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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 8th Aug 2022, 5:21 pm   #21
ButchJames
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

So far I have ...
  • Cleaned all the mechanisms, and freed any joints.
  • Switch cleaned all with Servisol Super 10 (and a cheaper equivalent)
  • Removed the motor-to-flywheel idler, rolled it on grit paper, cleaned, then applied Rubber Renue. I may re-do this again later - but the improvement is already noticeable. Much less 'rumble'.
  • Cleaned and vacuumed the entire deck, including the main audio board - the latter was very dusty.
  • Recapped - all circuit boards, inc PSU. No previous work has been done to this deck.
  • Will later - replace all transistors on the audio board, and may later re-fit new transistors and zener diode in the PSU.
  • Removed rotted sponge materials, will replace later.
  • Take up brake is weak - will look into that later. I have to manually apply a 'brake' when in RW mode.
  • Probably there are some other things I've forgotten to list? .....
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Old 8th Aug 2022, 5:26 pm   #22
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

The top of the tape should be 0.05mm below the top of the upper erase head segment, for the record and playback heads it should be 0.025mm above the top of the upper segments.

That spec. was used in many Sony reel to reel tape decks, a magnifying inspection mirror helps greatly when cleaning or adjusting the tape path.

Lawrence.
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Old 8th Aug 2022, 5:44 pm   #23
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

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The top of the tape should be 0.05mm below the top of the upper erase head segment, for the record and playback heads it should be 0.025mm above the top of the upper segments.

That spec. was used in many Sony reel to reel tape decks, a magnifying inspection mirror helps greatly when cleaning or adjusting the tape path.

Lawrence.
Thanks Lawrence, later I may employ macro photography to help. I have some 1/4" leader tape somewhere in the house?

Yes, it is the track heights that I need to get right, then I'll probably use my Revox A77 1/2 track to generate a 10khz azimuth tape. A full track is the ideal reference, but since this may be hard to source, or expensive, I'll opt for a DIY 1/2 track recording. Should be close enough.
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Old 8th Aug 2022, 6:40 pm   #24
Restoration73
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

I was gifted a TC-645 some time back, not being used because the pause lever/button
was broken off and needs replacement, and I tend to use my Revox and Teac most.
Examining my machine, I can see negligible erase head wear despite the age of the
machine. By comparison the brass head of an Akai 4000D and plastic of Sony TC-366 are severely worn, and wear of plastic heads (not the pole pieces) is inevitable.
Worst wear I have seen is on the plastic heads on later Philips machines.
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Old 8th Aug 2022, 10:08 pm   #25
ButchJames
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

Correction to what I suggested earlier regarding the tape lifter bar - I cannot replace this because, for one good reason, any increase in its diameter would interfere with the tape flow during record/play modes. Silly me spoke too soon!
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Old 8th Aug 2022, 10:31 pm   #26
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

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The erasure problem has now been identified on my TC-645. Basically, it was the supply side tape guide setting. I strongly suspect someone in the past has been messing about with this? I have taken a shot of the setting; the blue spot identifies where the screw slot 'matches' its previous position - this gives me +- 180 degrees of 'play'. I've turned the screw just 60 degrees clockwise, and the erasure issues completely disappears. For now, this will do.
The clue was in the erase head's abnormal wear pattern, visible in your photo in post #1 (reposted and highlighted to illustrate).

At first you made no mention of an erasure problem so I (we?) didnt pay much attention to the photo. (I was more concerned you might create an erase problem by relapping a Ferrite head). After you mentioned an erase problem, I went back to your original photo to see if it was clear enough to show any misalignment in the wear pattern, which it did. At the lower edge it even shows both the correct and the incorrect wear lines (highlighted).


Erase heads sit on the same centreline as record and play heads but are slightly wider, erasing into the guard bands.Your erase head would have missed erasing the top edge of the tape (track 1), but also the top edge of track 3.

This isnt a specifically Sony issue. The 1/4 track specifications were laid down in the 1950's.

As you have now discovered, the problem was solved by one simple adjustment of the tape guide.
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Old 9th Aug 2022, 11:57 am   #27
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

Just replaced the motor run capacitors - the bonus now is that the capstan motor runs only luke warm. The removed caps were dated '1974', other unrelated caps are dated '1973'!? Will replace later.

I lubricated the motors a few days ago.

Very pleased so far with machine's progress.

My only criticisms of the TC-645 so far are:

(1) FF/RW => leftmost erase head wearing?
(2) The slightly crude method to drive the capstan, ie the idler method.
(3) No obvious way to disengage the spools so that the tape can be moved back and forth freely? Similar to that found on the Revox and others.

I'm still new to this machine, so obviously I've much to learn about it.

@Timtape: Thank you for your feedback. Yes indeed, the clue was in the double worn paths. However, I would still have re-capped and transitorised the bias osc circuit and studied related working voltages in that particular path chain, so no time was wasted in my opinion.
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Old 10th Aug 2022, 12:56 am   #28
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

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Originally Posted by ButchJames View Post

@Timtape: Thank you for your feedback. Yes indeed, the clue was in the double worn paths.
You're welcome. When tracing a poor erasure issue, checking tape to erase head alignment is just standard procedure. It can be checked very quickly in situ, perhaps with the aid of an inspection mirror. No need to remove the head or open up the machine.
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Old 10th Aug 2022, 2:47 pm   #29
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

Reference the tape fouling/rubbing the left hand side of the erase head during fast winding, I had a quick look at a TC-377, a TC-399 and a Head Deck Assembly (heads not fitted) off a TC-399.

The default position (in FF, RWD and STOP positions) for the tape lifter pin is at the bottom of its available travel in its slot, so this is different from the example TC-645 in question. As stated earlier in the Thread this is held in the down position by spring tension, this can clearly be seen in the first photo showing the rear of the TC-399 Head Deck Assembly. The second photo shows the front view.

The only time the tape lifter pin is moved is when FWD (Play) is selected this moves the tape lifter pin up to the top of its slot and allows the tape to contact all the heads. The third photo shows the FWD position on the back of 399 Head Deck Assembly.

With FF or RWD selected the tape does get pretty close to the left hand edge of the erase head, in the static condition it can get very close depending upon the actual tension on the tape across the heads.

Photo 4 shows Rewind (RWD) with a gap similar to Tim's of max 1mm, the gap actually was varying due to the Motor Auto Stop lever pulsing up/down.

To me it is the Motor Auto Stop lever (left hand side on the 377/399) that is preventing (probably not intentionally) the tape getting closer/touching the left hand side of the erase head. The lever is linked to the long dog legged lever on the rear of the Head Deck Assembly where its pivoted weight attempts to push the Auto Stop Lever upwards with the tape tension contacting the Auto Stop Lever stopping the Auto Stop Lever going too high.

If I push the Auto Stop Lever upwards (so it no longer contacts the tape) then the tape moves up and makes light contact with the left hand side of the erase head.

David
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Old 10th Aug 2022, 2:56 pm   #30
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

Thanks for the photos and description DM. I guess the using of just one tape lifter pin as opposed to two means it has to pull the tape back quite a distance to clear the three heads, seemingly only just making it.
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Old 10th Aug 2022, 3:13 pm   #31
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

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To me it is the Motor Auto Stop lever (left hand side on the 377/399) that is preventing (probably not intentionally) the tape getting closer/touching the left hand side of the erase head. The lever is linked to the long dog legged lever on the rear of the Head Deck Assembly where its pivoted weight attempts to push the Auto Stop Lever upwards with the tape tension contacting the Auto Stop Lever stopping the Auto Stop Lever going too high.

If I push the Auto Stop Lever upwards (so it no longer contacts the tape) then the tape moves up and makes light contact with the left hand side of the erase head.

David
My description above is a little inaccurate. The lever that I am calling the Auto Stop Lever is the dog eared lever on the Head Deck Assembly, this is the lever where its vertical section makes contact with the tape, the lever is also mechanically coupled to the short lever that actuates the Motor stop microswitch.

David
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Old 10th Aug 2022, 4:48 pm   #32
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

Thanks for the info David - interesting to compare the machines.

Yep, it appears that Sony's TC-645 alternative design with a different auto-stop mech (under the take up spool) has left the erase head exposed to tape friction during FF/RW.

Yesterday, I lined up a steel rule between the erase head and the tape lifter, and that very line ran ahead of the take-up tape guide - so erase head tape rubbing is unfortunately inevitable.

ITMT, here is an underside shot of the 645's head assembly mechanisms - by default the Tape Lifter is active (ie for the RW/FF state). I've labelled the relevant plates. It's quite easy to work out the mechanical logic of the system.

Eric.
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Old 10th Aug 2022, 9:54 pm   #33
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

Hopefully this picture is clearer?

Eric.
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Old 11th Aug 2022, 9:29 am   #34
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

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Quote:
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David
My description above is a little inaccurate. The lever that I am calling the Auto Stop Lever is the dog eared lever on the Head Deck Assembly, this is the lever where its vertical section makes contact with the tape, the lever is also mechanically coupled to the short lever that actuates the Motor stop microswitch.

David

Dog eared should have read dog legged.

David
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Old 12th Aug 2022, 3:21 pm   #35
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

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Originally Posted by ButchJames View Post

Yep, it appears that Sony's TC-645 alternative design with a different auto-stop mech (under the take up spool) has left the erase head exposed to tape friction during FF/RW.

Yesterday, I lined up a steel rule between the erase head and the tape lifter, and that very line ran ahead of the take-up tape guide - so erase head tape rubbing is unfortunately inevitable.

ITMT, here is an underside shot of the 645's head assembly mechanisms - by default the Tape Lifter is active (ie for the RW/FF state). I've labelled the relevant plates. It's quite easy to work out the mechanical logic of the system.

Eric.
Yes agreed the tape contact with the erase head does appear to be an unwanted feature.

The 645 not having the mechanical selector switch for the tape transport operations luckily does not have the horrible switched cam assembly that can sometimes be difficult to get operating correctly.

David
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Old 13th Aug 2022, 10:04 am   #36
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Default Re: Sony TC-645 1/4 Track R2R Erase Head & Issues

@David

That's one thing that put me off trying out a TC-399/377 - the selector switch! Thanks for the feedback and photographs.
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