Tascam 246 problem!

[famous beagle]

This is a continuation of another thread called "Proud New Owner." That one started off as me just being excited about my new ultra-clean 246 before I'd had a chance to test it. After fixing the broken control and capstan belts, here we are now.

<sigh> Well, son of a bitch.

Good news: I replaced the capstan belt and the control belt, and now the transport is purring like a kitten.

Bad news: Upon testing, I've found that tracks 2 and 3 are recording at very low volume compared to 1 and 4. I've cleaned the heads (no residue showed on the swabs) and demagnetized, and I'm still having the same problem.

I first tried recording to each track through channel 1. Once the problems showed up, I tried recording tracks 2 and 3 through their respective channels, just for the hell of it, and it didn't make any difference.

Anyone had any experience with this and know if it's fixable?

Thanks

 

[The Ghost of FM]

It's fixable but it would involve calibrating the unit which you'd need the service manual to step you through the procedure. Do you have that?

Cheers!

 

[famous beagle]

It's fixable but it would involve calibrating the unit which you'd need the service manual to step you through the procedure. Do you have that?

Cheers!

I have the owner's manual, but I don't have the service manual. Is it available on line do you know?

Thanks

 

[famous beagle]

Ok I found the service manual.

Do you know if I'll need any special, costly equipment in order to perform the calibration?

Thanks

 

[The Ghost of FM]

Ok I found the service manual.

Do you know if I'll need any special, costly equipment in order to perform the calibration?

Thanks

Just to tweak the recording levels back up, I doubt it.

The service manual should document what gear you need for that and more importantly, point out which internal trim pots you need to adjust to get the levels back up. I suspect the pots are just oxidized from long term non-usage and exercising it, (turning it back and forth a few times), will fix them up.

Cheers!

 

[Beck]

Yep, there is quite a bit of equipment you'll need, and that should be listed in the service manual. I'm out of town and don't have access to my service manual at the moment, or I would tell you what page that is on.

Before you start getting in that deep, see if you can figure out whether its recording low or playing back low by flipping the tape over. It will playback backwards, but on different tracks. If tracks 2 & 3 really have the same problem, an alternate way to check playback level is with a prerecorded commercial release. Also record steady tones, preferably 1 kHz on each channel so you can get an idea of how many dB difference there is between the input signal and playback.

 

[Beck]

I suspect the pots are just oxidized from long term non-usage and exercising it, (turning it back and forth a few times), will fix them up.

^^^^^This

That could save you a lot of trouble. Mark where the trimmers are now, then turn them back and forth before bringing them back to the original position. The bad thing about many decks in such good condition is that they have often sat idle for a long time. The good news is a little tweaking can often bring things back in order without having to do a full calibration. A full calibration from scratch is a PITA!

 

[A Reel Person]

As with other recorders,...

to get the playback levels up to snuff to begin with you'll need a calibration reference tape. Obviously, that's something that very few people have, but there might be a workaround for that. If you have the 414mkII or 424mkIII, you can make yourself a rough reference tape from those,... as long as you don't expect it to be factory correct. Keep in mind that there maybe a phase reversal in every other head,... difference between the 424 and 246, however, this should not represent any real problem. Just to be aware of it. An authentic test tape would be more accurate. You can tweak it back into line fairly easy. The problem itself would be fairly common and not too serious. Some of that comes with the territory with this older gear. The manual is essential.

 

[The Ghost of FM]

Another quick pre-test would also be to try the dbx bypass switch on the back of the unit BEFORE you start diving into a tedious calibration process.

Doing this can help determine if the level issue lays with in the dbx circuitry itself, which is a different set of calibration levels or to see if that switch itself has become oxidized. So again, switching it back and forth several times might clean off any possible offending oxide build up.

If that switch test shows no change in the levels issue, then you can at least determine that the dbx circuitry is not the issue.

And this all about eliminating suspects which reduces the number of possible problems. Plus, any calibration procedure would be done with the dbx bypassed anyway.

Cheers!

 

[famous beagle]

Ok thanks much for the info y'all. I'm on a timetable, because I have about 8 more days in which I can return the unit for a full refund. So I'm not going to be able to procure any fancy ocsilloscopes or tone generators. I'm hoping there are some computer programs I can use instead.

Dave: I don't have either of those units (414 mkII or 424mkIII), so I'm guessing I won't be able to use a reference tape at this time.

Really, my main concern at this point is that I just want to make sure that it is indeed just a calibration problem. I can always worry about taking the time to get it up to spec later if it bothers me, but right now I just need to make sure that I don't get stuck with a lemon, so time is of the essence.

I'll start off with the suggestion of "exercising" the internal record level pots and the DBX switches (and trying to record without DBX engaged) and see what happens with that. Thanks!

 

[famous beagle]

Tools, tools, tools

Ok, so I took a look at what was listed in the service manual just out of curiosity, thinking I may eventually get some of it as needed if I wanted to get the machine close to spec. (I still haven't tried exercising the calibration pots yet -- just thinking ahead here.)

And I have some questions that maybe some of you can answer, as I don't have much experience with most of these tools listed:

Linear Tension Gauge: I googled this exactly and didn't get much. I get tons for "tension gauges," but I've never dealt with one, so I'd have no idea what I would need for work on the 246. The only spec it gives is 0 to 500 grams. I saw lots of tension gauges on ebay that fit that bill, but none of them said "linear." For example, here's an affordable one:

Halda Haldex AB 1000 Gram Tension Gauge | eBay

But I don't know what to look for.

Torque Meter: It says "cassette torque meter." Again, nothing came up when I searched for that on ebay. But I did find an older HR thread that mentions the fact that they're rare but do show on ebay from time to time. After seeing a picture of them, I see that they actually look like a cassette, so I'm guessing anything other than a cassette torque meter wouldn't be of any help, correct?

Thanks for any help on this

 

[famous beagle]

Just to tweak the recording levels back up, I doubt it.

The service manual should document what gear you need for that and more importantly, point out which internal trim pots you need to adjust to get the levels back up. I suspect the pots are just oxidized from long term non-usage and exercising it, (turning it back and forth a few times), will fix them up.

Cheers!

With regards to this, would some Deoxit help matters at all?

 

[The Ghost of FM]

With regards to this, would some Deoxit help matters at all?

De-oxit is for switches and jacks. Pots require a different product.

But before you go on a parts buying spree unnesasarily, just try exercising the pots first, as this will often do the trick all on its own. And also heed what Beck said about marking the position of where the pot was first so that you can avoid doing an entire calibration job which may not be needed.

Also keep in mind, my original suggestion about getting the service manual was to locate the record trim pots on the circuit boards...and not because I was suggesting a total calibration.

Also, buying a Tentelometer, (tape tension meter),new, would cost more then you paid for the 246. You also said earlier that the transport was "purring like a kitten". Don't mess with something if it ain't broke!

To recap:

Exercise the dbx bypass switch first and try your recording test with it again off and on. If that doesn't fix the issue, then open the unit and find the record trim pots. Those are two likely suspects at this point. Concentrate solely on those for now before you worry over the rest of it.

Cheers!

 

[famous beagle]

Oh, wow, really? I've used De-oxit on pots for years with great success. What are you supposed to use on pots?

Yeah, I wasn't ready to buy a bunch of parts just yet. I was just curious really. I don't even really know what the parts are used for.

And your recap suggestions are on the agenda tonight, so let's hope that does the trick.

If it doesn't, however, could I get close enough with just some trial and error? In other words, record some pure tones and watch the meters, then play back and watch the meters. Then make and adjustments and try again until it's close. I mean, are those internal record calibration pots just kind of like little volume knobs, or is there much more to it than that?

Thanks so much for all the help!

 

[The Ghost of FM]

The trim pots are similar to regular volume or tone pots only they're not encased with a metal shield cap around them and are designed to be turned by a small plastic screwdriver instead of your fingers. They do this to save space. Otherwise, a pot is a pot is a pot I suppose.

About the proper cleaning product for those, I believe its called DeoxIT® Fader F-Series

DeoxIT® Fader F-Series

If those first two check items don't pan out, I'm not sure what to suggest after that. Playing a pre-recorded tape would be good for check the repro level pots with and would also tell you if its an input or output level issue. Any tape you have with fairly constant levels, like pop music would do lacking a proper calibration tape. If that plays back without issue, then you know its an input issue. If it doesn't, then its a repro issue.

Cheers!

 

[famous beagle]

Ok, well. I exercised the DBX switch, tried to record, and there was no difference. Then I exercised the following pots inside the unit:

REC LEVEL HS
REC LEVEL LS
LEVEL ENCODE
VCA SYM ENCODE
PLAY LEVEL

All to no avail. It's still doing the same thing. There is some good news, which I'll reveal in a second, but first I wanted to make sure I'm understanding correctly by walking through my testing method.

So ... this is what I did:

Plug synth into CH 1 input
Switch CH 1 to mic/line
Raise CH 1 fader to shaded area (7.5)
Raise R/L program faders to shaded area
DBX was engaged on all tracks
Pan CH 1 left
Press L/1 assign switch
Turn up TRK 1 monitor switch and monitor master
Press monitor button in Meter and Phones section
Press the CH 1 record button
Plug phones in

I played a sustained synth tone and adjusted the CH 1 trim until it read 0 dB on the CH 1 meter.
I recorded that tone for 5 seconds or so.

Then I deselected the CH 1 record button, rewound the tape, and played back the tone.

Now ... at this point, I would think that the TRK 1 meter would read the same as when I recorded the signal (0 dB). But it doesn't. It reads around -10 dB, and it sounds a good bit quieter as well.

Then, I panned CH 1 hard right, released the L/1 button and pressed the R/2 button.
I turned the CH 2 monitor knob up and pressed the TRK 2 record button.
I played the same tone, and it registered slightly over the 0 dB mark on the CH 2 meter, even though I hadn't adjusted the trim at all and everything else was the same, which I thought was a little odd.

I recorded 5 seconds or so of the sustained tone, rewound the tape, disarmed TRK 2, and played back.
At this point, the CH 2 meter was barely registering anything, and the volume was very low compared to TRK 1.

When I recorded to TRK 3 through the same channel (panned L, pushed the 3 assign button, and armed TRK 3), the result is similar to that of TRK 2: Close to (if not right on) 0 dB while recording and extremely quiet and very minimal meter movement on playback.

TRK 4 was similar to TRK 1.

So ... am I correct in assuming that the meters should read the same on record and playback? Or do I have this wrong? I mean .. I know it's not correct that TRKs 2 and 3 are very low in volume compared to 1 and 4, but I just want to make sure that the meter reading and volume during recording should be the same (or at least negligible) on playback, assuming that nothing had been touched, which was the case.

The good news: The seller has offered to reimburse me for a local repair or, if there's no one around here that will do it, have me ship it back and have his tech do it. He didn't mention whether or not he'd pay for me to ship it back to him, but that's not a deal-breaker either way. If I just ship it back for a refund, I'd be liable for the return shipping charges as stated in the auction.

Anyway, can someone please confirm my understanding of the above testing?

Thanks!

 

[The Ghost of FM]

Sounds like you've gone ahead and tweaked a bunch of controls beyond what we were talking about here. Not good.

When the dbx switch was set to the bypass position and it didn't affect the channel level issues on 2 and 3, that means the switch was not the problem and it also means that the dbx calibration settings and circuitry was not the problem. But you described playing with encode level and vca trims! This was unnecessary and possibly damaging if you didn't return those trim pots to exactly were they were set before you touched them.

We also asked you to test the unit with a prerecorded tape to see if it could at least play back healthy levels. You didn't mention doing that which means you missed an opportunity to learn if the level issue is a playback problem or a recording problem.

So we have a communication problem here coupled with your inexperience to do basic trouble shooting, which is not intended to be a slag but just a statement of fact.

So, if the seller is willing to have the unit professionally repaired, go for it and stop messing with it any further as you may have already thrown it further out of whack and beyond what a semi-experienced tech can restore. And I'm referring to the dbx calibration calibration trim pots.

Cheers!

 

[A Reel Person]

Ship it to Tascam Service, in CA

Ship it to Tascam Service, in CA

 

[famous beagle]

Ship it to Tascam Service, in CA

I'm not sure I can afford that Dave. Do you have any ballpark of what we would be talking? I guess I could contact them, and perhaps they could give me an estimate?

To be honest, I had no idea that Tascam would still service these old machines!

 

[famous beagle]

I'm not sure I can afford that Dave. Do you have any ballpark of what we would be talking? I guess I could contact them, and perhaps they could give me an estimate?

To be honest, I had no idea that Tascam would still service these old machines!

I just read up on Tascam's site. There's a $40 estimate fee plus return freight charges if I decline services. I'll have to try to call to see if I can get a ballpark figure (under $100, over $200 .. what?) because I can't afford to blow $120 (shipping there and back plus $40 estimate) if the repair is going to be too much.