[SOLVED] TASCAM 688 Tape Transport Issues - REW and FF

Cye3212

New member
Hi all!

I just recently came into possession of one of these great machines although it is not completely functional (but close). There seems to be an issue with the tape transport (go figure), specifically an issue with the rewind and forward fast functions where those functions only appear to work under certain conditions. I know there are few threads on here and other sites that details issues related to my specific one but have not had much luck - I hope the pictures/video I provide in this thread can help others with similar issues and save time + money.

First a little background...When I received the 688 I immediately popped the hood open to inspect the capstan belt and lo and behold it had melted away. I am currently awaiting a replacement belt in the mail and temporarily placed a rubber band in its place which seems to work well enough. All the other functions of the machine (with the exception of recording, haven't tested that yet) appeared to be good until I placed a 72-minute, high-bias type II tape in the machine and tested the transport system. The 688 seems to play the tape just fine (without any distortion of sound, even) although has trouble with REW/FF where it either rewinds/forward fasts incredibly slowly, or attempts to but then seizes up and does not, as if there is no cassette in the deck.

At first I suspected a slipping idler tire or, worst-case scenario, a faulty reel motor so I focused in on that area. I applied some silicone lubricant to the gears and some synthetic [sewing machine] oil to the motor post in the hopes that this would resolve the issue but no dice. I kept playing around with the FF/REW functions and noticed something odd: when I unscrewed the tape deck assembly and stood it straight up, perpendicular to the machine, the functions worked almost flawlessly but when I set it back down in it's normal position, the same issues came up. I removed the reel motor to have a closer look and it seems to work as it should; I have no way of testing if it is providing the proper amount of torque but seeing as how it functioned as it should when the tape assembly was made to "stand up", I would think that it is. I checked the idler tire too and it looks like it may need replacing at some point down the road but it looks fairly good for the time being.

Here's a short video I made describing the issue right after I removed the reel motor:

https(colon)//photos.app.goo.gl/RRH5YiVjeJhDyMGG9

And here's another video showcasing the problem with the tape transport (where I "stand up" the tape assembly and show how the FF/REW functions work in this position)

https(colon)//photos.app.goo.gl/SbSp3XwojaLJWmzK7

please forgive my wordage as I am still very much an amateur at all this DIY stuff :) I called the tape assembly as "transport" so scratch that. Also just to clarify, when I note that "gravity" has something to do with the issue my train of thought was considering issues with the gyroscope (?) within the reel motor or the tape spools or something else due to the downward force of gravity in that resting position which is relieved when the tape assembly is placed in a "standing" position - hope that makes sense, haha.

Any help would be really really appreciated.

Thank you!
 
Hey everyone!

So I finally got the transport to work!!!

Lo and behold the issue was all with the idler tire itself. For some reason I didn't really suspect it since the tire looks like it was in good condition but it was actually very slippery. Also I think the last person to own this machine had used silicone lubricant or something and got some on the takeup spools because it was pretty slippery as well. I used a degreaser (white vinegar) to try and remove some of the lubricant on the spools and I sanded down the idler tire quite a bit. After a bit of this, VOILA the transport was working like butter.

An interesting aside though, as soon as I put everything back the REW/FF functions worked perfectly but the Play function began to malfunction; the tape was playing just fine and then i noticed it slowing down more and more until it eventually came to a stop and the play button wouldn't even engage the heads anymore - heck the green LED wouldn't even light up anymore! As upset as I was after finally figuring out the transport issue I opened up the 688 again and tried to figure out what went wrong. I couldn't really pinpoint the issue to anything mechanical so I thought I'd have to dig up a schematic and follow the signal path all the way from button to solenoid to see what went wrong. Before I gave into all that, I figured it may have something to do with a capacitor or something so I focused on those - I noticed a cap that was touching the internal battery (that powers the display) and I bent that back into a semi-straight position away from the battery, I saw a couple others caps that looked kinda bent ou t of shape and straightened those up as well - VOILA the play function started working again! I can't really say for sure what happened but if anyone has any clues I'd love to hear!

Anyways all is good in the world and I wanted to share my success with ya'll in the hopes this may help someone. I actually still have an issue with the capstan motor where it plays continuously even when there is no tape in the deck and the motor gets REALLY HOT ina short amount of time so I need to figure that out in another thread...alas, the machine works and records so I am happy for now, hah Any tips on the capstan motor would be appreciated though...

Thanks for reading!
 
Well with the rubber band and all the other abstract working on the deck there are still parts in the mechanism that need cleaning with denatured alcohol and then application of new grease. I use Lubriplate 105.
I do not use white vinegar for contamination removal as it is slightly acidic. My cleaning is all done with Denatured Alcohol for many years now.
Idler tires can be replaced. The play function has nothing to do with capacitors that are sitting upright of not. When moving them, I don't think that
will make a difference. This kind of equipment and I have worked on all of the regular analog stuff a lot, is not that sensitive to detect if a cap is sitting upright or laying down. What probably happen is the cap was in the way of the panel to allow he buttons to contact the tact switches to activate a function. There are no solenoids in the unit for play as it is a newer design than that. More likely flywheel take off or Cam type system although there are some units that employ the gear C method. I have worked on so many that it is hard to remember each unit.

Belt selection is critical for a proper wow and flutter figure. A cheap or wrong belt and most belts on E bay are the wrong ones, can give you poor function of the deck. The Capstan bearing and upper motor bearing need to be oiled. A proper servicing of the deck will get you more use of it that the most least service which is what you have done. The flywheel need to be pulled out to get oil properly into the capstan bearing. I have been using AMS Signature synthetic oil for the last year and it has presented some outstanding specs most of the time.
Am I saying all this to get more work? No, I already have 200 units here now.

A hot motor usually means the wrong belt and of course lack of lubrication. When it burns out then you will have another fun project to research as the original motor will not be found. At least not a new one.
 
Hi Everyone!

Just wanted to add ANOTHER Update regarding my previous "fix" - it didn't last very long and the tire began slipping again so I just replaced it. My idler tire didn't look damaged at all but it did feel a bit slick (again). Now, I've scoured the internet and different local hardware stores looking for this particular-sized tire but it's been rather difficult - however I found a similarly working replacement that seems to get the job done. I found myself a similarly sized (same diameter) faucet washer although it is half the width of the original tire - I bought 2, gave them a LIGHT sanding, popped em in and the REW/FF functions work MUCH better than my previous method. With that I recommend to folks just please replace your idler tires. I walked into my local hardware store, brought the tire with me and matched it to a faucet washer the best I could.

[MENTION=130918]skywaveTDR[/MENTION]
Thank you so much! I really appreciate the tips. Thanks for clearing up my thoughts on why the play function was intermittent for some time. Just to clarify, I used a 4:1 dilution of the white vinegar in hopes it would be less acidic and I did not have access to denatured alcohol but I will try to acquire some to keep on hand for situations like this! I have since purchased a replacement belt from a 3rd party site (labelled as a 688 replacement belt) but I am a little unsure if it is the correct belt... looks a bit thin... The motor was running hot when the rubber band was on there and it is still running hot with this "capstan belt" so I guess it could still very well be lack of lubrication as well as a wrong belt. When I closed the machine back up again I used sewing machine oil to lube both the capstan motor post and the take up motor post. Just to clarify, the flywheel is the wheel connected to the capstan motor correct? The one that has the belt around it? If so I had removed it when I was replacing the idler tire and had made sure to oil (what I think is) the bearing. If not I will get back in there and make sure to do a better job - don't want any lack of effort on my part to take its toll on the machine. I would take this to get professionally serviced but it's a little out of my budget and I feel mechanical issues should be fixable for the most part given the right amount of know-how and research so fingers crossed I'll get this thing running 100%. Thanks again!
 
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I have found that the use of AMS Signature synthetic motor oil is making major improvements in all the oiling that I do. Some open reels have 7.5 IPS wow and flutter measurements of .024% which is not all that normal with regular oils.

Idler tires can be had from specialized places but I have found that the square seals as obtained from Mc Master Carr of the right size do the job more than sufficient and are verified as working in many different models now and due to the hardness and type rubber will outlast the original part.
You need to select a seal smaller than the ID of the nylon piece you are putting it on and then the outside is what it is. I clean these with Naphtha before using them to get rid of any lubrication from the mold they are made in. I must have at least 140 units out there now using these seals- they are not $7.00 each but more like $10/ 100. I have told people about this in the technical world. If they take advantage of it or not is up to them.

The capstan belt if the right size should go over the flywheel and make it to the center of the pulley shaft. The amount of stretching it over the pulley shaft is the amount of stretch that the belt will be under. In small mechanism like this the thinner the belt the better but those of the 12 to 20/1000" thickness are only found at Marrs as he is having them custom made in Japan. They can not come from any other place of that size.
That does not mean that you have to use that Marrs belt all the time. But there are some Sony, Nakamichi and Aiwa machines that MUST have them. Other more generic machines can work fine with a correctly selected belt from Consolidated Electronics and I use their belts a lot and have good results with them. Again- selection of the size and thickness is critical to get the right wow and flutter specs as well as the high grade oils we have today. I stopped using Gun and sewing machine oil when I found by accident this AMS oil and have used it ever since in all kinds of machines and the results are consistently good. How else can you get a w&F spec from a Teac A2000R down to .02%wrms? It is that oil.
 
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