Tascam 388 Transport Trouble

kslight

New member
I know I know...you've heard this problem before...

First time poster, long time lurker...

I've worked on and fixed 3 other 388s in the past 10 years or so, but this one I just grabbed has me stumped. Trying to save it from being scrapped and pass it along to my singer...

I realize transport problems are common, but I believe I have taken a swing at the most common fixes, see below.

So seeking other troubleshooting tips.


Basically you hit play, it engages then immediately stops. FF and RW do the same, often going "limp" after engaging (insert joke) and becoming loose in the path, coming off the guides.

Friday night I had FF working, but I seem to have adjusted it to where it isn't right now. In fact, ff was working so well it was going quite fast (as I was adjusting the speed) that it snapped the tape on the reel as it stopped. I haven't gotten it working again after that. I also occasionally had play going, sometimes if I held the play button down. While playing the right tensioner arm would wobble up and down and the tape would unspool/spool incorrectly (would unspool a lose few inches before the machine would catch up).



I feel like I should be able to get there with the servo adjustments. I have been adjusting the trimmers on the reel servo PCB to the best of my knowledge (I've done this on other 388s so I know more or less what to expect).
It doesn't seem that any range of adjustment helps enough to get it to work reliably.

The behavior that is most odd is that when adjusting R112 and R212 (tension arms), they don't seem to visually move. I'm thinking this may be part of my problem.


What I do know...

1. Capstan belt is fine. Turns as it should, I put a new belt on just to be sure.
2. New manufacture/known good tape loaded.
3. I went to the hardware store and bought all new fuses. Behavior is unchanged.
4. I re-seated the reel servo PCB, no change.
5. When I first opened it, power supply connector "P803" was loose and at least partially disconnected. I reconnected this.
6. I swapped the reel servo PCB with my other machine, no change.
7. Tape path has been cleaned (some pieces were very sticky and I took extra care to clean it thoroughly).
8. I do have the original service book.


Appreciate any ideas. I have another 388 here that I could swap stuff from if I have to.

This video I link is not me, but it shows a similar problem, except their tape does not go limp on the tension rollers like mine does.

https://m.youtube.com/watch?feature=related&v=dfZmoNDUXAM
 
So I've popped top panel off, and loaded my reel.

I noticed that if I manually release the brakes (as opposed to hitting play) the tape will flow briefly freely until I let go. Perhaps my brakes are locked up or not adjusted correctly? I have never had to adjust the brakes on these, any pointers?

The left brake has more resistance than the right one. When I push its lever it barely releases.


Thanks

Edit: Following service book process I have got the brakes setup uniformly. No change though. :-/



With my non scientific iPhone level, I noticed each table is a little unlevel (to itself, from left to center to right), as well as tables are not perfectly level to each other. Not talking hugely off, less than half a degree it seems. How far off would they have to be to cause a problem?
 
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Also not sure if worth mentioning, I put it back together and if I press play/ff/RW and manually "assist" either reel, it'll stay running until I stop (or until I fall too far behind pace).

As I was doing this I noticed that tape threading through the left side binds slightly just before it enters the reel.
 
IMG_3651.JPG

As far as I can tell from the service procedure, this is adjusted correctly. However I've never messed with the brakes on a r2r before, so I could be mistaken. Here is the procedure and diagram.
IMG_3658.JPG

There is still a significant range I could move screw A up or down on the left or right brake which could widely open or restrict further the felts. Right now both sides are adjusted more or less to open identically. I didn't take a picture of this while I had it apart. I put it back together temporarily just to clean up and be sure I didn't lose the screws...
 
You are clear that anytime you are adjusting these types of brakes there are 4 adjustments to make, yes? counter clockwise and clockwise for both reel tables, and the tension is different for each table in the counter clockwise and clockwise directions. I assume you are using a reliable spring scale to make your adjustments?
 
To clarify, The only brake adjustment I made was per Step 1, section 1-3-2 (shown in the photo). I adjusted screw A on the left brake so that lever C is parallel to the solenoid. When I first pulled the panel off, I noticed that it was not parallel, and made a small adjustment, but left everything else as is.


I don't own a spring scale (recommendations?) to do the full adjustment, and I wasn't really sure that brakes are the issue as I've never experienced this exact problem before. Was hoping for someone to chime in with what I should troubleshoot next.

I'll have more time this weekend hopefully, to post a video to be more specific.

Thanks
 
"Basically you hit play, it engages then immediately stops. FF and RW do the same, often going "limp" after engaging (insert joke) and becoming loose in the path, coming off the guides".
You have lost the " 15 v nst supply". There is a 35v 300 ms pulse that energizes the capstan/brake solenoids.It ramps quickly down to a 15v "run" voltage.It could be as easy as a blown fuse-check them with a ohm meter not just visually- or a problem in the 15 v section of the power supply PCB.
 
Question:

You refer to connector P803. To save me the time of having to hunt all over the schematics can you tell me what to board that connector is mounted?

I watched the video. The reels are turning the wrong way when you hit play. I'm not certain if that's because there is a logic problem or something is wired incorrectly, or something else...not sure if the reels spinning the wrong way is because the logic is telling them to do that, or if they are turning the wrong way because they can't do otherwise and that's allowing the tension arms to drop in which case they *would* start to turn the wrong way. You probably realize this, but when you hit PLAY the supply reel should turn clockwise to provide holdback tension, and the takeup reel should turn counter-clockwise to provide takeup tension. They are both doing the opposite of what they should do when engaging PLAY which is allowing tape to slack on both sides...tension arms drop triggering the transport shutoff.

So what happens if you have a buddy manually support the tension arms to about the mid-travel position and you hit PLAY? Can you put up a video of that?

Other questions:

*Do you know any other history of the unit?
*Can you contact the seller and ask if it started suddenly or if there were symptoms that came on gradually?
*Any known trauma sustained by the unit?
*Were you aware of this issue prior to purchase?
 
The connector I referenced is on a small board mounted vertically behind the fuses. Cap servo PCB I think when I looked it up. It is plugged back in now. It was "loose" when I got it, but not disconnected, probably was making intermittent connection.

I see what you mean in the video. I'm not in front of it right now, will have to mess with it.



As for other questions...

1. No
2. I haven't contacted him further, but his report when I bought it was it had sat for awhile and then he tried to use it and didn't know how to fix it.
3. No detectable damage. Outside of the missing side panels, cosmetically near perfect...no missing screws, either, surprisingly. Curiously I did find a couple small metal pieces that look maybe like PCB standoffs rolling around inside, I set them aside but haven't thought about them much.
4. I bought it non functioning, I have had pretty good luck getting the transport going on these machines before without much beyond adjustments so I assumed I could fix it. And absolute worst case scenario, I didn't pay a ton for it if I have to scrap it, or take it to a tech (but I don't have any reel techs within a few hundred miles).

Thanks. I'll see that I can mess with it tomorrow night.
 
To update to the post on the previous page..


Tonight all fuses were individually removed/reinstalled and measured zero. They were brand new but thought I would check anyway.

These two metal bits were rolling around when I first took it apart a couple weeks ago. Not sure what they go to. IMG_3735.JPG
 
Okay to sweet beats... I held down the tensioners in the middle, only the left reel turned and unspooled its tape until I stopped. The right reel made zero movements.
 


Video per @sweetbeats

Also, I believe the brakes are releasing correctly, if I activate the tensioner (so the capstan is moving) with no reel loaded and press play, I can feel a substantial difference in the resistance on both the supply and takeup side.

Conducting the same test with FF can feel the release but the take up motor doesn't seem to try at all. Conversely, with RW the supply reel motor does try.
 
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To update to the post on the previous page..


Tonight all fuses were individually removed/reinstalled and measured zero. They were brand new but thought I would check anyway.

These two metal bits were rolling around when I first took it apart a couple weeks ago. Not sure what they go to. View attachment 99386

Flip the cardbay cover upside down, take a picture of it and post it. I think those are the spacers that should be press-fit into the cover for each of the 6 mounting screws.
 


Video per @sweetbeats

Also, I believe the brakes are releasing correctly, if I activate the tensioner (so the capstan is moving) with no reel loaded and press play, I can feel a substantial difference in the resistance on both the supply and takeup side.

Conducting the same test with FF can feel the release but the take up motor doesn't seem to try at all. Conversely, with RW the supply reel motor does try.


Yeah, thanks for doing that. I think you have a problem with the transport logic. The takeup reel should be spinning counter-clockwise and the supply reel clockwise. Takeup reel is doing a lot of nothing and the supply reel is spinning the wrong way.

Look again at the post wkrbee put up. He knows his stuff. I would heed his advice and do what should always be #1 and that's to make sure the power supply is producing what it's supposed to produce. If that logic supply he talked about is wonky or dead, it can make the transport do all sorts of weird stuff.

Check the power supply.
 
Yeah, thanks for doing that. I think you have a problem with the transport logic. The takeup reel should be spinning counter-clockwise and the supply reel clockwise. Takeup reel is doing a lot of nothing and the supply reel is spinning the wrong way.

Look again at the post wkrbee put up. He knows his stuff. I would heed his advice and do what should always be #1 and that's to make sure the power supply is producing what it's supposed to produce. If that logic supply he talked about is wonky or dead, it can make the transport do all sorts of weird stuff.

Check the power supply.

I'm not sure about the supply reel turning the wrong way. It seems to turn the same as other 388s I've owned, and the working one I have, and my 38. The take up reel is definitely doing nothing, I agree. But I can't see how the supply reel going clockwise would be correct.

As far as power supply and logic goes... I'm amateur on that stuff. How would you suggest diagnosing and troubleshooting this? And I have a working machine sitting here if swapping parts is practical and makes any sense.


Thanks for your help.
 
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okay, first of all, the reel table behavior I'm saying you should expect is with tape *unloaded*. Without reels on the machine, if you lift the tension arms all the way up and hit PLAY, the reel tables likely do nothing. As you slowly lower the tension arms the supply motor should begin spinning clockwise and the takeup motor counter clockwise. The tape must be under *some* tension on both the supply side and the takeup side. Ask yourself this: if the supply motor spins counter clockwise in PLAY, how can there be any tension on the tape? Understand that when the supply motor spins clockwise in PLAY with tape unloaded, it is doing so with very little torque. You can easily stop an empty reel mounted on the table in this state. The capstan shaft over-powers the clockwise spinning supply reel, but that's where the supply tension is maintained.

I don't know how to explain it better than that. If all your machines, with tape unloaded, have supply reels that spin counter-clockwise in PLAY, then I just don't know what to say because that's not how it works.

As far as testing the power supply you would need to tip the machine up, remove the bottom cover, locate the MOTHER 2 PCB and find the solder joints that correspond to the board connectors for where the POWER SUPPLY PCB plugs into the motherboard, identify from the schematics which pad is what, get out your multimeter and start measuring voltages. I understand that may not be within your wheelhouse, but you seem to have some experience working with these machines and don't seem to be afraid of opening them up and getting your hands dirty so I don't think it's something you couldn't do. Do you have a multimeter?

As a quick-and-dirty thing to try, swap the POWER SUPPLY PCB with your other machine. That's the board next to the REEL SERVO PCB. Keep in mind there is always the risk the problem isn't with a particular board you swap, but something downstream that cooked the board you are swapping...in short (no pun intended) instead of putting the spare board in and everything magically works, you might put the spare board in, cook it, and still not know what is the root cause. So just be aware. You could also pull the POWER SUPPLY PCB out of the bad machine, put it in a known working machine and see if the known working machine still works A-OK. That would tell you there's not a problem with the POWER SUPPLY PCB and avoid damaging a good supply. Of course, if the supply IS bad there's no telling if it might damage something in the known good machine. So there are risks either way, and then you might be chasing your tail, which is why the *best* thing is to get out your meter and see what the power supply is actually producing in the bad machine.
 
Thanks. I'm not trying to push your patience or anything. I have some experience with these but not a technician.

I'll see what I can figure out with measuring.
 
Thanks. I'm not trying to push your patience or anything. I have some experience with these but not a technician.

I'll see what I can figure out with measuring.

Damn. I didn't mean to come across like you were testing my patience or anything. You're not.

So do you have a multimeter?
 
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