Sony TC-355 with a noisy left channel

[Nickersby]

Hi,

I've just bought this old reel to reel. There is lots of white noise on playback on the left channel. The noise is not present when recording and monitoring from source so I assume the amplifier section is ok. It is present when the source is "tape", and can be heard before the tape engages (as you start to turn the selector switch to "Play" but before the reels spin up) so I don't think it's the playback head either.

I read on here that the transistors on this model (2SC632 and 2SC634) can be a source of noise, so I managed to find a schematic and replaced the three transistors in the pre-amp section with KSC1815s. The noise is still there, but now there's an additional high pitched sound that repeats every second or so (this started with the replacement of the second transistor). So, I've actually made it worse.

Any help or advice would be appreciated. This is my first attempt at a repair like this, I understand the basics of electronics but am very much a novice.

Thanks,

Nick.

 

[Okke 70s]

Especially after replacing op-amp transistors you might have to do *a lot* of demagnatizing. Have you tried that?

 

[Nickersby]

Tried that, no difference, though I'm pretty sure the noise isn't coming from the heads. As I said, the noise is there when I start to turn the selector switch. I can move the tape completely away from the head and the noise is still there.

 

[Okke 70s]

To bad. Well, then it's time to start narrowing down. One place to start is where the wires form the head are connected to the PCB. Switch them left and right. If the noise is still on the same channel, you can be sure it's not the head. Then apply the same trick down the line. At some point the problem will switch to the other channel, and then you know the problem is just before that point. You can use the schematic to find out how the signal travels thru the circuit. If you need help with that, let me know.