also been able to get some paint on some of the parts from the old DeWalt model GR Radial arm saw I have been restoring. For those just tuning in, this old beast was built in 1948 and swings a 14" blade. The old girl is 3 phase, so I will need to build a rotary phase converter, but not to worry; I will take lots of pics and provide a bunch of details so anyone that wants to play along at home can join the fun.

I have also started building a dust collection system for my smaller radial arm saw. It consist of an angled box that mounts behind the blade. There will be a narrow slot at the rear and a tapered chute where the vacuum will attach. The idea is to keep the vacuum slot at the rear narrow so the flow velocity remains high. Initially this will simply be screwed together without glue so that I may make changes as needed. If this initial design does not work well, I will open up the throat in the back so that gravity can assist with the dust collection.

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About Me

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Midlands of South Carolina, United States
Husband, Father, Quality Engineer, Electronics Professional, and tinkerer. Facinated by old technology and well made old tools. Old iron is good.