Tascam 388 Ch. 8 playback muddy

  • Thread starter Thread starter BennyS
  • Start date Start date
Unfortunately nothing happens when I lift the take up tension arm roller. Believe me, I tried every permutation of gently manipulating or adjusting all parts of the tape path that can be moved and this is the only point that seemed to change anything. I suppose I could try straightening the supply tension arm downward but I just want to feel like I know what I'm doing first. I'll check your channel for the video you mention.

Just so I know we're talking about the same thing, what I removed was a 1/8" inside diameter washer--which appears to be metal--that sits between the tape tension guide and the arm, is that the same piece? In any case I guess it does stand to reason that it's there to prevent direct friction between the guide and the arm. I hadn't considered what a temporary fix that may have been.
 
Hmmmmmmm…

No metal washer goes there…the order of the parts that go on the spindle of the tension arm is the:

1. Teflon thrust washer
2. Rolling guide
3. Teflon thrust washer (identical to #1)
4. Screw cap

See here:


IMG_2666.webp


Notice the same part #25 is identified for the upper and lower washers. It is a washer with 6mm OD, 3mm ID, and is 0.5mm thick, and it is NOT metal. Check and verify you have one on top and one on the bottom. Check the takeup tension arm roller as well. Be careful because sometimes they stick to the screw cap and/or the bottom of the rolling guide and people aren’t aware and they drop off when they’re not paying attention…critical washer gone. I don’t think you can get these from Tascam anymore. But they are crucial to the proper operation of the machine. If you have a metal washer there then you DO need to get rid of it…it’s not likely 0.5mm thick, and may damage the rolling guide or spindle shoulder. If I was a betting man I’d say somebody did the thing where they took the roller off, the thrust washer stuck to the bottom and then later jettisoned when they weren’t paying attention, and they thought they could stick any washer in there. Check both sides and tell us how many of the total of four washers are present. I *might* still have one NOS washer here if needed and you can certainly call Tascam and ask. But I wouldn’t use anything but the factory part there.

Here are links to the videos about tension arm adjustment on my old 48…takes a precision square, patience and a gentle hand…but I don’t think this is your issue…I think you have a thrust washer problem:



 
I'm assuming the teflon washer should be light colored or clear, not dark and reflective like the one I'm dealing with? It's just so small it's kind of hard to inspect. I can try to get a pic tonight, but all of the washers for the rollers--tension arm, pinch, etc.--look to be of the same material. The measurements you provide are what I got for the washer I have.

I do have some precision measuring tools so I can check the roller for 90 degrees against the top panel like you suggest in your video, though I guess that presumes the panel is flat and mounted exactly perpendicular to the roller.

I know you suggest factory parts only, but it looks like there are some options online for replacement teflon washers of the correct size. Is there any reason not to use these? Will be contacting Tascam either way.
 
...I'm also curious if the felt washers on some of these guides need to be lubed. The manual makes no mention of this that I've seen.
 
BennyS said:
Hello,

I've been recording/mixing with my 388 and ch. 8 playback has become unbelievably muddy. Since I first noticed the problem a couple days ago the heads have been twice cleaned with 99% iso alcohol, demagged, I've tried FF and Rew a few times over with the tape lifters disengaged, and none of this has helped. A few months ago I was having a similar issue but it was intermittent at worst and a head cleaning seemed to take care of it.

I will say that since the last time I observed all channels playing back properly, I have replaced the pinch roller rubber, made a slight adjustment to the pinch roller pressure to get it within spec, and adjusted the reel table heights so that the tape no longer makes contact with the reel flange. This issue--as a persistent and not immediately fixable one--has only surfaced after those adjustments, though I do not know if they're related.

I'm using ATR Master Tape and have been for the whole project.

I'm posting a pic of the rec/playback head here in hopes that there may be a visible clue.

Thanks for your help.
Click to expand...
Why does the head look different on the bottom track? This seems to be where the problem is. Maybe it’s time to have the heads relapped?
 
The washers are black.

The felt is, I think, to keep out dust and dirt. The bearings in the guide are oil-impregnated bronze. If lubrication is needed, thoroughly clean the spindle and bore and apply a small amount of refined oil like turbine oil.
 
sweetbeats said:
The washers are black.

The felt is, I think, to keep out dust and dirt. The bearings in the guide are oil-impregnated bronze. If lubrication is needed, thoroughly clean the spindle and bore and apply a small amount of refined oil like turbine oil.
Click to expand...
Yea looking closer I do think I have the factory washers. However I'm missing the ones that go between the top of the tension rollers and the caps, on both sides. Waiting to hear back from Tascam about availability.
 
BennyS said:
Yea looking closer I do think I have the factory washers. However I'm missing the ones that go between the top of the tension rollers and the caps, on both sides. Waiting to hear back from Tascam about availability.
Click to expand...
Let us know when you find out. Did you email or call? I call 100% of the time.
 
Unfortunatley Tascam doesn't carry those washers any longer.

However, I found a supplier (linked below) who has ptfe washers which are 3mm ID x 7mm OD x 0.5mm thick, so just 1mm bigger on the OD than the factory part. They're in stock currently, not expensive at all, and no minimum to order.

McMasters-Carr also carries ptfe washers that are 3.2mm x 6mm x 0.45-0.55mm, sold in packs of 25 for $15, in stock as well: https://www.mcmaster.com/95630A552/

I'm going to try the McMasters option since it's a slightly closer fit, though way more than I need. Will report back

 
The critical dimension is the thickness. I don’t know if PTFE is the correct material. Since the McMaster part has a thickness range I wouldn’t use it. The first option states 0.5mm. I’d go that route. Put the two factory washers you have on the bottom. Put the aftermarket on top.
 
Since PTFE is just the generic name for teflon it seemed like the best option in terms of material. And I figured since these were the washers to go between the cap and the roller and not between the roller and the arm a possible 0.05mm difference probably wouldn't be as crucial as it would with the bottom washers. I still have the factory bottom washers on both tension rollers.

At this point I definitely want to get washers where they should be, see how everything is playing back, and if need be try the tension arm adjustment you detail in that video.
 
New washers installed between rollers and caps, problem not solved (didn't expect it to be) but I haven't been able to try adjusting the arm because now the unit doesn't want to FF or rewind. It had been rewinding slowly recently, no problems with FF, but this time it seemed to want to rewind but just couldn't get started. I had to manually run the take up reel backward to get the tape off the deck. Manual says I need a tentelometer to measure and adjust tape tension, and they are not cheap, if they can even be found. Any tips?
 
That’s not a tape tension issue I don’t think. It’s an issue with the transport servo circuitry IMO, either a power supply issue, or power delivery issue to the motors during fast-wind, OR the brakes aren’t properly disengaging during fast-wind. My skill-set is more limited in troubleshooting the transport issues that are becoming more and more common with 388s. I’d start by reseating the power supply and reel servo PCBs, and when you do that inspect the pins on the motherboard to verify nothing is bent or corroded, and also look at the sockets on the PCB assemblies for any damage or corrosion…you may also want to inspect for bad solder joints. Then I guess the next step would be to verify correct transport power supply voltages during operation…you can get to the solder joints for the power supply PCB by placing the 388 on its side and removing the bottom cover…you can access the solder side of the motherboards this way…the bias, reel servo and power supply PCBs plug into the smaller Mother 2 PCB. Realistically I’m not going to have time to walk you through all of this step-by-step and regardless, unless you know more about this than I do, it would be somewhat the “blind leading the blind” because, again, servo systems are not my comfort zone. There are two power rails produced by the power supply that relate to the transport, a +15V supply and a +35V supply, and after the power supply the +35V supply branches into a +24V supply as well via a 7824 regulator mounted to the heatsink on the backplane. And the +15V audio power rail is also used on the reel servo PCB. It might be a little different, my ability to help, if there was a theory of operation section in the service manual, but there’s not, and to complicate matters further there are a lot of errors in the 388 manual. So what is already a relatively complex set of schematics to try and follow is made worse by misleading and inconsistent information. But easy steps are to reseat and inspect the power supply and reel servo PCBs and their pins and solder joins on the boards and motherboard, and check that the brakes are fully disengaging in fast-wind.
 
I found another thread which details adjustment of the two tape tension nuts on the reel servo pcb and with a minor adjustment was able to get the supply tension roller sitting a bit higher which allowed the machine to rewind and fast forward again as normal. Still working on the track 8 issue though...
 
Oh I thought you’d done that already.


Those are trimmer pots not nuts.

You’re not adjusting tension with those trimmers per se. The servo system applies tension based on the position of the tension arms. The tension arm position trimmers on the reel servo board zero the position of the arms according to the instructions in the manual so that during the different transport modes the optical sensors that are part of the tension arms give proper feedback to the servo system regarding what the tape is doing. If the arms are statically in the wrong position they send the system the wrong information and the takeup and holdback tension won’t be right. I must have misunderstood you already set the static tension arm position. Once the tension arm positions are set, then actual tension can be adjusted via deferent trimmers and using a Tentelometer.

So remind me what is it you do to the supply tension arm manipulation-wise that gets all 8 tracks to function correctly; that gets the tape to sit right?
 
BennyS said:
Ok, I tried things all evening: adding a shim under the take up tension roller to raise it, messing with the reel table height again, closely inspecting every point of the tape path. Finally one thing I noticed is that when I pressed the supply tension roller down--since there's a little play there, I assume by design since both sides have that play--all tracks played back normally. It didn't help when I pressed down on the take-up tension roller, so I knew it wasn't that I was adding tension (many ways to check that of course). The real giveaway was that if I kept that supply tension roller pressed down I could stop and start the tape and track 8 would still back properly, whereas if I let go, press stop, then play again, the track was all low and muddy again.

So, I removed the one tiny shim washer from beneath the supply tension roller and so far, problem solved.
Click to expand...
@sweetbeats
Here’s the post to his solution (last sentence)
 
That's right, pushing down on the supply tension roller is still the only thing other than pushing the tape up next to the playback/record head that makes track 8 play back properly.
 
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