Audio signal tracing & schematic analysis on a Tascam 244 (I was WRONG about magnetic heads!)
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- čas přidán 6. 07. 2024
- I have made two videos about the playback circuit in the Tascam 244 before, but this is a more concise video showing me using the audio probe in a real workbench example, then showing the schematics for the circuit under test.
Spoiler alert - in the end the problem I was having (playback on tracks 2-3 was present but very quiet) wasn't anything to do with the playback circuits!
Instead I stumbled upon a fail condition of the magnetic head I hadn't seen before, that is goo from decomposed rubber in the transport getting ground into and blocking the apertures...or at least that is what I think happened?! I'd need to come across the same problem a few more times before I'm certain, and also find a way to recover a head which has become blocked like this: As I have said in other videos, the heads are pretty much the leats fungible component in these units. Maybe a bath in isopropyl would do the trick?
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CHAPTERS
0:00 Introduction
1:08 Signal tracing the 244's playback circuit with a DIY audio probe & test tape
3:36 Looking at the schematics for the circuit I just traced
8:57 The real cause of the problem- a new magnetic head fail condition! - Věda a technologie
Appreciated friend, I follow your videos and into a time line I heard what happened with the fire in your house and workshop, with the hard to swallow part of your beloved pets. Of course into the timeline this is back in the years...but I am so sorry for what it means, I can imagine...we love pets here...do have a lady cat and a dog, important part of the family....here plan to prevent a horrible situation like that...we live in an old home
Thank you for your tremendous positive energy. Once I start repairing the 238 I will keep you posted, best regards from Ky, Joe
Yesterday we lost Jeff Beck. A unique artist, that gave the guitar playing a place that no one can deny, for ever. The invention of multitrack recording, back in the old days of Abbey Road, and the iconic pieces of music after then have given to many of us a reason to breath. Rest in peace Jeff Beck, one and only
I’ll be honest, I was only passingly familiar with Jeff Beck’s work, but enough to know he was a unique and gifted musician. Sorry for your loss.
Man have ye got the patience of Job! There really is an awful lot packed into this box. I am finding I really need to keep my cool to follow the labyrinthine signal path as it weaves about from board to board. Am going to get the handbook diagrams photocopied so I don't have to keep twisting from one side of the sheet to another.
It was overwhelming when I first did it. Ive learned you can usually conceptualise each board as less than half a dozen major test points, and only need to zoom in on the umpteen other components once you've established a missing or obviously degraded signals at one of the major test points. As shown on the video, coupling capacitors bookending opamps are a good place to test for missing or degraded audio.
Thank you man, you are a blessing to those we love music and recording, simply amazing..
I do have a Tascam 238 that has an issue with its capstan
I plan to feed my mind with your capstan doings and try to repair it
Thank you, you are one of a kind sir, best regards Joe
Thanks Joe. I think the 238 is the only tascam cassette multitracker I have yet to see in the wild... I do intend to tear down repair and record with one on the channel eventually, but meantime I could probably make educated suggestions if you get stuck, happy fixing!
Thanks for your endless supply of informative videos. I had a 246 recently with what I thought was a bad erase head, it was only recording over the previous take, without a clean slate each time. While looking into the problem, I remembered the shipper had packed it badly as the top right corner was smashed. It turned out they had caused some kind of damage to the PSU, which eventually started to smoke. Forced to change the PSU and transformer, I tested it and the wipe head was now functional. I can only guess power inconsistencies caused the issue.
Thanks. Yeah I guess the bias oscillator wasn't receiving power?
@@Tetrakan I didn’t look into it any further but thanks for the extra info. I also don’t consider the magnetic heads to often be at risk of fault
Hi, I am following your instructions to the letter for replacing the belts and tires on my 244, your videos and help are invaluable, Thank You! On the right side of the unit there are two wires with a connector that aren’t connected to anything. Can you tell me if they connect to anything or perhaps they are for testing or calibration? Thank You so much!
That's the daisy chain cable that carries the power for the LEDs to the mixer channel to the right... It's a modular system, and all the channels are identical, so since there is no channel to the right of channel 1, it hangs loose. Its normal. Thanks for watching!
Good to know about the heads, and continuity is a good one
Thanks
hey man, enjoyed the video. I used a 244 to record my last album. really dig the sound of it. thanks, jeff
Thank you. Just had a nosey at your channel and now I have gear envy - Rick, Fender amp, ampeg, Rhodes - ooft!
@@Tetrakan Thanks man. I really enjoy your videos. Vey informative and thorough.
Great to see you got to the bottom of the issue and had a spare recording head to fix it! Ps are you taking on any new repair jobs in the nearish future? The rewind button has stopped working on my Yamaha MT8X II.
Hey, yeah I'll be taking on more repair work this year, msg me on fb or instagram
@@Tetrakan cool, will do. 👍
Just found your channel. It's brilliant!, SO helpful. I am just about to buy my first ever 244 and it has one issue that the seller disclosed that sounds very similar to this. I hope to be able to fix it with your brilliant videos.
The issue: Sometimes after recording on track 1, the recording isn't hearable, but after some minutes, it comes back and I can hear it again, so it seems not a recording issue but it might be to do with the reading head, similar to what you talk about here. I wanted to kindly ask (if you have time), what your advice would be to fix this issue and would it be a easyish fix? Thank you so much. Warm regards, Jon
Thanks, Jon. If the cause is what I suspect (poor & intermittent contact between the tape head and the tape) it would be an issue I could be resolved quickly and with little disassembly, BUT you'd need a certain amount of specialist kit - an oscilloscope, a 10kHz test tape and ideally a path checker cassette too. If you can find a tech who has such things and uses them often, it'd probably be cheaper to pay the tech to do it than to buy that stuff yourself? If, however, you're interested in getting into fixing these things as a hobby or to raise a bit of extra money to spend on music gear, I'd be happy to talk you through the procedure. Thanks for watching!
@@Tetrakan Thanks so much for taking the time and your estimate diagnosis, this is really helpful to know. Ah that sounds like a bigger problem (with the equipment availability) than my current limited knowledge. I'm wondering if i should not buy it. I have some funds but no experience other than watching the vids and following the manuals. The guy said he bought it a year ago and was honest enough to tell me, he said apart from this everything works, the rubbers are all replaced and its like new. Maybe I take a gamble. It's 370 euro.
IMO 370 would be fine if it'd been calibrated, but clearly, it hasn't, recently, or maybe never since leaving the factory nearly 40 years ago? If the seller can't do this before listing the item, a 100 euro drop to the price would allow a budget to have this done, but I still wouldn't buy it unless I had access to a technician who is used to working on reel to reel or cassette technology. A lot of techs nowadays don't have test tapes or know much about magnetic tape recording systems. You need someone with experience with that stuff.
@@Tetrakan Thanks this is so very helpful. It seems like too many unknowns now for me to pursue this one. I don't mind paying 100 euro but there's no guarantee they will fix it as you say, the knowledge is not easy to find. I live in Vienna, Austria so would have to find one.
Halloo, cool video chap :-) just wondering, didn’t the circuit show a lower level ie. an electronic difference in voltage but the head gap isn’t electrically connected only magnetically connected ? I’m just wondering how an electrical signal injected in the circuit could be affected by the head gap being filled with rubber dust :-) ?
Thanks for watching...what you're saying would be true if I was injecting the signal from a tone generator, but in this case the signal is originating from a test tape with the same signal printed across its entire width so if the apertures are clear the voltage induced in all four electromagnets within the head should be almost identical.
very interesting video thank you. I am wondering if it is possible to modify portastudio jack inputs to be balanced connections? I am getting a lot of radio interference noise when i plug in a dynamic mic through xlr to jack adapter. thank you!
Anythings possible, I suppose, though I'm not sure when I'd get around to attempting such a mod...meanwhile have you tried.using an external balanced preamp and feeding it into the receive port on the back of the 244? If you used a high-quality, well shielded cable between the external preamp and the rca port hopefully the.interference would be less of a problem?
Try different microphone cables first. In one case the microphone itself was the problem in my setup.. the shure sm58 had no proper ground connection inside the enclosure. Another problem could be phone charger near the 244 or noisy power line.
Very informative video, sir. Your service work illustrates the importance of replacing the rubber parts more sooner than later. Could the head be cleaned and salvaged to live another day or did you end up scrapping the "clogged" head?
Thanks! I'm not sure about the head yet, I was wondering if soaking it in an alcohol bath would clear the apertures? I'll definitely do a follow up video if I find a solution.
@@Tetrakan Maybe a soak and then let it dry. The alcohol might take any moisture with it and cause the material to shrink. I would also try a very low psi air blast or vacuum to help pull the clog material out as well.
@jamescaldwell1933 thanks, I will try that, though it may take a while to rise to the top of my to-do list: I always seem to have a backlog!
Hey man I commented recently on how your videos helped me bring a friends 244 back to life. But now…
The other night I was recording with it and I noticed track 1 started acting strange. It’s recording a low low volume. Even with it cranked thru a condenser mic it’s barely audible once recorded. When listening before recording it sounds as loud in the headphones as you would expect but once recorded the signal is very low. Popped the tape into another machine and the recorded signal stays low so I assume the playback pcb is ok. Maybe the record pcb? This machine was filthy and I changed the deteriorating pinch roller. I read in the description you said that the goo from old rubber parts could have something to do with a lower volume on a certain track.
Any recommendations on how to solve this issue I see the schematic for the record amplifier pcb having two transistors maybe one is busted? And not allowing the signal isn’t being amplified?
Thanks man. Id pay you for your time if we could chat or something about this I am very curious.
I’ve also removed the dbx from the equation because we like the hiss thanks man
Not allowing the signal to be amplified**
Hey. Transistors tend to be part of the switching system in such contraptions, with amplification provided by opamps. Most likely culprit is the electrolytic capacitors in the opamp networks. I've got some videos showing how to identify those, but a video consultation is possible. Message me via instagram or Facebook to arrange.
hey, I have the identical problem with channel 4. It records at very low volume and is very dull. I tested another cassette i recorded with another four track and the playback of channel 4 is fine.
Is yours working now?
nice find callum. i recently done a 244 for a client and god this was such an awkward heavy lump to work on. nice sounding machine when it works but an absolute pig to work on. have a 144 that i need to process too but im ignoring it for now. i dont wana 😂😂
I should warn you, the 244 is a cake walk compared to the 144!
Do you know if a Japan model 464 will work on US 120v power?
It won't work. You'd need to run an AC transformer between the wall socket and the portastudio plug to raise the voltage received by the 464's internal transformer from 120 to 240 volts. Usually, such things are pretty cheap on eBay, amazon, etc.
Thanks
Question (don't mean to condescend. I'm legit curious): wouldn't you have found the solution pretty quickly if you used a tone generator and probed it right at the beginning (after the tape head but before the first amp)?
Yes and no. I was labouring under the assumption that if a head segment has continuity in the coil, it’s fine, it took this situation to have me realise that’s not always true (a head can have continuity but still be insensitive) I wanted to document the process honestly, and it’s still a good demo for folks to watch in terms of understanding the circuit , interpreting schematics using the probe. The signal that leaves the head is really too small to pick up using the audio probe, and that part of the circuit can’t be accessed without extension wires. If I’d known the head sensitivity issue existed at the beginning of the video, the only way I can think of to establish that is swap which head segment was linked to which playback amplifier using male to female DuPont wires between the rec/play heads header and connector - different playback levels from different head segments through the same playback amplifier would prove the quieter segment was insensitive.
@@Tetrakan gotcha! I actually came back to those video because my reel to reel wasn't playing back the tape. The head might also be worn. You should do a video on replacing the tape head
@Tetrakan Have you seen op amps fail often?
Only occasionally. Like, every twentyor thirty units I fix I might need to replace a chip.
@@Tetrakan Hey thanks! After weeks of head-scratching, I fixed it today. My 488 needed new op amps on channels 6 and 7. I replaced the surrounding electrolytics too, but I think they were fine.
Tape Shaggers 🤣🤣🤣🤣
My new catchphrase!
@@Tetrakan I like it!
Your videos are an absolute life-saver! Thank you for all your time and knowledge! I'm currently fixing a 244, and everything is now working fine except for Channel one is nothing but severe ground hum when set in Cue mode. I can monitor the input just fine, but as soon as I press play, record or pause....BZZZZZZZ! And I've noticed that it gets louder whenever something comes close to the play/record connectors on the record board. I've resoldered the connectors just in case it was a faulty wire, but no joy! Any help would be much appreciated.
Cheers then!