Troubleshooting Tascam 38 channel issues

[WhinyLittleRunt]

Ok, 38 experts...

I dug out my Tascam 38 tonight after more than 4 years in the hopes that I might finally be able to get it working, or at least do a better job of assessing the issues. In truth, the unit hasn't worked 100% since I got it back in 2009. I've done a considerable amount of "n00b" work on it, like replacing all the VU bulbs, changing the drive belt, and reflowing the solder on the main connector board. It got so frustrating having a machine that barely worked, that I just dumped it to the side and when I found a 388, I bought that and never looked back... but from time to time would take out the 38 and set it up, thinking I knew what I was doing...

Well tonight I did know what I was doing, because I was finally able to fix a lingering erase problem that was the reason I left it for dead in the first place. It turned out that I had arbitrarily just messed with the adjustment of the master oscillator years ago, and by doing so I created a signal and erase problem that I could never seem to fix. So the other day I finally ordered a replacement oscillator board (Teac sells the actual oscillator still but the pulled part on the bay was cheaper and if it turned out to be a fried transistor or something, they're not common or available parts). Knowing I was getting a replacement I pulled the original one out and removed the adjustment screw entirely. Fortunately I had marked what direction it was set, but not knowing how many rotations to get back to the precise spot... so I put the adjustment screw back in all the way and began backing it out, lining up the notch with my old pencil mark, and recording some audio into a known-working channel. Each time I did this, the audio was choppy, clicky, going in and out, sometimes barely audible. But I repeated this process of backing out the screw and testing until I finally had a very clean recorded signal and was also finally able to erase that track!

With that 'fixed' (hopefully), I started testing out the individual channels and making sure they work in sync and playback in repro mode. I do have channel issues though. 1 and 4 did not get any audio signal on the VU meters nor did it record. One other channel, I think it was 6 but I can't remember now, got audio signal on the VU but didn't record (this one is questionable as I was rushing to record on all tracks in a specified order and possibly forgot to arm the channel). Anyway, here's what I found with the two known-bad channels:

-Channel card 1 did not work but after a series of reseating it, it finally started working. I don't trust this.
-Channel card 4 works in a different channel slot. Tested a known good card in slot 4 and got nothing. So I assume it's a backplane problem (the one I spent all that time reflowing..)
-The channels that do record work well, although they all sound slightly different. In fact, now that I think of it, I believe channel 1 was working when I recorded some test patterns and it was really distorted compared to the others... I know this could also be an alignment problem with an outside track. But some sound muddy, for example, compared to a good one that sounds very good and clear.

If I want to troubleshoot this any further, I suppose I will need to invest in an MRL test tape. For an intermittent card, or non-working card, what are some of the more common issues? Relays? Would it serve any benefit to recap the channel cards? Power supply?

I'm really trying to decide if it's worth keeping the 38 for the future, and if I go that route, I will probably go full-on restoration with it (to the limits of my ability). I know these are prone to similar failures and have caught a bad rap for being fairly unreliable, but they're probably getting fewer and fewer and not any cheaper, so I am inclined to hang on to it; my studio can't really facilitate its use due to space, but I'm not going to be in this house forever...

Any tips on how to troubleshoot and compare a working card on a scope or meter?

 

[Bob Joneson]

I just repaired a Tascam 38 last month. What an effing nightmare of a machine to work on, lol. I do electronics repair regularly, and restoration work on R2R machines, and I can say there is no amount of money in the world someone could pay me to work on another one.

After reflowing every single joint on the motherboard, and chasing literal ghosts in bad connectors, pots, etc..., I was able to finally get everything functioning. But only after nearly throwing it off the roof of my house at least 3 times. Tascam was the Behringer of the audio world at that time, competing on price and often at significant compromise in design.

I did this work on the cheap for a friend. At a standard tech rate, you could have bought a completely functional MX5050.

My advice... part it out for some other schmucks trying to repair theirs, and buy another deck with the proceeds.

 

[WhinyLittleRunt]

I just repaired a Tascam 38 last month. What an effing nightmare of a machine to work on, lol. I do electronics repair regularly, and restoration work on R2R machines, and I can say there is no amount of money in the world someone could pay me to work on another one.

After reflowing every single joint on the motherboard, and chasing literal ghosts in bad connectors, pots, etc..., I was able to finally get everything functioning. But only after nearly throwing it off the roof of my house at least 3 times. Tascam was the Behringer of the audio world at that time, competing on price and often at significant compromise in design.

I did this work on the cheap for a friend. At a standard tech rate, you could have bought a completely functional MX5050.

My advice... part it out for some other schmucks trying to repair theirs, and buy another deck with the proceeds.

I'll admit, it's good advice...

I actually don't need or want another deck; I'm using a Tascam 388 for my main recording and it functions (at the moment) flawlessly. The biggest kick in the bawls today was when I fired up the M308 mixer and found out that it itself wasn't functioning correctly on the tape input/monitor channels again! I'll tell ya I am getting closer and closer to chucking this stuff. Maybe just maybe someone would want the mixer on Craigslist if I let it go cheap enough, disclosing the problems... The 38 could be problematic because I can certainly part it out, but not knowing for sure if the parts are 'good' could really hurt me in a sale.

 

[Bob Joneson]

Do a search on ebay for "Tascam 38", and filter for sold / completed items. Even selling parts as is / untested / no returns, you could very likely put together several hundred dollars off the proceeds.

The channel cards, headstack, and motors would be pretty easy sales, even disclosing unknown condition.

They are still relatively popular decks, and the parts market is active.

Best of luck, whatever you decide to do with it!

 

[WhinyLittleRunt]

Hard call because I'd like to have it working...but, I'm having a problem still with channel 1 and now 8 for some reason. Took out the mainboard and had a good look at it and seems that I must have solder-bridged some connections on channel 4 and that's why it wasn't working. 1 is weird because when I push on the card hard enough it makes contact and starts working, and I reflowed the solder on all those connections... 8 I don't know what's up with that now all of a sudden.. Reflowed the solder on that channel too and now it's not working.

Seems like it's just way more maintenance than it's worth honestly... Between my 388 and 244 I can crank out some nice sounding stuff... Maybe you're right about parting it out, or seeing if someone wants the whole package (deck and mixer)...

 

[wkrbee]

Did you solder both sides of the motherboard? Some of those feedthroughs have to be soldered from the cage side.Intermittent VU metering and sync/repo output are symptoms of that.You have to pull the R/P cards to get at them. If you look at the schematic you will see that the output leaves the R/P card,splits into two legs,one going to the output jack, and the other returning to the R/P card for the meter amp circuit.The 38 is a piece of cake to repair once you know the few common problems they have-the flaky solder on the M/B is the main problem along with forcing the R/P cards in without making sure all the pins are aligned and getting them all bent to shit.Of course it can be a pain especially since the numbered connectors are labeled wrong on the big fold out schematic.Jim Williams had some nice mods for the channel cards, removing the transformer and changing the gain structure in the head amp to improve the bottom end.

 

[Bob Joneson]

In addition to reflowing the contact points on the main board, I also found broken traces from where the main board flexed inserting / removing channel cards on the deck I repaired. I agree, they can be fixed, but be ready to be frustrated.

The other thing I found was that the sockets where the heads plug in were intermittent even after significant cleaning. This was causing erase issues.

Just all kinds of stuff that's a sign of engineering to a price point.

 

[WhinyLittleRunt]

Did you solder both sides of the motherboard? Some of those feedthroughs have to be soldered from the cage side.Intermittent VU metering and sync/repo output are symptoms of that.You have to pull the R/P cards to get at them. If you look at the schematic you will see that the output leaves the R/P card,splits into two legs,one going to the output jack, and the other returning to the R/P card for the meter amp circuit.The 38 is a piece of cake to repair once you know the few common problems they have-the flaky solder on the M/B is the main problem along with forcing the R/P cards in without making sure all the pins are aligned and getting them all bent to shit.Of course it can be a pain especially since the numbered connectors are labeled wrong on the big fold out schematic.Jim Williams had some nice mods for the channel cards, removing the transformer and changing the gain structure in the head amp to improve the bottom end.

Well, yes to a point... I concentrated on the 2 channels that weren't working, and did do both sides... actually, I even made a point on some connections to just desolder and resolder them (I use a Hakko desoldering gun so it's super quick and easy). I'm thinking if the board has a crack in it riding somewhere near channel 1 causing the card to only make contact when it's pushed against, then it's probably not going to be hard to find since the break should be more relaxed without any pressure on it... I'll give it another go.. fortunately, the erase issue is gone, and what it will record it does record well. In the meantime, since it's related to my troubleshooting depression lol:

What do you guys think of the buss card issue in the M308? The one that's all crackly and distorted? There aren't any internal trim pots on it... I had posted a video of it previously in a thread a year or so ago:

(sorry about the heavy breathing...)

The card is pretty simple with just a few op-amps on it, no transistors or any other component that can cause a gain problem... It wouldn't really be that hard to replace them/shotgun it and see what happens. They don't come out easily as the faders and rear connectors are all wired directly to the card on both sides but I can free it up enough to swap parts... just curious if anyone knows what that is...