Tascam 388 Story...

I would be a horrible hypocrite if I cared about such things...one reason I put these threads up is to invite general discussion about the subject unit or issues/discussion specific to another member's subject unit. That way when somebody in the future stumbles on the thread it might help with a problem, educate or at the very least entertain and I can't do any of that as well alone so I encourage folks to chime in and hijack away as long as it has to do somehow with the unit present in the OP. So...no sweat! :)
 
sweetbeats said:
I would be a horrible hypocrite if I cared about such things...one reason I put these threads up is to invite general discussion about the subject unit or issues/discussion specific to another member's subject unit. That way when somebody in the future stumbles on the thread it might help with a problem, educate or at the very least entertain and I can't do any of that as well alone so I encourage folks to chime in and hijack away as long as it has to do somehow with the unit present in the OP. So...no sweat! :)
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Cool, nice to know!:)
 
There is work to do regarding the fact that meter #'s 2 & 8 are not showing any level. It isn't a meter problem. More in the next post. I'll just show some pictures in this post before I start oozing the doom and gloom.

Just a few shots of the 388 in its present state getting ready to get it lined up:

IMG_6108_1_1.JPG


IMG_6109_2_1.JPG


IMG_6110_3_1.JPG



BTW, I've decided that I'm going to forego checking the tangency of the record/repro head...see the related thread here:

https://homerecording.com/bbs/showthread.php?t=295509

I'll check the azimuth but I expect it to be good enough. Looking at the mounting and adjust screws for that head they have glue on them and since the block looks good and was relapped and setup by JRF at some point I'm going to leave the tangency alone.
 
BUSS B PCB is messed up somehow...

Not sure when or how because it worked before, but at some point between the time I bought this thing and now 3 of 8 channels on the BUSS B PCB are screwed up. The BUSS B PCB is the card that the monitor mixer PAN knobs are on...the one that is lined up with the BUSS MASTER R fader.

The reason the meters don't show any deflection when signal is input to PGM groups 2 or 8 is because the signal isn't getting out of the BUSS B PCB. The BUSS B PCB is the card that actually has the opamps for all 8 PGM groups on it.

Here is a schematic.

I recapped it so it could be bad caps but it would be the first time in all the recapping I have done that I have had a problem with a Nichicon cap. Not to be discarded as a possible cause though...

So up the 388 went on its side and off came the bottom panel, and then out came the BUSS B PCB. I confirmed with test tone that signal gets from the PGM BUSS IN jacks to the BUSS B PCB, they just don't get back out on PGM groups 2 and 8.

To make matters worse PGM group 5 is messed up too. Tone gets in and out from group 5 but at about a fixed 2x gain. The BUSS L fader doesn't effect the level for PGM group 5 and a 316mVAC 1kHz tone comes out >700mVAC no matter what I do to the BUSS L fader.

I'm so tired of this...bad memories of getting the 58 into the studio booth and onto the table only to find I had killed it worse than I thought. There it sat all clean and shiny but worth nothing for what it was intended.

Maybe the 388 isn't that bad off but the PGM groups handle all the bussing to and from tape and the monitor mixer so as it stands (depending on what else is messed up) my 388 is a 5-track machine at the moment.

I'd just pull the BUSS B PCB out of the parts 388 but guess what? It has already been scavenged...7 of the 10 PAN pots are gone...I could transfer pots from the bad card to the parts card...arg...I hate this.

So what I've done so far is traced all the connections to and from each of the 8 pins of the TL072 opamps for PGM groups 2, 5 and 8 to their destinations (i.e. all the way to the card connection points) and they are all good; they match what I measure on the good group channel's components. CAVIAT: I didn't check capacitors yet because I'm not pulling components off the card yet which is what I'd have to do to check any of the caps...each opamp circuit has 6 caps...4 electrolytics and two ceramics. Could they be bad? Maybe, but I'm looking more to the 072 chips being bad.

I guess the next step is to power the card up on the bench and input tone to it and trace that and see if I can find where I lose the tone. I know the tone doesn't make it to the fader on 2 and 8...haven't even started to try and figure out what is happening with #5...so with #2 and #8 that would point to an issue with the first stage of the amp.

I'm open to any and all suggestions. This problem is less daunting to me than the last time I dealt with this type of issue, but nonetheless it is a real damper. I wonder what else is messed up and it would be nice just to have one working unit around here. Its my own fault.
 
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Okay...

I don't think its anything on the BUSS B PCB...I took my spare one (even though it is missing the PAN knobs for monitor channels 1~7) and installed and the symptoms exist just the same as with the original board, SO...

I'm studying the schematics further. I know when I turned it on recently there was some crackling when I engaged the PGM/CUE button to PGM mode...I couldn't see how there was any way signal input at a PGM BUSS IN jack could go anywhere but to the amp section on the BUSS B board, but I'm *starting* to see how the automatic switching might be able effect this if the logic chip was messed up...I need to study further but the switching...its like it could maybe allow input signal to couple...to ground if the logic chip was messed...maybe. Couple ways I think I could test this...hm...

Anyway, I'll likely swap the BUSS A and MONITOR PCB's out to see if things are working...look for charred stuff.
 
Go slow grasshopper

Don't pull any parts yet. Do like you said and trace a signal down a working chain and down a failed chain and see where it fails. Step by step and no leaps.

Then when you know where it is failing see if that is common to all failed channels.

Lastly, decide which part is the cause and replace it then trace it again if it all does not come to life.

--Ethan
 
Wish I had a useful idea to offer you Cory! :o

The only thing that comes to mind is if you have one channel which completely works from head to tail, use that as a reference on the bad ones to see where signals and readings get messed up.

If you've recapped certain cards, perhaps recheck to ensure you haven't installed any of them in reverse polarity.

Sorry, I'm not a technician.

Beyond that, take breaks, drink tea and don't take it too seriously by over thinking the issues.

Cheers! :)
 
Ghost...I like coffee...though that doesn't help with the over-thinking bit...like...um...right now.

I checked, rechecked and checked again the polarity of the caps, but it'll remain on the usual suspect list.

Ethan, thanks...hard to go slow. It is really interesting how the two BUSS PCB's and the MONITOR PCB interrelate...as far as the BUSS B PCB goes though there is a very simple circuit on there for the PGM BUSS IN jacks to the PGM BUSS OUT jacks...a basic dual stage gain amp with the buss fader in the middle...input jack prior to stage one, output jack after stage two...straight forward. The complexity comes in when it is realized that that two stage amp circuit drives the PGM BUSS OUT jacks and the tape section and/or monitor mixer. There is all sorts of transistorized switching stuff on the BUSS A and MONITOR PCB's to determine when/how the source (the PGM group) is switched for routing to the tape section or monitor mixer...signal is going to look for the easiest path to ground and I'm wondering if those switching transistors, if some are messed up, if signal could be shorted to ground from the BUSS B PCB to the BUSS A PCB leaving the available gain weak or non-existent to drive the PGM BUSS OUT jacks for he offending channels...I'll have to recheck but on #2 and #8 I think there is actually signal there, it is just really weak...might be possible...or...something. #5 is a whole 'nuther story...can't get to that yet...

I was going to pull the connector off the BUSS B PCB through which the output of each of the second stages for groups 1~8 pass to the BUSS A PCB...this would isolate the output of the second stage for each of the PGM groups to the BUSS OUT jacks...no chance for anything to go to the tape section/monitor mixer. It would be the definitive way to know if the BUSS B-PCB is good...

I was also going to switch the fader connectors to see if, perchance the problem follows the faders or stays put...

And I AM going to pull the BUSS A PCB and look/smell...

I just spent 2 hours grappling with my DAW interface driver setup debacle...thought I had the solution but I don't. Its amazing...I'd MUCH rather grapple with the 388 than the stupid driver issue...
 
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Could it be that simple?

The 388 PGM MASTER faders for the 8 groups are on 2 faders, one for groups 1, 3, 5 and 7, and the other for 2, 4, 6, and 8. I wanted to rule out whether or not the faders could be the problem. I was thinking no because I meticulously opened them up and cleaned them. I swapped the connectors for the faders to the BUSS B PCB. The dead groups 2 and 8 are now on 1 and 7, and the out of control group 5 is now on 6...so...its a fader problem...r...rrright?

To early...can't think quite straight. I'll test the faders out.
 
Here's hoping that it's indeed something straightforward, a relatively easy fix and not a revisit of the poor 58. :(

Other than that, the 388, cosmetically, looks pristine. :)
 
Guess what, everybody...

I picked away at the 388 here and there today amidst transporting kids here and there, working with the horses along with my girls, a myriad of weekend chores, family movie night, etc...

About three hours ago I finished putting the last trim piece back together on it. It looks fantastic. What a crisp transport too.

Before putting all the trim back on it I set the azimuth. It was about 45 degrees off which is still in spec, but it was quick and easy to pull that to around 0. It was wavering about +/- 10 degrees at 10kHz...I suppose that's normal?

Before that I recalibrated all the meters and checked the overload LED trigger point.

And before that? I finished repairing the BUSS MASTER faders. They were indeed the culprits...the EVEN fader had two channels (corresponding to groups 2 and 8 where the wipers weren't contacting the resistive element...I'm sure I took some spring out of them when I cleaned them even though I was super gentle. I reset the position of all the wipers in both faders. The ODD fader...weird (not a pun). Still not sure why group 5 wouldn't attenuate, but it was somehow the fader...and when I tested it the element that corresponds to group 3 wasn't conducting either...dead...maybe a hairline break in the element. I can see something got dropped on the control surface of this unit at some point in its life because I repaired a dent in the dress panel and the STEREO fader was trashed...maybe the BUSS fader took a hit too and now it just died. Anyway, pulled a fader from spares, cleaned it up and all groups work like a charm. :D

PHEW!

I've done some other tests and the mic pre for channel 1 is a little weak, and the ACCESS out for channel 6 is attenuated. Not going to worry about those things at this point if ever.

So next step is setting the tensions...go to grab my Tentelometer and...now where did I put that thing? Hmm...I recall loaning it out. ARG!

Oh well. Very good progress today and a huge relief.

I'll get some more pics up later with an update.

Thanks everybody!

:)
 
sweetbeats said:
I finished repairing the BUSS MASTER faders.
:)
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Hurray!!! (loud applauds here...)

I guess every story needs it moments of tension (though of course, I guess the tentelometer's up next :-)D)).

we were all rooting for you, though I've gotta say I'm glad you didn't have us on the line for too long...

i'll have some questions for you soon here...
 
(another) Tascam 388 Story...

So, I’ve been following here for a while, and not as an idle onlooker, but rather out of self interest – it seems I now have a Tascam 388 story of my own…. [What with the building progression in the last weeks of research, following the other stories here, mounting obsession, and final acquisition I feel a little like I’ve joined an exclusive cabal. (It’s certainly no good talking to people about this stuff at the neighborhood grocers… :eek: -glazed eyes-)]

My machine is in pretty good health, I got it from the original owner who, though not the overly meticulous or knowledgeable type, does not seem to have abused it and it was likely in commission for a mere five years or so. Following Sweetbeats story here is certainly an inspiration to give a bit more care in cleaning and setup before starting sessions than I would think to do otherwise, and now I have to decide how far to go. I’m not recapping anything I don’t have to, but I would like to perhaps do any cleaning & relubing where there might be some old grease, so as to avoid any stress on the machine and have ‘er smooth running as possible.

My interest at the moment is in the particulars of your (sweetbeats’) fader cleaning & relubing & pot cleaning process. The faders are pretty easy to get to (all the pots less so) as you can just unscrew them from the top and get at them from the back, unplug them from the channel, so…

1>what tool do you use to open up the fader casing? And bending the prongs back in place? My needlenose pliers seem a little rough on them.

2>what replacement grease do you use – you just put some up on the inside top of the fader case where the old stuff seems to have been? And what do you use to clean out the rest? The lubricant on mine doesn’t seem that bad actually, but I still might be interested in cleaning / relubing if I’m sure I’m using the right grease and won’t be ruining the ‘runway’ by cleaning it (don’t know what to call the two conductive/resistance lines on the inside of the fader – but they look sort of like a ‘runway’).

3> what do you use for cleaning out the pots (good old deoxit?) my pots seem like they could better use the cleaning than my faders actually – the trim knob on a couple channels seem to cut in midway distorting a bit when they do – this appears to heal if I work the pot a bit – and theres a few other scratchy pots - I’ll use some deoxit, but I don’t see how much of any gets to the actual pot from just spraying it on the top of the pot from the top of the mixer. Would be nice to do a more thorough job of it anyway, but I guess I’ve got to take out all the channel strips and get to the open side of the pots?

Though I guess this might be a bit rudimentary for some here, maybe a little in depth info about all this little stuff would also be of interest to others who like me havn’t yet cleaned their faders and pots from the inside.:)

And for the edification of those who’ve not seen these faders disassembled (like me until today…) I’ve included a mediocre photo:
tascam 388 fader.jpg

keep us up to date, we're all looking forward to the climax & grand finale!
and thanks especially for all the great photos.
 
Yes!

Another 388 falls into the hands of the rebel forces!!! :D

Don't be wary of running the machine and playing with it. I truly see it as a negative trait that I seemingly have to pull something all apart and clean it before using it. I truly think it is mild OCD so my way is definitely not necessarily the "right" way.

BUT, in answer to your questions:

1>what tool do you use to open up the fader casing? And bending the prongs back in place? My needlenose pliers seem a little rough on them.
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I do use needlenose pliers, but I wrap electrical tape around one of the jaws so it doesn't tear up the side of the fader body (when opening) or the rubber dust shield (when closing), and I tend to do more levering than squeezing.

2>what replacement grease do you use – you just put some up on the inside top of the fader case where the old stuff seems to have been? And what do you use to clean out the rest? The lubricant on mine doesn’t seem that bad actually, but I still might be interested in cleaning / relubing if I’m sure I’m using the right grease and won’t be ruining the ‘runway’ by cleaning it (don’t know what to call the two conductive/resistance lines on the inside of the fader – but they look sort of like a ‘runway’).
Click to expand...

I'm just using moly grease...good quality bearing grease...got it at Wal Mart in the automotive section...dark green stuff, and yes in the 388 fader I'm just putting it inside the top of the casing to replace the old stuff. I use window cleaner on a piece of t-shirt to clean out the old. The main reason I cleaned mine wasn't so much that the old lube as bad, but rather there were little dust-bunnies, hair, etc. in it and it was faster to just wipe out the old and put new in. DON'T LUBE THE "RUNWAY". That is called the resistive element BTW...the metal contacts are the wipers. I use DeoxIT Faderlube F5 to clean the elements AND the wipers. It is designed specifically for this application; for rotary and linear potentiometers. The DeoxIT D5 is for metal contacts and switches. I spray the F5 on the element track(s) and then gently wipe with a soft cloth, spray, wipe, spray until the cloth comes off pretty clean. Just be gentle. The Faderlube does a nice job of cleaning and it also leaves behind the right kind of lubricant that also assists with conductivity.

3> what do you use for cleaning out the pots (good old deoxit?) my pots seem like they could better use the cleaning than my faders actually – the trim knob on a couple channels seem to cut in midway distorting a bit when they do – this appears to heal if I work the pot a bit – and theres a few other scratchy pots - I’ll use some deoxit, but I don’t see how much of any gets to the actual pot from just spraying it on the top of the pot from the top of the mixer. Would be nice to do a more thorough job of it anyway, but I guess I’ve got to take out all the channel strips and get to the open side of the pots?
Click to expand...

Here's a thread that might help some: https://homerecording.com/bbs/showthread.php?t=272852. I've come to the conclusion that trying to force the cleaner through the pot shaft is a risky waste of time...its not going to flush the element off, and on te contrary its going to drag grease and dirt into the pot body. Hopefully the linked thread spells it out pretty well but you have to pull the card to get to the access holes. You may be able to stave off the issue for a time by rapidly sweeping the knob back and forth with a shoelace wrapped around the knob...I've used that technique a number of times with some good success. You want to use the DeoxIT Faderlube F5 with the pot as well.
 
Cory, everything lights up! Does it mean it's all fixed and running like a champ now? Wow, really great job but..... it was a cliff-hanger. ;)

I can't wait for you to finally enjoy the 388 and make some music!:)
 
You bet, Daniel...it was just the faders...had nothing to do with testing or experimenting...one of the posts up there a little ways goes over it...A good example of the care that needs to be taken when refurbishing. Some of the wipers in the BUSS MASTER faders had been bent just enough during cleaning to not contact the element anymore, so it was my doing, but it was easy to rectify. :)
 
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