Sony TC-366 won't stay in play mode

[Keith956]

So the saga of the TC-366 goes on. It's (almost) working enough to try some tapes on it. It does seem to play OK, albeit a bit wooly sounding, on a junk tape I have.

I then tried recording. With a CD player/amp connected to the aux in/line out, and the switches selecting 'source', the signal through that path was good.

In record mode with the switches set to 'tape' (i.e. introducing the tape rec/play heads into the signal path) the sound was faint and distorted.

On playback the recording was barely audible and the same distortion apparent.

Is this likely to be due to head misalignment? Or should I start trying to debug the signal to the record head and from the play head? Getting at the PCBs looks a nightmare. I have given the record switches a good clean with Deoxit just in case.

[ms660]

Did you clean the equalizer switch contacts?

The bias voltage is fed to the record heads via a section of that switch (S302)

Lawrence.

[Ted Kendall]

First thing is to try it with some decent tape, which is easier said than done these days.

[paulsherwin]

I doubt if the heads are seriously misaligned unless somebody has been twiddling. The factory alignment won't have drifted all that far.

[Keith956]

Originally Posted by ms660

Did you clean the equalizer switch contacts?

The bias voltage is fed to the record heads via a section of that switch (S302)

Lawrence.

Good point, no I haven't. I'll give that a try.

I'll get the scope onto it and see if I can check the signal path, probably not going to be until next week now though.

[Plus4db]

Originally Posted by paulsherwin

I doubt if the heads are seriously misaligned unless somebody has been twiddling. The factory alignment won't have drifted all that far.

They can actually Keith, after 40-50 years like any spring under compression, the head alignment screw springs can fatigue and move. This was the case with one of my heads on the Teac, the only one still with intact Loctite too.

When you think they're clean too, I would clean them again, with a judicial light polish rather than just IPA. Something like Autosol is good for this, but only polish until mirror-like further polishing will still produce a black swab and that it is pemalloy metal.

[Ted Kendall]

I wouldn't be throwing abrasive at any head unless I was attempting a re-lap.

[TIMTAPE]

It could be a combination of head wear and dirt caught in the resulting groove crevices. Especially the left track. Ideally the head face has no wear groove and where the tape abuts the head it should be mirror smooth, even when viewed with powerful magnification.

[Plus4db]

Originally Posted by Ted Kendall

I wouldn't be throwing abrasive at any head unless I was attempting a re-lap.

When you acquire an old deck it sometimes is the only way, since IPA will not be enough. One polish does a lot less harm than lapping which should be a last resort unless you are sure there is plenty of life in the head or you have realigned and prior grooves will never let the tape ride true. Micro polishing lightly once can restore a lot of performance.

[Ted Kendall]

On your own head be it(!). I've not found it necessary in decades of fixing tape machines. A length of matt surfaced studio tape, like BASF LR56, would do a better job of scouring the surface anyway, without the risk of mucking up the wear pattern.

[ms660]

I must have serviced hundreds of Sony reel to reel tape recorders back in the day, the only stuff I used for cleaning was meths on a cotton bud or cloth, if the heads were beyond it they got replaced, which was easier to do back then because of availability.

Lawrence.

[TIMTAPE]

You may know this already but in my experience, heads arent always inspected properly let alone cleaned well. My distance eyesight is OK but now with age, for stuff this close and fine, I always need a lupe, and viewing in a good, strong light, with the machine on its back to give a clear, direct view.

Unfortunately because of the large overhang of the hum shield can, the playback head's face in these is harder to see and to clean. But...

Very helpfully, the TC366/377 has all three heads mounted on a dedicated headplate. If you're prepared to tag and unsolder the small leads going to the heads, the entire plate can then be removed by unscrewing three screws, making inspection and cleaning much easier than in situ. The mechanical head adjustments should remain intact. And if the record and play heads have enough wear to justify a relap it's now easier to do that or send it to someone for the work.

Pictures are of the TC 377 Ferrite heads but I think the rest is the same as the TC366 headblock.

[Plus4db]

Originally Posted by Ted Kendall

On your own head be it(!). I've not found it necessary in decades of fixing tape machines. A length of matt surfaced studio tape, like BASF LR56, would do a better job of scouring the surface anyway, without the risk of mucking up the wear pattern.

How would it muck up the wear pattern? You'd have to scrub for a long time with a car polish with it's mild cutting component, that doesn't wipe away your much more delicate car paint, in one application. I totally agree with you that any abrasive compound no matter how mild is wrong and I am totally against the American fashion for it as regular lubricant and treatment.

I am talking about heads that have sat for many years and have surface tarnish that IPA doesn't remove and then very lightly, once only. If they are re-aligned and there is considerable wear to a pattern, then lapping, if there's still life in them, would be the only answer. Car polish won't get you there. I found it necessary and beneficial on the Teac I have, when I bought it, and cannot see any problem under a powerful scope - the recording and playback is pristine now, notwithstanding I had already calibrated it. It won't be used or necessary again, I hear you Ted