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Yamaha KX-250 Cassettedeck output tick noise problem (electronic not mechanical)

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codebeat
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There is no service manual of the Yamaha KX-250, anyone? I have fixed the mechanism of this unit, replaced the capstan motor (bad quality shreeking one with a better one), replaced the belts and works perfectly fine. Perfect audio, everything works great. However after testing it many times I reassembled the unit and did another test. Some tick noise is present in the audio.

The tick noise is present when executing a function, for example REW (most worse of all), FF or PLAY (only a few spikes randomly), also when using the remote. It is not a problem of the mechanism (motor) or a ground issue or something like that, disconnected it and problem still exists. Maybe it has something to do with static electricity because I have used the unit without HEAD cables attached to the mainboard (head input pins floating) however the pre-amplification circuit is working fine except of the noise. There are two IC's in this circuit, UPC1330HA head selector and a LA3161 pre-amplifier.

The LA3161 is a 2-channel preamplifier that has a circuit to reject ripple. Is it possible this IC is damaged (because of a (static) spike) and because of that the ripple rejection is no longer working? When I replace this IC the problem is solved?

Any ideas or do have some people any experience with this or recognize the sound behaviour discription? Anyone who can point me into the right direction? 

Many thanks for any reply. 

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bluemoon
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Hi,

you have a problem with electrostatic discharge. There is a wire connected somewhere between head(s) and gnd. This wire is brocken and often you can not notice it becasue the insulation is OK. When plastic tape slide over head electrostaticli charge it and when potential between head and gnd is enough high you can hear discharge amplified by preamps.

bst regards

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codebeat
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Hai Bluemoon,

Thank you for your comment. I will check that however I don't think that is the problem because without head cables attached to the main board the problem is also there. Didn't notice this problem before. I will try what you just suggested, let you know my findings.

Kind regards,
Erwin.

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bluemoon
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Hi,
there is no importance did you or did not attach the head cabel, there is so high voltage between head assembly and gnd to produce small discharge to induce enough electrostatic influence on all electronic circuits witch can override disconected head cabel. I experinced this problem all through last century 80`s in many cases when this decks was important piece of hifi system. If you can attach a picture from inside whre the head assembly is, maybe it can help

regards

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