Technics RS-B10 Tapedeck repair - diyAudio
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Old 9th July 2012, 06:16 PM   #1
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Default Technics RS-B10 Tapedeck repair

Hullo all,

I wonder if someone rather better versed in interpreting circuit boards could help me out here. My father has the tapedeck above and it doesn't work. There's not a suspicion of movement from the machine when switched on and the buttons are pressed. I've got a service manual from the excellent elektrotanya but am stymied by the complexity of the thing!

I've ascertained that the motor spins when hooked up to a battery, so it's not defunct; I've followed through the power supply section where it comes in at 240V, comes out of the transformer at around 15V and enters the circuit board at about 13V. However, when the wire from the PSU section are connected to the circuit board (where it hits rectifier diodes etc.) the measurement suddenly drops tenfold to around a volt. As the motor needs 12, surely something's up?

None of the components are obviously damaged so I'm at a loss. Does anyone have any idea where all those volts could be dropping, or is anyone willing to take me through the testing procedures so I can gain an understanding of the circuit?

Yours in hope,

Providing sparkling relief to the palate and keen gratification to the whole wilted system.
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Old 17th July 2012, 12:12 PM   #2
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I am not familiar with that model so don't know if it's a reel or cassette machine. Most reel machines have sensors that detect whether a tape is "loaded" onto the machine -and won't allow any motion (including turning on the capstan motor) the unless it is. Have you threaded a tape - and nothing still happens?

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Old 19th July 2012, 02:38 PM   #3
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Hi Kaidanovshy,

I used to work on this stuff back in the day. I'll try to help you. It is funny how the memory starts to fade as you get older, if you know what I mean.

How much experience do you have with repairing electronics? You need to be very careful with the mains voltage. 240 volts can kill you if you make a mistake.

Do you have access to a good quality DMM or a scope? If you do, measure all of the DC voltages on Q16 and Q17 and lets get started.

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Old 19th August 2014, 04:12 PM   #4
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It's been a while, and I'd forgotten about this I'm afraid! I'm leaving to continue my studies in Sweden next week, but as I discovered this dismantled deck in the garage I thought I ought to carry on!

My multimeter's out of action at the moment, but I have an oscilloscope. I'm not well versed in them, having not used one since school physics, but I've got some readings out of it. Both Q16 and Q17 have a wave on them that is about +1.5V and down to -2V. How does that sound?

The 'scope is a Gould OS255 with two channels if that helps, or if you have some tips.

Hi Stellavox - it's a cassette deck and I've tried it with a tape in. I also think I remember it working (or the spindles going round) without tapes in before, so it may not have this detector mechanism.
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Old 19th August 2014, 04:28 PM   #5
kevinkr is offline kevinkr  United States
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Bad rectifier diode, shorted electrolytic in the power supply would be at the top of the list of things I would check first.
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