Belt.
It's hard to judge in black and white what a TEAC authorized service depot would tell you in a sight-unseen estimate. I'd not take it as gospel.
The way I'd look at it is this:
-Repair tech time will always quote you high $, as that's their business, bread/butter.
-It's impossible to state the 688 "needs all rubber replaced", when sight unseen and by your description that doesn't seem to be the case. If the FF/RW work and the Play/Rec tape motion has failed, that's a single item: the capstan belt. NOT the motor or the OTHER rubber parts (as minor as they may be the internal tires of the FF/RW mechanism is a hefty teardown of the unit to replace).
-A SINGLE CAPSTAN BELT will only set you back $10-$15 at most, and can be replaced by yourself, DIY style, at a tremendous savings. It's an effort to do, but is far from brain surgery or rocket science.
-I'm fairly experienced in repair of these units, tho I've never cracked open a 688, but I can be fairly certain the capstan belt replacement is neither difficult nor costly. To scare you with repair costs is part of the modern propaganda to always push an upgrade over any repair effort. I said PROPAGANDA & that's how I see it.
-For $15 and maybe 1.5 hours downtime you could fix the 688 unit and move on.
-IF you junk the 688 without repairing it, PLEASE send it to me!!!!
-I KNOW you're just itching to buy a newer unit, as your very first post opened with this idea, and following posts continued on this line of reasoning. HEY, there's nothing wrong with an upgrade, but it's the concept that the failure of the 688 has driven you to this point or supports this idea which is a little overblown of an idea.
-I'd recommend calling TASCAM Parts Dept (323)727-4840 [I hope I quoted that phone number correctly again?]... and just ask to purchase the capstan belt for the 688. They should have it in stock for a reasonable amount, and you don't have to sweat the measurement.
-Otherwise, it might pay to open up the bottom of the 688, remove the belt and measure it. Then just size a belt that's appx. 1/2" shorter than your old & stretched out belt. That's what people do when they lack or need the actual measurement of the belt. Get in there hands-on and measure it, then you know what you're looking for in sizes.
-You've made a grand effort getting the 688 out, or so it seems. I'd carry on and take it to the end zone with the MINOR repair that belt replacement really is. Once you've done that you'll kick yourself at how easy and effective it is, and how much $ they want for this in bench repair time,... which is literally like high seas piracy. Bench techs know most people won't want to work on their own gear, and there's a lucrative market in being a bench tech. However, when you get to the nuts and bolts of some of this stuff, it's really not that hard.
-After that repair, you'll have your chumly and familiar 688 baby repaired and back in action, and you'll have access to all those archive tapes you created back in the day. I'm all for seeing the 688 fixed. I don't believe it needs an all encompassing "refurbishment", and definitely not a motor, but once you endeavor a repair by yourself, you kind of go in on an exploratory mode and take on issues as you come across them.
-HINT: A tech service might say "all rubber and the motor" either as a scare tactic, or DOUBLE-HINT: some tech services may not have a clear idea of what is wrong, so they go into "throw parts at the problem"-mode. I've seen it a thousand times, myself being a former systems & peripherals repair tech.
-ANY MORE reasoning, floating ideas or cheerleading the points about vintage analog Portastudios or DIY repair, and I'd think I was just wasting my time. I can see the reasoning behind giving the 688 repair a shot, as I've done a few Portastudio belts & rubber refurbishments, and it's not all that hard, but it pays of well for the effort.
-Good luck with your repair and upgrade efforts. REMEMBER, the two ideas are not mutually exclusive, and I think it's a disservice to pose them as such. You can have them both, but it pains me to hear that the 688 needs a belt and so is a lost cause requiring a total upgrade. I, and most others on this forum do not see it that way. That's with all deference to you, or people who don't consider themselves techies or capable of such repairs. You should consider trying it before writing it off.
-In the TIME I've taken to write posts on this subject, the DIY belt replacement could have been done already. Think about it.
Thanx for reading me!


/DA