Tascam 388 Transport Trouble

  • Thread starter Thread starter kslight
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The early 388s had no regulation for the NST supply.The later ones had a series pass Darlington pair for regulation.It was never documented in any of the manuals.
 
That's the kind of valuable info that's going to get lost. So glad to have you contributing here, wkrbee.
 
Kslight, you'll want to refer your tech to wkrbee's post in case the 15V NST rail is being looked at. if your 388 is not an early model, the schematics won't match and wkrbee's input will be helpful. And I guarantee he knows precisely what he is talking by about.

Sorry I couldn't be of more help...best of luck.
 
Small update.

It's been at a tech for two weeks now, he sent me a message yesterday that he had just started to dig into it and said that neither reel motor runs from his external 24 volt supply.

I had purchased a "working" reel motor unit off of Reverb expecting a reel motor to be necessary, so I brought it in today. He hooked it up to his bench supply and sure enough...that one won't run off 24 volts either...

This is how he said he has tested motors on other 388s (he has another 388 two weeks ago when I dropped this one off).

He said the power supply on my 388 tested good.

He thinks he may be able to rebuild my motors and get them working, but will let me know.

Anyone have experience with that?
 
But both your YouTube vids of the problem show one or both reel motors turning, and we know at least the 15V NST power rail measured way out of spec (hosed) with your multi meter. I'm confused by the tech's claims the PSU is fine and all three reel motors are bad. Does his bench supply have enough current to drive the motors? I don't want to question the tech, but what he is telling you seems in conflict from what your vids show and what you measured.
 
I guess the brushes were stuck on the motor from Reverb. He says he got that motor going but my other motors are worn. He said he can rebuild them but waiting on parts.

I shared with him all the testing steps we have taken, and when I was there on Saturday I pointed out what I had measured as well.

I suppose I can just send him my videos for his information, in case they are helpful.

He seems like a knowledgeable guy, not some random kid at guitar center.
 
You're not recording with an alignment tape, so you don't need to worry about bias compatibility (i.e. it doesn't need to match LPR35).

You want the 1/4" 7.5 IPS 250nWb/m NAB tape 21T204.
 
sweetbeats said:
You're not recording with an alignment tape, so you don't need to worry about bias compatibility (i.e. it doesn't need to match LPR35).

You want the 1/4" 7.5 IPS 250nWb/m NAB tape 21T204.
Click to expand...

Thank you.
 
IMG_4814.webpFinally took it home today! And then brought my other machine in for alignment.


So many weird problems...I'm sorry if I'm skimp on technical details, I'm going to request a some documented specifics, but...

He rebrushed the motors. One of them still doesn't work, runs backwards and draws too much current, so I ordered a replacement motor and he rebrushed that one and installed it.

***does anyone have any experience with fixing a backwards running motor or is it trash?

A couple meters weren't working right in various modes. Bad voltage regulator.

A few boards weren't biasing right, it ended up being the trimmer pots were bad!

I think either an audio board or bias board was bad.


Some other stuff too, can't think of it all at the moment. But I had him align the machine and am getting ready to install in my new studio.

I didn't want to leave this thread open ended because that shit drives me crazy. This machine ended up being a bigger problem than any of my other 388s haha but I love them so consider this another machine saved from the landfill.
 
Only time I've had a motor run backwards was I'd inadvertently switched the wires. It's DC. It's polar. Switch the wires and it will run in reverse.
 
wkrbee said:
"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.
Click to expand...

Hi, I had this exact problem....and checked what you recommended, and this looked to be the issue.
No 15V NST present at P5 Pin4.

I have an original great Service Manual....but of course is useless because my Power Supply board is of a different Rev.
(I saw you mentioned this on page 5 of this thread.)

Question for you, since the old PSU had no regulation at all, can I just make my new PSU old.... and short around this Darlington Pair?
Feed 15V NST from P6-3 to P5-4?

What would be the danger of doing that? (It seemed to work when I tried it real quickly)
 
btw....pretty funny to read back through this thread.
The original guy trying to fix his 388 ignored all the good advice he got on here, then ended up getting wrong advice from a tech, and a machine with the motors running backwards? haha what?!
 
Follow up question for anyone....
My Brake (during record/playback) only seems to be dis-engaging like 80% of the time. For some reason others times it does not.
Any advice?

I tried adjusting the mechanism (screw A) as the manual suggests to get the 0.5mm spacing....but no luck yet.
 
Hey, so the first thing I would check is to see if the solenoid cushion has gone sticky.

The solenoids have a rubber "cushion", a stepped rubber washer that goes between the 'e' clip retainer that is on the solenoid plunger, and the body of the solenoid...it keeps the solenoid from going *klak* when it retracts. It is not necessary to the function of the solenoid...it is only to dampen the mechanical noise. But these rubber cushions can go gooey/sticky just like belts and idlers. If it has started to get tacky it will prevent the plunger from extending after it has been actuated, and in your case would prevent the brakes from releasing. Teac may still stock these cushions, or you can use any similarly-sized rubber washer, -OR- just get rid of it and deal with the mechanical noise present when the cushion is absent. If it has gone sticky, you can clean up any residue using isopropyl or denatured alcohol. And if you DO remove it and put something else different in its place, or even a replacement OEM part, OR just remove it and leave it out, in any case, you'll need to readjust the brakes.

Check and report back.
 
Thanks for the feedback!.....I checked to see if the rubber cushions are sticky, but they are not. So doesn't seem to be that.

(On a side-note, I don't really follow your logic on this one. The Brakes are on by default, and when the solenoid kicks off, it goes down into the plunger turning the brakes off. So if they were sticky, if anything I would be having the opposite problem...ie my brakes wouldnt be coming ON)

But anyways maybe I didn't describe my issue right, or not fully understanding. But they are not sticky.

Anything to check next?
 
I have the reels off right now....(and testing by just pushing the tension rollers up), and the brakes seem to turn Off everytime in this case (not 80% of the time)

So maybe this means it is related to the reels being on there? Which means something about tension being way off?
How am I supposed to set up the tension for this thing without a $500 tentelometer off ebay?
 
Ok well I think things are looking good here......the brake issue seemed to be purely a mechanical one.
I adjusted the solenoid a bit and it disengages every time now :)

Feeling good as usually solid in the electronics side of things....but suck when it comes to everything mechanical.

Would have never gotten to this point if I hadn't have found this thread and fixed the +15 issue first!
Still curious to hear feedback on that fix. (turning the regulated supply into an unregulated one)
 
When you said "no luck yet," my first thought was to refine that statement a bit. Is it (a) that you were not able to get the spacing specified in the manual; or (b) you got the right spacing but that didn't help. If you got the right spacing, you'll have to dig further. Since you said that the brake releases 80% of the time, I think that the person who wrote about the cushion becoming sticky is right on. If it were my equipment, I'd take the simple approach and just remove the cushion since it is not necessary for operation of the unit. In many cases, this equipment is connected by cables to something else so that no open mike is present, so the extra clank won't do any harm. I maintain that in this case removal is simpler than trying to clean the old one or find another item that will fit. If the cushion has started to deteriorate, cleaning might work only for a relatively short time.
 
Hi folks, reviving this thread as I'm experiencing an identical issue. Just picked up a 388 for a good deal a couple weeks ago. So far I have:
  • swabbed just about every board with isopropyl alcohol
  • cleaned all connectors with deoxit
  • checked all fuses
  • installed new capstan belt
  • recapped the power supply (which solved some intermittent electrical issues)
  • fixed a few lifted pads on the cap servo PCB
  • adjusted brakes according to the instructions in the factory manual
  • adjusted pots on the reel servo PCB (saw another post suggesting to change these pots out, mine all test good)
  • Cleaned reel tension sensors
  • Implemented Digi001's solution of feeding 15v NST from P6-3 to P5-4, which solved some odd transport issues
Still, I'm having an issue where the brakes momentarily release when engaging a transport mode (same thing happens in FF, RW, and PLAY) before releasing after about a second. In PLAY, the pinch roller also engages for a second before disengaging. I can verify that all other functions are working as intended in FF/RW as if I use my thumb to manually disengage the brakes, everything works as it should.

I'm genuinely stumped by this one and would appreciate any leads you smart folks might have. Who knows, I could be missing something obvious. Attaching a video showing the issue in hopes that can help make a diagnosis. Thanks in advance!

 
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