Weak/No output on Tascam 48-OB

[lo.fi.love]

Hey folks!

A new problem has popped up - who would have thought?

I am getting very, very weak output from my 48. Some channels work (three? four of them?) but on others I get a very, very faint signal that I can hear only when I push the faders up on the channel, the buss, and on my stereo output.

I tested my setup and the problem comes down to the tape deck itself - it's not anything to do with intermediate connections, or with my mixer.

For example, I recorded onto track 1, and in repro monitoring, the needle moves as it should. However, I get a nearly-silent signal from the deck's outputs.

I haven't popped the cover off the deck to check, but might this be due to a bad fuse? Maybe? That's my first guess.

Any help will be appreciated. Scratch that - all help will be VERY appreciated!

Cheers,
Jeff

[lo.fi.love]

I just checked the fuses with my multimeter and they're all OK. Strange.

[staticmethods]

Hi lo.fi...

It might be that some contacts have gone intermittent on some channels. You could try pulling out and re-seating those cards for the bad channels. If the problem persists, try swapping the cards from a good and bad channel. Does the problem follow the card, or stay with that slot/channel?

That's where i started with my 38... I ended up pulling out all the cards and cleaning all the connectors. Hopefully it's something simple like that...

-Tom.

[lo.fi.love]

Originally Posted by staticmethods

Hi lo.fi...

It might be that some contacts have gone intermittent on some channels. You could try pulling out and re-seating those cards for the bad channels. If the problem persists, try swapping the cards from a good and bad channel. Does the problem follow the card, or stay with that slot/channel?

That's where i started with my 38... I ended up pulling out all the cards and cleaning all the connectors. Hopefully it's something simple like that...

-Tom.

That might be worth checking out. I'll look into this.

[lo.fi.love]

Quick update:

I pulled the cards, dropped DeoxIt in the receptacles and on the pins, and put the cards back in. Same-ish problem. Repro levels coming out of the deck don't match with what I'm getting on the console.

... And it's not a wiring issue, as best I can tell.

I disconnected and reconnected the dbx noise reduction (dbx 150x units). Calibrated them as best I could. It all seemed kind of off.

While I had the bottom of the 48 chassis open, I adjusted the Input VU pots on a couple of channels because they were incorrect. I poked around / trouble-shot some more, and realized that the deck probably just needs to be calibrated before I start digging any deeper. Too many things seem out of whack.

I'm borrowing a friend's 1/2" MRL tape tomorrow. I need to work the kinks out of my setup before I start suspecting other things to be the issue.

---

Edit: While I'm at it, I'm going to check the VUs on my mixer's meter bridge to make sure that they're reading accurately. I'll do this before calibrating the deck.

[lo.fi.love]

Just checked the buss outs on the mixer. 0 VU equals 326 mV on all eight meters. So, that's clear.

[sweetbeats]

My old 48 giving lo.fi grief...I'm gonna be sick...

Jeff, did you consider the relays? Any difference when switching between the sync and repro heads when playing back?

Does the problem follow the cards?

It sounds like a relay issue at first blush to me.

[lo.fi.love]

Originally Posted by sweetbeats

My old 48 giving lo.fi grief...I'm gonna be sick...

It's going to be OK, Cory! She's in capable hands!

Jeff, did you consider the relays? Any difference when switching between the sync and repro heads when playing back?

No, I didn't consider the relays. That's news to me, actually, and for some reason I didn't think to compare the sync and repro monitors. I will do this.

(When I say I have 'capable hands', I mean, 'I've retained and absorbed everyone's suggestions and information', and 'I complement it with what I learn on my own' )

Does the problem follow the cards?

I forgot to identify the problem cards, but I'm at the same number of problem channels.

I'm going to dig through that box of spare parts that you sent me. Do you remember if you included any channel cards?

It sounds like a relay issue at first blush to me.

I'll read more on what this means and then figure out a way determine whether this is the cause.

I was going to borrow my friend's MRL tape but I've been sick these past few days. I'm not feeling good enough to ride my bicycle to his house... I wonder if I can con him into driving over here?

[lo.fi.love]

By the way, the problem is on 4 of 8 channels. I don't know if this means anything, but I'm adding it anyway.

[lo.fi.love]

I just remembered that I did switch between repro and sync while recording 1khz tones across eight channels. The levels were different on either head.

[sweetbeats]

BTW, Jeff, when I said "I'm gonna be sick" I meant that a piece of gear I sold to somebody was giving them grief, not that I was worried about the machine.

No channel card spares in all the spares you bought......BUT, they are hearty PCB's...no reason they can't be repaired if needed.

So try swapping some cards...see if the problem follows.

"The levels were different on either head"...can you clarify what you mean here?

When I aligned that deck prior to sending it to you it lined up beautifully, so something has changed and I don't think its just drift...a bad relay will give inconsistent levels to no levels and it will come and go...levels could even vary during playback...sometimes you can get things to "wake up" by switching back and forth between sync and repro. That's been my experience anyway. I never touched the relays on that deck so they are as stock as can be and maybe they are getting on in age.

See if your symptoms match at all and try the card swap.

[lo.fi.love]

Originally Posted by sweetbeats

So try swapping some cards...see if the problem follows.

I will do this.

"The levels were different on either head"...can you clarify what you mean here?

When switching between repro and sync modes, the levels changed, as indicated by the VU meters.

When I aligned that deck prior to sending it to you it lined up beautifully, so something has changed and I don't think its just drift...a bad relay will give inconsistent levels to no levels and it will come and go...levels could even vary during playback...sometimes you can get things to "wake up" by switching back and forth between sync and repro. That's been my experience anyway. I never touched the relays on that deck so they are as stock as can be and maybe they are getting on in age.

Cory, if you don't mind, can you explain what this means? I am unfamiliar with relays, the purpose they serve, and how they might have a hand in this issue. ... Just so I don't go into this half-cocked.

See if your symptoms match at all and try the card swap.

I'll label the cards that seem to be having trouble and then swap them around. I'll do that this weekend.

[sweetbeats]

The relays are the gateways to where the signal comes from. That's the little clicking you hear when you switch it from sync to repro, etc. If the contacts are dirty or the relays are wearing out your signal is going to do any number of things...inconsistent levels to no levels at all, differences between sync and repro...the kind of stuff you are experiencing. The relays are readily available from places like Mouser or Digikey, etc.

[lo.fi.love]

I finally got my hands on a 1/2" MRL tape. I threw it on the deck and played it. A few observations:

1. The VU meters on the 48 indicated the right volume level most of the time.
2. The signals coming from tape outputs #s 1 and 8 are weak, as indicated by the buss VU meters on my mixer. They're lower than expected, and also suffer the following issue:
3. This one thing kept happening: On a couple of passages (250Hz and 500Hz, specifically), the VU needles for busses 1 and 8 on my mixer would slowly creep up to 0. I rewound the tape so I could shoot video of this, but when I pressed Play again, the needles immediately perked up and indicated the levels that one would expect.
4. Sync and repro levels, as represented by both the deck's VUs and my mixer's VUs, indicated different levels on the same channels between when I switched between the two heads.

For the most part, it seems like the deck needs a thorough calibration, but I'm particularly concerned about channels 1 and 8. The deck's output doesn't match the levels indicated on its VU meters. I'm wondering what this could mean.

If anyone is still paying attention to this thread, I'd appreciate some help or advice. If you've got any! This is such a strange issue. I'm almost tempted to take this to the local tech but I'd prefer to not spend that much money if I can avoid it.

I've yet to see if the problem follows the cards, but I will find this out this weekend.

I've been overwhelmed by the sheer amount of work I need to do on my equipment, but I'm trying to focus on one thing at a time right now.

[mastercontrolme]

I can't really add much, but I did have to replace the DIP relays on my 42, the RCA outs were exhibiting problems, so I replaced both channel relays and it fixed it. Did you try both balanced and unbalanced outs? I think these use different relays IIRC.

[lo.fi.love]

Originally Posted by mastercontrolme

I can't really add much, but I did have to replace the DIP relays on my 42, the RCA outs were exhibiting problems, so I replaced both channel relays and it fixed it. Did you try both balanced and unbalanced outs? I think these use different relays IIRC.

Huh... I'll try the balanced outs today. Thanks!

[lo.fi.love]

OK, big news!

I hooked up the 48-OB's +4 outputs to my 8-channel firewire interface... it's the only +4 device I own that is suited to this task. I put on the MRL tape and....


Everything is fine! No problems whatsoever.


So, I need to (presumably) replace the relays for the -10 outputs. Can anyone enlighten me on what this involves? I have the full manual for the 48, including schematics, so I'm going to start there.

Thanks for the help!! I'm so excited!

[lo.fi.love]

I've got the service manual in front of me. From what I see, there are four relays on each rec/play card, but I'm not sure which ones are specific to -10db output.

Anybody have an idea? I'm not quite sure how to test this, but I'll see what I can do.

[lo.fi.love]

OK, so I'm looking through the manual. And, I've pulled one of the cards for reference.

Relays K001 and K002 are the culprits. The manual lists two values for these components, "MR62-24S" and "G2V-2". I'm not sure which one of these is the part that I'm supposed to buy. Both appear to be dead stock, so finding the replacements will be difficult.

I'm wondering, though, if the fact that two values were listed for each part number means that either one could be used. They're both 24V DPDT relays, and appear to have the same pin configuration. Are they interchangeable? Anybody have any idea?

[mastercontrolme]

Good news. They are not that hard to replace actually if you are fairy good with a soldering iron. I got drop in replacements for the -10 relays at digikey, let me get the part number for you, I think I bought some spares. If not I'll remove a card from my 42 and let you know...

[mastercontrolme]

Ok here are some pics with the model number.

I also included a pic of the line out opamp replacement with new film cap that replaces the electrolytic.

If you go to Digikey and enter in the full model number of the part, it will take you right to it.

www.mastercontrolmedia.net/tascam/42relay.jpg

www.mastercontrolmedia.net/tascam/42opamp.jpg

As you can see I also socketed the relay and opamp for easy replacement if necessary.

[lo.fi.love]

Why is it necessary to replace the ICs, though? I thought the problem was limited to the relays.

[mastercontrolme]

Originally Posted by lo.fi.love

Why is it necessary to replace the ICs, though? I thought the problem was limited to the relays.

It is, I decided to replace the opamp and cap simply for sound quality reasons, you really only need to touch the relay. I am also assuming that the boards in the 42 and 48 are similar.

[lo.fi.love]

Originally Posted by mastercontrolme

It is, I decided to replace the opamp and cap simply for sound quality reasons, you really only need to touch the relay. I am also assuming that the boards in the 42 and 48 are similar.

The boards are identical, actually, according to the manual.

What difference did you notice after replacing the opamp and capacitor?

[mastercontrolme]

Originally Posted by lo.fi.love

The boards are identical, actually, according to the manual.

What difference did you notice after replacing the opamp and capacitor?

Well, the original opamp likely dates from the late 70's/ early 80's and electrolytic's are not so good for audio path. Can I hear a difference, hard to say, I think it does sound better, I noticed a fuller sound compared to stock, but I did not A/B it, so who can say for sure. I was in there anyway, so I figured I'd replace those components while the iron was hot.