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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details. |
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8th Feb 2019, 7:22 pm | #1 |
Retired Dormant Member
Join Date: Feb 2019
Location: Burnley, Lancashire, UK.
Posts: 1
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Technics PR305
Hi there,
I have a dead technics pr305 in my living room wanting some tlc to get it working again. No lights what so ever on the control panel but the power led on the frond of the piano comes on. It has 15v at the test point on the main board, but trying to find the 5v is proving a pain. Also is it possible that the reset is being shorted to stop it powering up (got power led on on front of piano) and if so what is the reset line voltage ment to be and is it just a pulse or continual signal to keep the cpu up? Any other ideas would be greatly received too to check using just a digital multimeter. Thanks. |
15th Feb 2019, 11:32 am | #2 |
Rest in Peace
Join Date: Sep 2010
Location: Ripley, Derbyshire, UK.
Posts: 785
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Re: Technics PR305
It's 20+ years since I worked on one of these, but I recall problems with the solderring of the power regulators causing your symptoms.
If the +5v supply is missing, the whole circuit will shut down. Sadly, all the manuals I had for Technics products were disposed of (in the skip!) before I could get hold of them when the firm closed its service department. (I was hospitalised at the time.) Tony I suggest that you check especially the accuracy and purity regarding noise and ripple, of the +5v, as this is fairly critical to the correct operation of the circuit. Tony. |
15th Feb 2019, 8:55 pm | #3 |
Pentode
Join Date: Aug 2003
Location: Halesowen, West Midlands, UK
Posts: 125
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Re: Technics PR305
I've just been searching the net only to find very little so I presume you're working blind fold (no circuit diagram). The next best thing to a diagram is the component data sheets these will give you the pin outs so you know what should be happening at various points in the circuit.
It sounds like you might have a missing voltage rail. From the bits of info I did find you should have two 15 volt main rails one positive and one negative going, you should be able to check this with you multi meter at the output connectors of the power supply PCB. If you're unsure post some good clear pictures of the inside guts, me or someone might be able to advise more. Good luck
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17th Feb 2019, 12:40 pm | #4 |
Rest in Peace
Join Date: Sep 2010
Location: Ripley, Derbyshire, UK.
Posts: 785
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Re: Technics PR305
I've just ferreted out my list of people I knew when I was in the trade.
I knew I'd still got it somewhere. This chap is of long experience, and should be able to help you if you get really stuck. http://www.mikebarden.com/ He is a genuine, highly experienced engineer, not a dabbler. I also tried searching for a service manual, and had no more success than Silvered Mica had. Dry joints / poor connections are still the most likely bet (in my personal opinion). Tony. |
22nd Feb 2019, 12:25 am | #5 |
Pentode
Join Date: Aug 2003
Location: Halesowen, West Midlands, UK
Posts: 125
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Re: Technics PR305
I agree with Tony it could be dry joints. power up and start taping the boards with the plastic or wood handle of a screwdriver and it might burst into life.
It could also be a transistor, FET or regulator gone bad. Is anything getting warm on the heatsink that is strapped to the power supply board?
__________________
Trust Me, It's a Magic Iron (∩ ͡° ͜ʖ ͡°)⊃━☆゚. * ・ 。゚, 📻📺🦔📡
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