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Sony TC-640 Reel to Reel wont stay in record mode

hippo008

hippo008

New Member
I was given a free Sony TC-640 reel to reel deck. It functions properly outside the lock on the record lever. The deck records onto tape very well, playback seems normal. The issue I am having is that when you put the deck into recording mode and press play + record at the same time the deck will lock into play mode but not record. If you hold down the record key the deck will continue to record until you release the record key.

I took out the button array and I noticed there is no locking slide on the record key like the rewind, play and fastforward keys have. What could be going on here?
 
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That was my very first step. The switch panel is listed as one complete part, it doesn't show the internals of the panel and what would lock the record button. There's no solenoid behind it either so that can't be part of the lock
 
don't know this one at all, but it may be something purely mechanical, a little swing latch type thing. I've had issues with those on other machines getting gummy and either moving slowly or not moving at all. Its one of those deals where you may have to get it apart enough to see how the mechanism works and what is and isn't moving. Its a set of pushbuttons, can't be all that much to it.
 
The mechanism moves smoothly, I don't think anything is stuck and gummed up. That's what makes this such a head scratcher for me. It feels like I'm missing something obvious
 
The buttons might move OK but if there is a small catch on the side that is meant to hold the record button down, it may be stuck. I've dealt with this in car tape decks. Buttons move when you push them, but the little bits that operate on light spring pressure maybe don't move so well. A lot of those small parts have very dinky springs and it doesn't take very much to foul them up.


either way if you can get eyes on the mechanism it will probably be fairly obvious whats supposed to be happening
 
I was looking at the mechanism yesterday evening. There's supposed to be a small sliding plate that locks the record key into position. The FF, RW and Play all have the small plates, however there are no plates on the Record key. I'll take photos later
 
Well you guys were right, I shouldnt have doubted the sage advice given here. It looks like the locking bar for the Record lever is gummed up. This begs the question though, how do I degunk this? I dont want to just shoot Deoxit in there and pray. Its an enclosed area, I cannot clean it with a Q-Tip and some Isopropyl alcohol. Can I put some new oil in there without risking damage?

This is a photo of the whole switch array with the Play switch actuated and locked. The Play, FF and Rewind key can all slide a locking tab to the left into the Record actuator well however the locking bar barely slides in.
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This is a photo with the Play switch locked and me pressing it down into its travel. You can see the locking bar barely emerging from the right.

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As a fun bonus, heres my recent Facebook Marketplace score. All the tapes but the Irish are brand new. The TEAC A-6300 is in fantastic shape. I am hoping to sell it and pickup a 7" deck for myself. Any suggestions? :D

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Looks like the record button isn't pushing down far enough to get the tab to slide over and lock it, or the tab is bent out slightly and not being pushed over by the play button. Could also be the tab on the record button is bent up slightly and blocking it.

I bought a big box of really cheap tapes for less than the cost of the empty reels. Of them, the only one that was sticky was one of those Sony PR-150's. I emptied it and use it as my take-up reel now, figure its a nice match for my Sony TC-777.

I believe the Shamrock is made by Ampex, and obviously the Ampex is made by them. Those might have gone sticky.

Will that Teac run 10" reels? If it will, that would be the one to keep just for versatility reasons.
 
I ended up fixing the TC-640. I used a sharp pick to gently slide the record keys locking tab to the right and added some oil to the mechanism. It works smoothly now, no problems. I put the Sony back together, it looks great and sounds great. Im sure it could use some new caps on the power supply and a new run capacitor. At some point maybe ill to a complete rebuild on this machine if my parents really love it.

As for the Teac, yes it does take 10" reels but doesnt have the 15ips speed setting. The Teac is nice in all aspects but its size, this bad boy is a behemoth. I have a small listening setup and I want to try and keep it small. If there are any 4 track 2 channel 10.5" decks out there I am certainly interested. Im partial to the Akai GX models and their very long lasting heads, maybe they made one.
 
hippo008 said:
As for the Teac, yes it does take 10" reels but doesnt have the 15ips speed setting. The Teac is nice in all aspects but its size, this bad boy is a behemoth. I have a small listening setup and I want to try and keep it small. If there are any 4 track 2 channel 10.5" decks out there I am certainly interested. Im partial to the Akai GX models and their very long lasting heads, maybe they made one.
Click to expand...

Actually, your Teac there is a bit more compact than the Akai units. The only 10.5" deck that comes to mind, that is significantly more compact is the Pioneer RT-901\909. The going prices are far from "compact" though......

The Revox A77\B77 are also a bit more compact-but not by any significant margin.
 
I actually just posted a thread about this, I am going to be selling my A-6300 and swapping to 7" decks. I am hoping to find something somewhat compact that can record in reverse and has long lasting heads.
 
Sometimes you can't win!

It looks like the Sony lost speed control on its takeup reel motor. Putting the deck into play causes the deck to spin at fast forward speed. Fast forward seems fast as well. Rewind the takeup reel spins in the correct direction just very sluggishly.

Could this be a run capacitor? I'm thinking it's either a run capacitor or one of the wire wound resistors somehow went bad.

No fuses blew so I don't suspect a short.

Any ideas?
 
the takeup reel doesn't really set the tape play speed, thats all done by the capstan and pinch roller. If the tape is pulling through at high speed, make sure the pinch roller is making good contact with the capstan.

With no load caused by the pinch roller, the two reels will run at basically full forward and reverse speed, depending which you're looking at. It will be relatively low torque though so you can stop it by hand. In FF or REW it will have considerable torque and you won't easily stop it by hand.
 
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