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Old 5th February 2013, 01:41 PM   #1
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Default Sony AX380 and JX380 issues

Hi, new kid here, well... if you can call a 68 year old a kid

I have a Sony home stereo that has been sitting for about 6 years. I hooked everything up the other day and discovered a couple issues that you guys may be able to give me a little insight into. I am posting this before removing the covers to maybe get a clue as what might be the problem. An internet search for service info didn't turn up anything that was helpful.

The tuner (ST-JX380) will not hold the presets. If it's powered down it forgets the channel settings. Anyone know if it might have a back up battery or perhaps a super cap that is suppose to maintain the memory?

The Amp (TA-AX380) works OK but the volume control isn't working from the remote. I have the original remote so the codes shouldn't be an issue. Guessing it has a motor that turns the control and am hoping it might just be a bad coupler or something mechanical. I might find time to take the cover off later today and see if anything jumps out at me.

Would sure appreciate any help or insight you might be willing to share on these two units.

BTW: Spent most of my working life fixing two-way radios for Motorola, have a pretty good understanding of electronics and trouble shooting but feel blind without a schematic.
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Old 5th February 2013, 03:30 PM   #2
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Think I found one of the culprits. Believe this is a supercap found on the front pannel board of the tuner.

Looks to me like it's a 0.22F 5 volt cap but this is the first time I have had to replace one so need to be sure I'm reading it corectly.
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Old 5th February 2013, 06:46 PM   #3
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That's a backup cap and could well be faulty. It should read around 5 volts (max) across it when on and obviously should retain that when off. If you check it remember your DVM will discharge it slowly, you'll see the voltage drop.

They do go duff. A quick test can be just to replace it with a 100uf cap. That should keep the memory alive for many minutes + as a test.

Before getting heavy with the volume control, first check the RC is really transmitting. Point it at a digital camera or web cam and make sure you can see the IR diode pulsing. Try other remotes too, so you see what it should look like.
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Old 5th February 2013, 06:52 PM   #4
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Remember to measure the voltage with the tuner switched off, and even disconnected from mains at least an hour before measuring.
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Old 5th February 2013, 08:48 PM   #5
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Guess I should have stated all the other functions on the remote work.

Have the poor thing spread all over the living room. The supercap is bad, looks to be open from my tests. Will try to locate a replacement. That was the easy one.

This is going to be the hard one. Pulled the cover off the amp and have plus and minus 5 volts to the volume control motor when the remote is activated but motor doesn't run. Bad motor and looks like it would be chore to try to replace without buying the whole assembly.

Anyone know where to buy Sony parts and what kind of number I should look for. The board the motor is soldered to has a couple numbers on it but not sure if one of them would be a good # to order with.
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Old 6th February 2013, 07:42 AM   #6
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So the caps sorted

Just to be clear on the motor, you are measuring the voltage across the motor itself, and not from ground to each motor lead. It just avoids confusion because the motor will be fed from an "H bridge" driver and so could see any (but the same) voltage on both sides. If the motor has voltage across it and its not turning then yes, motor duff.

I wouldn't give up that easily on the motor though Nothing lost in seeing if it comes apart and/or responds to a quick "zap" of voltage (disconnect it first of course).
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Old 6th February 2013, 09:43 AM   #7
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Ya I measured across the motor, was thinking lastnight could be the brushes are dirty or coroded from sitting for years. It's worm drive and the gearing is inside a metal box making it difficult to turn the motor shaft by hand.

I have removed the assembly from the amp and when it warms up later today I'll take it out to my shop and see what I can do with it.

Thanks for the tips..
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Old 7th February 2013, 09:26 AM   #8
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A little update..

Yesterday I hooked the volume motor to my bench power supply and slowly increased the voltage. At about 10 volts it started running. Reduced the voltage to 5 volts and checked it both directions. Horary it worked.. Installed it back in amp and it's working great. One issue out of the way

Have the cap for the tuner on order from Mouser which should solve the presets issue with the tuner. I believe we are well on the way to having this old system working as it did when it was new. It sure does sound good.

Thanks for the help.
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Old 7th February 2013, 10:31 AM   #9
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Thats good to hear. A bit of voltage works wonders (in the right place )
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Old 22nd July 2013, 07:42 AM   #10
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Hey guys, I have the same exact radio and amp as the OP.

The digital camera trick for testing a remote control is REALLY NEAT* and I used it to find that my power button, volume buttons, and d. select? button aren't working while the rest are (with the muting button being a little inconsistent).

I don't like to waste parts that can be fixed so what's the best way to clean the contacts on the buttons that don't appear to be working? (Is there a way to safely open up a remote like this without damaging it? I've fixed cell phones before and I used a plastic 'safe pry' tool to undo the clips, would it be something like that?)

*seriously, you guys have my respect for knowing something like this.
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