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Thread: Technics SX PR603M Problem

  1. #1
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    Technics SX PR603M Problem

    Hello,

    I am a new user, but from reading the forums have seen some extremely good advice offered on here so I hope somebody can help me understand this problem.

    I have recently purchased the Technics SX PR603M, second hand. When I tested it there was no problem but when I got it home things changed.

    When first powered up everything appears to be fine (all LEDs come on, the screen loads up, sound is produced). However, after around 1 minute all of the LEDs switch off apart from the main power LED and floppy drive LED, the display goes off with only the backlight on (blank blue flashing screen), and no sound is produced. If I leave it switched on everything returns intermittantly until a key or button is pressed then it cuts out again.

    As the key board functions perfectly for the short period of time it works I think it may be a problem with the internal power supply, but this is only a guess.

    Is anyone familiar with this model/fault, or can anyone help at all???

    Thanks

  2. #2
    Vice Admiral Virtuoso wljmrbill's Avatar
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    I would suggest going to their web site and looking up problem or contact them for a technician that can repair it for you. Sounds like a blown or weak circuit board and well maybe in the power unit. Good Luck,
    ....To play only what is written is the domain of science. To realize what is not written is the domain of art."
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  3. #3
    Administrator Krummhorn's Avatar
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    The only thing that changed between the trial and turning it on at home was that is was physically "moved." Something may have gotten jostled, a connection, a circuit board came loose ... when things warm up, electrical connections have a tendency to expand ... if some connection is "hanging on by a thread", chances when it warms up, the connection is lost.

    The inner workings of these things is best left to a professional ... someone who knows what they are doing. Amateur electronics repair jobs usually wind up zapping something else unrelated to the original problem, making things worse, and in turn, costing twice as much to fix.

    If you are handy in electronics, get yourself the schematics for this instrument before you attempt any repair.
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  4. #4
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    Thanks

    Thanks for the comments so far.

    I completely get the point about it being moved, but when I tested it it was for a short period and it was still ever so slightly slow to start up, and when it did start up it then reset quickly but then worked so, at the time, I presumed this was due to it being unused for a while.

    I think that it could definately be that when the electricity begins to pass through it a connection breaks, or when it was moved it loosened a connection but WHERE the connections breaks could surely have hundreds of possibilities?

    I am technical enough to be able to change or repair circuits, but finding the faulty circuit will prove the problem.

    Any further nudges in the right direction would still be great. Has anyone ever opened one of these up or fixed a similar problem on a Technics instrument that may bare some relevance.

    Thanks again.

  5. #5
    Administrator Krummhorn's Avatar
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    Quote Originally Posted by Jonathan Bennett View Post
    Thanks for the comments so far.

    I completely get the point about it being moved, but when I tested it it was for a short period and it was still ever so slightly slow to start up, and when it did start up it then reset quickly but then worked so, at the time, I presumed this was due to it being unused for a while.
    Could be something as simple as the on/off switch ... a dirty contact perhaps. Doesn't take much - a little piece of lint in a switch can wreak havok.

    Quote Originally Posted by Jonathan
    I think that it could definately be that when the electricity begins to pass through it a connection breaks, or when it was moved it loosened a connection but WHERE the connections breaks could surely have hundreds of possibilities?
    From my years of experience working on digital organs in years past, this certainly sounds like a switching problem.

    Quote Originally Posted by Jonathan
    I am technical enough to be able to change or repair circuits, but finding the faulty circuit will prove the problem.
    If you can, open the case ... look for any obvious loose connections. The one thing you won't be able to "see" is a cold solder joint ... an electrical connection where the solder wasn't heated sufficiently enough to flow properly, thereby making the connection so-so.

    With the unit unplugged, you can check out many connections with a VOM for continuity.

    Quote Originally Posted by Jonathan
    Any further nudges in the right direction would still be great. Has anyone ever opened one of these up or fixed a similar problem on a Technics instrument that may bare some relevance.

    Thanks again.
    Kh ~~.
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  6. #6
    Vice Admiral Virtuoso Dorsetmike's Avatar
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    If you do risk taking the covers off, disconnect from the power supply first , then check all the connectors, if there are dirty contacts you can sometimes improve things by unplugging then reconnecting a couple of times, the friction may be enough to improve the contact; if the printed circuit boards have "edge connectors" i.e the contacts are actually printed on the PCB, then rubbing them with an ordinary pencil eraser can often do the trick, don't use any abrasive like sandpaper which might damage the contacts.

    Look for signs of obvious overheating of components. If by any chance you live anywhere near the Poole/Bournemouth area of England send me a PM.
    Cheers MIKE.

    How many roads must a man walk down ... ... before he admits he's lost?

  7. #7
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    Thankyou.

    Krummhorn, by a 'switching problem' do you mean a problem with the power switch like you wrote in your responce?

    Mike, great advice thanks. Unfortunately I am up in Newcastle so not too close Poole but I am going to examine the inners of the unit tonight.

    Thanks so far. I will let you know the outcome tomorrow...

  8. #8
    Administrator Krummhorn's Avatar
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    Hi Jonathan,

    Yes ... I was making reference to the main power switch. Here, across the pond, an old technicians trick is to slide a fairly new dollar bill back and forth between the switch contact points.

    Before that, we used Carbon Tetrachloride, but that was banned many years ago ... I guess too many technicians were getting stoned on the chemical odor

    I'm not sure the British paper note would have the same effect.
    Kh ~~.
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  9. #9
    Vice Admiral Virtuoso Dorsetmike's Avatar
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    You could try an email to

    sales@wdgreenhill.com

    quoting model number asking for user and/or service manual, I got one for a Farfisa K/B last week, about £12.50 with P&P.

    They don't have your model listed on their site, but neither was my Farfisa, they found one within a couple of days though.
    Cheers MIKE.

    How many roads must a man walk down ... ... before he admits he's lost?

  10. #10
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    Right.

    I opened the unit up and the circuit board with the ac input on it was a mess. Three of the components were completely fused together with what looked like circuit board glue, or melted circuit board. I cleaned the subsance off and seperated the components and though this would be it, i'm back in business...

    I powered it back up and it lasted a little longer than usual but then cut out again - that made me think that it maybe wasnt the damaged circuit board that was the problem.

    At my wits end, I put some pressure on one of the small micro chips on the main circuit board in the centre of the unit - which looks like the equivelant of the motherboard - and it kicked back into life. So by touching this chip it switched it on.

    However, I am not convinced that the chip I put the pressure on was the problem. Once I have got past the initial reboots, which last for about 5 minuites, it all works perfectly for hours, no problems. This suggests to me that the capacitor may be at fault and is taking a little time to create enough energy to sustain a constant flow of DC power. But then again what are the chances of the micro chip being fault and me putting pressure on it resolving the problem? surely slim.

    Any thoughts on any of this confused mess?

  11. #11
    Administrator Krummhorn's Avatar
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    The fused components ... any strange odor like that of a burned resistor apparent there? The damaged circuit board could be part of the problem ... or it was a temporary "fix" of the previous owner. Lots of circuit boards are covered in a clear acrylic to prevent corrosion and moisture from damaging the components. Perhaps the prior users fix involved changing out one of those components. That acrylic stuff, when heated up from a soldering iron, never flows back to its original state.

    There are "traces" in multi-layer circuit boards, as you know ... any one of those traces in any one of 4 or 5 layers could be at fault. Possibly putting pressure on the IC "makes" the connection come alive ... could also be a cold solder joint, where the initial soldered connection was not heated sufficiently enough to properly flow and make the connection(s) solid.

    Your theory of it possibly being a cap does make sense ... possibly in the main power supply or amplifier.
    Kh ~~.
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  12. #12
    Vice Admiral Virtuoso Dorsetmike's Avatar
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    Was the chip soldered in or in a socket? It's not unknown for the sockets to make a poor connection or the chip could have been a bit loose in the socket so pushing on it could have reseated it in the socket. If it's soldered in then could be a poor solder joint, soldering on printed circuit boards is not for the faint hearted or fumble fingered, you need a soldering iron with a fine point tip and a steady hand.

    Another possibility is a crack in one of the printed circuit tracks, pressure on the chip could have flexed the PCB a bit and remade connection, again a delicate job with a soldering iron for a permanent repair.

    Any of these possibilities could cause your problem, as it warms up after switch on expansion of the board could cause the loss of connection.

    Nowadays though the usual action by a service engineer would be to change the complete circuit board, which may be cost effective for the repair company in terms of time and labour and minimal staff training, but not for the customer!
    Cheers MIKE.

    How many roads must a man walk down ... ... before he admits he's lost?

  13. #13
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    The circuit board did have a stange odor - like burnt electronics.

    The 3 fused components were a capacitor, an red oblong shaped component, and a metal loop with red and white wires wrapped round it - these were all on the board for the first point of entry for the power. I dont see how that could have been a fix for anything, it looked dangerous. It is in such good condition that i'm starting to think it may have been a factory mess up.

    The point about layered circuits makes perfect sense and it would be easy and harmless to replace the chip, but If it works for hours once it has passed the startup teething problems this seems to eliminate the chip problem.

    What if the cap on the input power board isnt initially producing enough DC for the chip that I put pressure on so while there is this lack of power the chip needs encouagement by me putting pressure on it, but once the cap gets going the chip then has sufficient DC to fend for itself?

  14. #14
    Vice Admiral Virtuoso Dorsetmike's Avatar
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    Layered boards are usualy only found on larger and more complex equipment, keyboards are quite simple electronics by comparison.

    I would doubt if it's a capacitor problem. Have you tried poking about around the PCB using something non metallic, a toothpick or some small piece of plastic to see if there is any reaction, does the fault return, or can you hear any click or noise from the speakers? You may be able to localise the fault area and then examine the suspect area closely for possible damage.

    Or as we used to say when training maintenance engineers, we'll teach you just where to kick it, and also how hard to kick it.
    Cheers MIKE.

    How many roads must a man walk down ... ... before he admits he's lost?

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