TC-K707ES cam belt

[scan80269]

The cam belt in my TC-K707ES must be slipping, as the head block occasionally fails to fully engage in Rec/PB mode.

The TCM-200V16 transport mechanism does not make it easy to replace the cam belt, and much disassembling is required. I have a replacement belt, but just need to work up enough courage to do the disassembly.

[Scorpion8]

I have a replacement belt, but just need to work up enough courage to do the disassembly.

Use a digital camera, and take step-by-step pictures or use a note-pad and write down your disassembly steps so you can reverse them to re-assemble. I find the TCM-200(series) transports very easy to work on. They're my favorites, actually.

[A.N.T.]

The cam belt in my TC-K707ES must be slipping, as the head block occasionally fails to fully engage in Rec/PB mode.

The TCM-200V16 transport mechanism does not make it easy to replace the cam belt, and much disassembling is required. I have a replacement belt, but just need to work up enough courage to do the disassembly.

It could be also the mode switch is dirty and needs cleaning.

Cheers

Alex

[scan80269]

Thanks for the tips, Alex!

Whenever the problem occurs, the head block goes up about half way then stops, but if I give the head block an upward push within about two seconds after Play is pressed then it can fully engage all the way up. Coming back down is never an issue.

I guess the TCM-200 series mechs are easy to work on compared to Nakamichi classic mechs!

[Scorpion8]

Whenever the problem occurs, the head block goes up about half way then stops, but if I give the head block an upward push within about two seconds after Play is pressed then it can fully engage all the way up.

Have you examined the mode cam for crusty hardened grease in the pivot slot? Try to peek in there and watch.

[scan80269]

Have you examined the mode cam for crusty hardened grease in the pivot slot? Try to peek in there and watch.

Thanks for the pointer, Scorpion8!

I forgot to mention that the problem typically happens after the deck has warmed up for an hour or so playing a tape. Startups from cold are almost always normal.

[scan80269]

I finally replaced the cam belt in my TC-K707ES, and the heads have no problem fully engaging now. Getting to the cam belt was still tricky, but not as bad as I had thought.

This leaves me with another challenge with this deck: high wow & flutter. The TC-K707ES has a dual-capstan drive system unlike any other deck I've seen: the capstan motor couples via a short belt to the secondary (supply) capstan, not the primary capstan! Another belt interconnects the two capstan flywheels. This design can't be good for W&F. Sony specs are 0.05% (W.RMS NAB), +/- 0.14% (W.Peak DIN) and +/- 0.09% (W.Peak IEC), which are just about the worst I've seen for a dual-capstan uni-directional deck. Actual measurements with my W&F meter yield even worse numbers, so this deck is grossly out-of-spec.

Having replaced both capstan drive belts, the short belt between the motor pulley and the secondary flywheel wobbles noticably, so perhaps the replacement belt I got from Studio Sound Electronics (FBS5.8) is not the right one. The original belt is thinner, but has stretched and lost much elasticity, but ironically delivered slightly lower W&F figures. *?confused* The replacement belt between the flywheels is from Sony, but they no longer carry the short belt. Ditto for PartStore, Encompass & Andrews Electronics.

In any case, I suspect this unconventional belt drive design pretty much dooms this deck to have higher W&F than all my other dual-capstan decks no matter what, so I'm not sure how much more effort I should put in. Even extensive cleaning and lubrication of shaft bearings for both capstans has not helped.

[Scorpion8]

.... so perhaps the replacement belt I got from Studio Sound Electronics (FBS5.8) is not the right one. The original belt is thinner, but has stretched and lost much elasticity, but ironically delivered slightly lower W&F figures. *?confused* The replacement belt between the flywheels is from Sony, but they no longer carry the short belt. Ditto for PartStore, Encompass & Andrews Electronics.

The database I use doesn't show a FBS5.8 so did you have to stretch that one much? If it's making the capstan wobble, there's your source of W&F. This is what my reference database shows for that deck. You should contact MarrsCommunications (member here) and double check. He supplies the best belts around.

FBS8.0 Flat Belt, Small 8.0 Inch
Notes: Belt (Email us location details if you know) $5.95

FBS8.6 Flat Belt, Small 8.6 Inch
Notes: Belt (Email us location details if you know) $5.95

SBM2.5 Square Belt, Medium 2.5 Inch
Notes: Belt (Email us location details if you know) $5.95

[scan80269]

Thanks for the belt details, Scorp!

SBM2.5 is the cam belt. FBS8.6 is the belt between the two flywheels. The original short flat belt between the capstan motor pulley and the secondary flywheel measured at about 5.5 inches circumference, which led me to get a FBS5.8 from SSE as the closest match. There wasn't much stretching needed to mount this short belt, as the motor pulley sits quite close to the flywheel it drives. An FBS8.0 belt would be way too long so it looks like a database error for the TC-K707ES.

I also have a TC-K707ES belt kit from vintage-electronics.cc (Bob) which includes a flat belt with ~5.6" circumference. Both this belt and the FBS5.8 from SSE are noticably thicker than the original pulled from the deck, which, despite its weakened condition, showed little wobble against the motor pulley. The Sony belt between the flywheels has no wobble at all.

What I need is a thin (<0.025") belt with 5.5" circumference. I'm hoping Fred can help.