Tascam 388 adjustments

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illuminations

Member
Hi all,

I've owned a Tuscan 388 for a while. It is still fully functional, but I want to take the leap into adjusting and calibrating the machine. I'm going to start acquiring the necessary items, but had a few questions first. Quick note, I'm pretty new to this so I'll be learning as I go.

I've adjusted the tension arms a few times in the past - most recently the right arm when I was getting extremely slow playback. I noticed this most recent time the adjustment trim pot for the right tension arm would no longer turn clockwise, like it was turned as far is it would go. Is there a way to adjust this? Is it simply a matter of contact cleaner, or does it need to be replaced?

Secondly, I would like to adjust the VU meters. But I'm wondering how this will affect the tapes I've already recorded on the machine.

Lastly, is this a decent multimeter for the general tape maintenance purposes? I've found one used locally.

https://simpsonelectric.com/images/File/datasheets/2608.pdf

I know there's a bunch here.

Thanks in advance.
 
So a little follow up. I should have researched the multimeter ahead of time. I ended up buying a Leader LMV 181A. It still needs to be shipped. I do have one question about the machine though. Do you know what kind of probes are compatible with this machine? It does not come with any. I have a very cheap digital multimeter with red and black probes - would these work?
 
Cheap digital multimeter with standard probes will work fine for measuring DC volts, but won’t work for accurate measurement of AC audio voltage across the audio spectrum. For measuring frequency response ya need a true rms measuring ac voltmeter that is reasonably accurate from 20Hz to 20kHz. I use a Fluke 85. It’s okay. Gets the job done anyway but there are much better meters out there.

To your earlier questions, calibrating the VU meters has no impact on the levels of signal going to tape or coming off of tape or monitored at the input. Calibrating the meters simply makes it so when the meter reads 0VU with a 400Hz tone input (I think I’m remembering right the reference tone on a 388 is 400Hz), the amplitude of the tone is -10dBV, or 316mV AC. It makes it so what the meters show you is calibrated to a known signal and level.

What trim pot are you adjusting for the takeup tension arm? Can you post a pic? Have you looked at the trimmer? Does it look corroded? You can try sweeping the trimmer back and forth to see if that improves things. If sweeping it doesn’t help, and you are adjusting the right trimmer, it’s not usually a problem with the trimmer, but either something else out of adjustment, or a component failure around the trimmer. It’s important you follow the steps in the manual exactly as the are, included preceding adjustments. You can end up chasing your tail because (for instance) maybe the tension seems off but you haven’t first checked and adjusted the brakes. Or if we are talking PLAY mode maybe the pinch roller needs replaced, or pinch roller pressure needs adjusted, or the capstan belt is slipping. I’d go that route first before assuming there is a problem with the reel servo board. Also, what kind of tape are you using?

Can you post a video of the problem you are having with the takeup tension?
 
Thanks for the reply, Sweetbeats. I'll have a lot to look into. I was hoping to use some holiday downtime to dig in and gain as strong an understanding of this machine as I can.

Regarding the Leader LMV 181A, I believe it fulfills the requirements you've mentioned. I'm mostly just curious about what probes I'll need to purchase to get the meter functional. Here is a link to the manual:

http://bama.edebris.com/manuals/leader/lmv181a/

With the tension arm, I'll have to check it out when I get home from work. I followed the procedure from this link:

Tascam 388 Maintenance, Repair and FAQ thread - Message Board

Essentially, I lined it up according to the description. It actually went just that far then maxed out, maybe a hair under what is described in the post. It was enough to get the Tascam to play and record.

I have a small collection of tapes, but mostly I've been using NOS Maxell 35-90, Quantegy 457, and occasionally Scotch 207.
 
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The Scotch 207 may be sticky-prone. Refer to the sticky-shed thread at the top of the forum. I can’t remember off the top of my head.

That voltmeter looks like it will work fine as far as accuracy.

I’m not sure I’m clear about what the quandary is with what probes to get. Can you link some examples of probes you are looking at so we can quantify your options? Probes are probes...you need probes. Get probes. :) Throw up some links and maybe I’ll better understand what quandry is.

And let’s back up on these test procedures...you DO have the Operation - Maintenance manual, yes? That should be your #1 reference source for servicing your 388, and in the order the tasks are laid out in the manual...there’s two main chunks that comprise servicing your tape machine: 1. Transport checks and adjustments, and 2. Recorder/reproducer electronic checks and adjustments. The 388 of course has a 3rd chunk that being the mixing section electronic checks and adjustments, but that’s of lesser interest or concern usually. So, you first get the transport dialed in, and then proceed to the tape machine electronics (the “alignment”), but it is very important you follow the order of the different steps and components of each chunk.
 
The Scotch 207 is fine, I think. I'm pretty meticulous about clearing the heads/tape path when I use the machine. There is rarely more than a speck or two when I use the machine.

Regarding the probes. I think I was thrown off because the probes I have for the digital voltmeter have sheath that goes over the banana plug, which is not compatible with the Leader voltmeter I bought. I guess I'll just have buy new ones without the sheath.

I am going to wait to use it though, and heed your advice to go through the transport adjustments first. A few of the adjustments call for a spring scale. Would either of these be suitable for the tasks?

American Weigh Scales - Digital Scales Wholesale

Feedback Sports Alpine Digital Scale | Competitive Cyclist

These were both referenced in other forums, but in regards to different tape machines.
 
illuminations said:
The Scotch 207 is fine, I think. I'm pretty meticulous about clearing the heads/tape path when I use the machine. There is rarely more than a speck or two when I use the machine.

Regarding the probes. I think I was thrown off because the probes I have for the digital voltmeter have sheath that goes over the banana plug, which is not compatible with the Leader voltmeter I bought. I guess I'll just have buy new ones without the sheath.

I am going to wait to use it though, and heed your advice to go through the transport adjustments first. A few of the adjustments call for a spring scale. Would either of these be suitable for the tasks?

American Weigh Scales - Digital Scales Wholesale

Feedback Sports Alpine Digital Scale | Competitive Cyclist

These were both referenced in other forums, but in regards to different tape machines.
Click to expand...

Okay on the Scotch 207. Keep in mind tape that is going sticky won’t necessarily shed, but may bind on the tape path causing over-tension. Just keep it in mind. I’m assuming you are having the same problem with the take-up tension arm regardless of what tape you are rolling though, yes?

And on the probes yes I see what you mean now...yes you’ll need some sort of probe with an exposed banana plug on one end to connect to the combo terminals on the Leader.

And regarding the spring scale, the one you linked might work, but I don’t know what the minimum measurable weight is and how fine the gradient is on the display. There are typically two things you use spring scales for on a tape machine: calibrating the brakes, and calibrating the pinch roller pressure. The two tasks call for different weight ranges...the brake adjustment procedure often measures in ounces, while the pinch roller pressure procedure is orders of magnitude more weight, usually pounds. So I have two spring scales with each with a different range. I use Ohaus scales. I think these are pretty common for our purposes here.

OHAUS | Spring Scales

So, again, that digital one might work just great, I’m just not familiar with it (but haven’t been in the market for a spring scale in about a decade), and you just want to look in the 388 manual to see what ranges you need to cover and the measuring accuracy and then cross reference that with the digital scale’s specs and see if it’s a match. If it works that’s great. Nice to have one tool to do the job than two.
 
Unless the brakes are slipping or grabbing,you don't need the spring scales.More critical would be the tape tensions.which you need a Tentelometer to adjust precisely.
Re.the tension arm position adjustment:as you said you can get close and that may be close enough. What has happened is component values have drifted or there is something wrong in the reel servo circuit.Also,unless you have a playback alignment tape any tape recorded on your machine will not be compatible with any other 388.
 
I finally had a chance to try the trim pot again tonight. I noticed something this time that I didn't notice the first time. The top of the trim pot has a a ring with a little tab on it. There is a little metal piece that prevents this tab from moving fully. In the picture below the trim pot on the left is for the right tension arm. It is turned as for clockwise as it will go because that metal tab is being obstructed. Does that mean that this can't be adjusted any further? Seems kind of strange. It's pretty much in place now, but I think it would be better if it was just a hair higher.
 

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I’m wondering if the trim pots normally only need to be turned a little normally? Mine has gone fully clockwise and still the tension arm is not high enough.

wkrbee do you think if the components values have drifted it would cause there to be an inconsistency in the tension? Maybe this is forcing the trim pot to overcompensate?

I have a spare machine. I’ll try to swap the reel servo card in the next few days to see if that helps things. Do you think it would be a matter of changing the caps? I’ve considered doing this throughout my second machine slowly over time until I’ve done them all anyway.
 
I still haven't had a chance to pull the spare reel servo card.

What I'm thinking about doing is replacing the caps on the spare card and then swapping them. If I do this with just the reel servo card, will there be any issues? Can it cause any problems with other part of the tape path or the tension? Maybe cause an imbalance of some sort? Like I mentioned in the last post, I'd like to slowly change all the caps in my spare machine and put them into my primary one. Is there any harm in doing this one card at a time?
 
I would definitely recap something one board at a time. That way, if you mess up and it pops a fuse, you know which card has caused the problem (i.e. the last one). You'll most likely have to adjust the tape tension a bit regardless.
 
Why don’t you start by just swapping in the spare reel servo card?

You won’t harm anything by swapping in a single card per se, recapped or not.

I suspect your problem is not related to a failed electrolytic cap though...could easily be wrong about that. But you should be able to achieve proper tension within the sweep of the trimmers. The thing is, you are not actually setting tensions with the trimmers that adjust the tension arm position. That’s only part of the procedure. You need a tentelometer to properly set the tension and then adjust the positions of the tension arms and who knows where your tensions are at until you do that. So there could be component failure, or you just need to do the full tension set procedure. Swapping in the spare reel servo board will tell you...something. And like I said there’s no compelling reason to recap it first. Just try it. That’s my advice. Where I’ve run into trouble on a 388 is trying to run it *without* one of the servo system boards or components installed...the 388 is kind of hairy to sort out problems like this because power rails go through several boards, but some here and some there and I’ve cooked something before because I took one board out and that resulted in an over-voltage elsewhere...I’m talking about the servo system boards, not the r/p, dbx, meter, bias and balance amp boards to the left of the cardbay...those can be in and out piece-meal with the unit powered, but the stuff on far right...cap servo, reel servo...keep those both in when powering the unit.

[EDIT]

You won’t *hurt* anything by recapping the reel servo board first...just want to reinforce that...jpmorris’ advice isn’t wrong or bad or anything. It’s just that electrolytic caps often handle switching time delays and that sort of thing in the non-audio circuits in addition to filtering, decoupling, etc...and I would look more to a bad connection, cold solder joint, failed or failing resistor or transistor for what you are experiencing.

Try the spare reel servo board.

[EDIT AGAIN]

Re-seat the connections to the cap servo board, and power supply...inspect the connectors and solder joints on the plugin boards, and look at the corresponding pins on the motherboard for damage, tweaks, etc.
 
I finally swapped the servo cards. The trimmers on my spare machine were actually maxed out (fully clockwise) when I pulled it. I plugged it in as is, and the tension arms were actually worse. The left was close to accurate but the right was barely lifting and wobbly. Seems like even if there is an issue with the card/cards, there is probably a greater tension issue going on. The problem is, I don't have a tenelometer and can't really afford one at the moment. They are just too much new. Is there any other way to check and properly adjust the tension without one?

A visual inspection of the solder joints and connectors doesn't seem to indicate any issues. I don't notice any discoloration or anything. I'll have to wait to check the pins on the motherboard though since I have to flip the machine over.

Thanks for the tip also about which cards are safe to pull while the machine is powered. My plan to recap was partially inspired by going through your long thread Tascam 388 story thread. I thought since I have two machines, I could slowly recap the cards on one and swap it out, just to keep the machine in good shape. I think that will have to take a back seat to at least figuring out how to get the tension sorted out.
 
If you’re planning on keeping the machine for a long time it makes sense to recap it over time. The very first thing to recap is the power supply. Unless you are just too curious about the reel servo board. But the fact things aren’t better with the spare board tell me it’s not a problem with the reel servo board per se. The first thing to do is to verify the power supply rails are producing the proper voltages and that the power is clean. And in this case it would possibly be beneficial to be able to load-test the servo and transport supplies. To do this you’ll need to fabricate some power supply extender cables. I have a thread on this somewhere on this forum...

Question, though...have you tried swapping out the power supply board? If it was me I’d probably put the original reel servo board back in and try swapping the power supply board with the spare one and see if that makes any difference. Also, mounted to the inside surface of that finned heat-sink in the back are a bunch of power transistors on a narrow PCB. Look for discoloration or bad solder joints there too.

Can you set tensions without using a tentelometer? No. This is one of those things likena calibration tape. For some reason people think they’re going to be the first to figure out we don’t really need these things to correctly setup or properly maintain our tape machines, but it’s a farce every time. I’m not saying this is you. I’m just saying you can’t set tensions without a tension meter...I got mine used. $100. You want to make sure you get the right one though. There are several models.

Visually check the transistors on the heatsink. Try swapping the power supply board. Do check the pins on the motherboard, including their solder joints on the underside of the motherboard. And consider this...without a bright flashlight and a magnifying glass one often cannot see cold solder joints, and sometimes even then they go undetected.
 
A few updates. I was able to swap the power supply PCB and there was no difference with the tension trim pot issue. So I think I will be recapping that PCB and then maybe the real servo PCB next just to be safe. Just have to compile the list of caps and find them online. I looked at the transistors under the heat sink and they look to be ok - at least no discoloration (I actually remember seeing an example of the discoloration when I went through the Tascam 388 story).

One issue I am having now is channel 8 is causing some static on playback. I was able to reseat the cards and it went away but it was come back again. I have not placed the crossbar that holds the cards in place back, so maybe just some residual movement has caused them to wobble a bit. Or maybe there is a connection that is bad.

I've been trying to find a tentelometer, but I guess I'll have to wait until the appropriate one comes up on the used market to do a full adjustment. I have the 2 compatible types written down, so I'm keeping watch. Anyone in the Chicago area have one then went to rent out?

In the meantime, I have purchased an MRL tape and want to get the playback levels straightened out. I have a quick questions about my AC meter though, and this is going to show my inexperience, but I'm gonna ask anyway. My meter has two inputs. According to the manual: the first #1 is a metallic ground (ground terminal when measuring voltage), and the second #2 is a plug, UHF type (connector for applying voltage to be measured). It also says, "Type M and type UHF connectors and twin-type banana plugs can be used because #1 and #2 are 19mm apart. Individual banana plugs may also be used with #1 and #2 separately."
A lot of ac meters I've seen just have 1 input, so I'm not sure which input to use. If anyone could shed some light it would be hugely appreciated.

We're in a winter storm here in Chicago and it's not stopping all weekend, so it's the perfect setup to stay in and fix up some electronic.

A big thanks for all the input and assistance so far.
 
What model AC meter do you have?

Have you demagnetized the tape path, and if so using what demag tool?

I wouldn’t be doing any electronics calibration (except for aligning the meters) until the transport is working right. If tensions are off that can effect high frequency response. That’s why the maintenance steps are organized as they are in the manual, transport first, then electronics. If you just pick and choose randomly you’re at risk of chasing your tail.
 
The AC meter I'm using is a leader lmv 181a. Here is a link to a photo: Avionics Specialist, Inc. (Test Equipment Manufacturing)

I demagnetize the tape path, though not all the time, using an Annis han d mag. I was able to track down the static on track 8. I tried the swapping bias cards first. Then remembered track 8 could be disabled for DBX so swapped a DBX card and the problem went away. Unfortunately, when swapping the bias card, I accidentally snapped the hooks that keep one of the white connectors on. Now it doesn't line up. Even though it's a spare I still want to fix this, so I'll have to track down a replacement. I've been so careful swapping these cards out. I think I pushed the connector against the metal guide rail near the pins. Ufff.

The meters are all I want to align at the moment. This should give me a chance to get acquainted with the AC meter and get finally have them aligned (I know they've been a little off since I got them). The thing about the transport is it is actually working fine. But given the issue with the trim pots, I think it will not be fine soon. I'll keep up a search for a tentelometer, or maybe just take it to a tech, if I can find one around, to get the tension issues sorted then do the other alignments on my own.
 
I just pulled the trigger on a tentelometer. It should be arriving today or tomorrow. So, hopefully, the initial issue with the trim pots is closer to be being solved.

Re the tentelometer - it comes with a 1oz and 3oz weight for calibration. I was able to find a sort of general tentelometer manual online, so I'm going to try to calibrate it. Cory, I watched a couple of your vids from a previous thread about calibration. It the end, did you find that calibrating pulling the weight in the forward as well as the rewind mode had much of an effect? Also, it looks like you were using only a 1oz weight - would the 3oz just be for additional fine tuning? The meter looks well-cared for (comes with a case, probes look shiny, generally clean looking). I still want to calibrate before using it with the tape machine.

I might try to make a video of calibration of the tentelometer, as well as use with the 388 to post to youtube. I may make similar videos for the other adjustments that will be made. It's kind of surprising they don't already exist.
 
OK, got things all set up and gave the meter a run. Play at points A and B were reading about a gram or two off, and FF was about the same, but got them basically squared away.

Two things to mention. First, there is a little wobble with the needle, but it only seems to happen after the tape moves for a few seconds. This is about a 2-3g variation, so I basically adjusted so the correct value was centered. Second, RR was high, about 120g where 80g is optimal, so adjusted the pot (which is wrong in the manual - had to jog my memory through a search for that one). The RR was overshooting when going back to zero in RR, going to about -24. It’s still doing this. This is after rewinding from about halfway through a standard reel.

So things seem to be mostly checking out. But my right tension arm trim pot is still maxed out in the clockwise position. So I think there is still an issue at hand. Maybe checking values in the reel servo and power supply pcb might be the next step.
 
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