technics SA 5070

stoveguyyJune 7, 2012

older technics receiver. speaker output is not working. i hooked it up to powered sub using the line level outputs from the tape loop. fm tuner section works. picks up signal fine. sub has built in amp. gain and crossover settings. i adjusted gain and bass output is fine. i did not try the headphone jack to see if that works. the IC is stk 043 105. i see many stk 043 chips online for $15. says they are 20W approx. think a chip swap might fix it?

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yosemitebill

Your description is pretty typical if I roll back to the 80's. The headphone output will usually sound OK but with a little bit of distortion - the rest of what you describe is at pre-amp line level stages and is not affected.

The STK packages usually did not have much resilience to speaker output shorts - just fried them.

Replace it, most likely the problem, but DO NOT do any speaker connections with the unit turned on and ALWAYS check for any frayed, just "slightly touching" connections at both the amp and speaker end connectors.

Panasonic use to make some very nice equipment in their Technics line - they had a lot of warmth not found today in our digitally sourced world.

    Bookmark   June 7, 2012 at 10:21PM
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stoveguyy

i just got the sub and needed a source to make it work. the technics has been in a closet for years. would be nice to fix it but don't want to spend much. maybe bad caps on the power supply? i have other plans for sub.

    Bookmark   June 8, 2012 at 8:29AM
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stoveguyy

power supply is working. the display uses a reflector with several bulbs. that circuit is getting 12v. blu/brn wires from xformer. the orange wire is putting out 18v or so.

    Bookmark   June 8, 2012 at 12:23PM
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yosemitebill

So... if you can find an STK043 online - go for it!

Like you said, the electrolytic caps in the power supply might end up being dried out, but they're dirt cheap to replace.

Have fun and make sure you pick up a can of control/switch cleaner/lube!

    Bookmark   June 8, 2012 at 7:12PM
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stoveguyy

my IC says stk-043-105. the ones online say stk043 only. any idea what the -105 refers too?

    Bookmark   June 9, 2012 at 11:10AM
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yosemitebill

The STK043 has a max case temperature rating of 90 degrees C. The STK043-105 has a max rating of 150 degrees C.

The -105 would obviously be preferable since that's what's in there, however, if you can't find the -105, the other version is electrically compatible - just don't crank-it and make sure you use 8 ohm speakers.

    Bookmark   June 9, 2012 at 12:08PM
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stoveguyy

got my new ic.

    Bookmark   June 17, 2012 at 2:42PM
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yosemitebill

Alright - looking good!

Don't forget generous heat sink compound on the backside of the IC and double check for solder bridges with a magnifying glass and "dental pick" after you install it - and before you plug it in.

    Bookmark   June 18, 2012 at 10:36PM
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stoveguyy

i took a pic of the solder joints before i started.

    Bookmark   June 22, 2012 at 8:03AM
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