Dead Teac 80-8 - Help with diagnosis?

[Tired Eyes]

Hi, I'm new to the board and, hopefully, to recording with tape.

I have a Teac 80-8 in rough shape on loan from a friend who's selling it, trying to determine how much work it needs. I guess this is a typical 'is it worth fixing' post.

The capstan motor works, but other than that, no action.

The fuse 3rd from the right looking from the front of the machine, labeled F6, was blown. The blown fuse I removed was 10 amps, but it was only supposed to be a 3 amp fuse in there. I jumpered the fuse contacts for a second with an amp meter and it was drawing 12 amps. So there's a clue.

The lights on the VU meters came on when the fuse was jumpered but the transport controls still didn't do anything.

There's also a wire unsoldered hanging right next to a 4 terminal can capacitor on the upper right of the unit looking from the back. Although it looks fairly obvious where this belongs, I didn't want to connect it without having the schematic to be sure.

Does this give anyone any clues? He's asking $150, but I don't want to pay that if I'm going to have to start troubleshooting the control board.

Does anyone know if the service manual for this unit includes a complete schematic? I found a different Teac manual on the net but it only had a 'simplified' one at the end, which would do me no good in fixing the control board.

At this point my gut feeling is offer $50 to open this can of worms, otherwise let it become someone else's problem.

[CurtZHP]

How are the heads on it? Not much point in fixing it if the heads are shot, as they will certainly cost more than what you'd sink into it fixing what appears to be a power supply/control issue.

[Judas Jetski]

I say go with your gut. You don't want to have to try to learn how to record to tape while also trying to learn the ins and outs and peculiarities of a uniquely hammered tape deck.

[lassoharp]

12 amps is an awful lot of current - would probably cook nearly every component in it's path save for maybe the big brown power resistors.

Hopefully the very big mistake of someone using a 10A in a 3A slot didn't already fry a lot of other things.

First thing I'd do is check all the boards you can see for burnt components. Burnt resistor smell is a smell that will remain strongly for months afterward. If you smell it and can't see where it is you'll have to go farther than removing the back panel.

That big cap you're referring to I think, is the motor start/run cap. Do a resistance check of it with an ohmmeter - look for short or low resistance.

Usually that kind of current draw means a dead short somewhere in the PS. I believe those caps(roughly 2000uF or so) are located on the board situated horizontally in the middle (looking in from back) Check those for shorts.

I've owned an 80-8 for about 14 years - great workhorse of a machine. I had a transport problem similar to yours that turned out to be a misseating of the brake solenoid on the take-up reel. Works it's way loose over time and causes all the transport functions to fail. Easy to fix though, only takes a screwdriver.

But before checking that you should put a 3 or 2 & 1/2 A fuse in and power up. Pay close attention to how quickly and in what manner the fuse blows. If it's still blowing quickly you'll need to locate the short before proceeding.

Here's the only place I know of online for free 80-8 manual/schematic

http://www.audioschematics.com/tascam.html

If you get the short located and fixed I can tell you how to adjust the brake solenoid.

[Tired Eyes]

Thanks alot! I was able to download the schematic and investigate the problem further. I take it you're familiar with this unit?

Turns out the short is in the section of the power supply that controls the 5V DC to the control board. The blown fuse carries 13V AC to the power supply where it's rectified to 13-14.5V DC through diodes D1 through D4 and caps C1 and C2.

I checked C1 and C2 for shorts and no dice - could they be partially shorted? Whatever the short is, it took out all 4 rectifier diodes so I'll replace those. Then just check components one by one until I find the bad one? Would the IC be suspect?

At any rate this is good news because the power supply issue explains the total fail in the transport and the stuff to fix it shouldn't be expensive.

[lassoharp]

Good work! Are C1 and C2 the can types? If they've gone bad(to shorting condition) it's usually an all or nothing thing. You'd have to get under the PC board to check them.

My next guess would be the voltage regulator. I'm not sure of it's exact location or it's physical ID. Many VRs look like small power transistors with a metal heat sink tab. I've had other equipment where a failed VR was the problem. I came across a post over at Home Recording that mentioned the specific VR in the 80-8 being a possible cause of transport failure. I believe the forum member who posted it was 'The Ghost of FM'. I thought I'd mention that as a reference in case you can't locate the VR in the schematic.

If no caps are showing shorts then yes, replace all the burnt diodes and/or resistors. Also take a close look at all the components in the PS- if they're using any small signal transistors there, there's a good chance those got taken out as well - easy to check those with DMM.

[Tired Eyes]

There's one can and one small orange disc type, in parallel. I removed both of them to check. They seem to be doing their thing just fine, resistance increases as the charge builds up from the voltage from the tester.

I have the part number for the voltage regulator and checked online, it seems to be in stock at the electronics depot near my work. I'm headed there shortly to pick up one of those, some diodes, and maybe some of those transistors just so I'm good and loaded up for the weekend.

This is really my first foray into transistor gear. I'm pretty embarrassed, but I don't even know how to test a transistor. I know I have it in a book somewhere, I'll figure it out.

[Tired Eyes]

I just put the voltage regulator IC in and BLAMMO! Everything works!

Of course, I have yet to investigate the whole other side of this box, you know, the audio part.

Thanks again, you're the best.

[lassoharp]

Awesome! Glad to hear you got that thing going. Man that was fast - sounds like you've got the knack for DIY.

Good to hear that VR was still readily available. Common for 70's SS stuff to be obsolete.

One thing to keep an eye out for on the audio end is the audio cards -accessed from the front. Sometimes they need to be reseated - one symptom is weak playback output with high end severely rolled off. Probably a good idea to give all the edge connectors on the cards a little deoxit cleaning.

Other than that mine has been a dependable and relatively trouble free machine compared to my MCI and Scully.

Enjoy!

[clean_and_humble]

so what was the outcome of this machine? Are you using it now? How does it sound?
Any recordings done with it? A friend gave me this machine and yes it is not working.It powers up but none of the lights work on it and I do not think the capstan moves when the tape lever is put into play mode.I am not the greatest at talking tech and not to good at fixing things but reading this post of yours I think mine might have the same problem.I think this will inspire me to open it up and investigate it more.I have one silly question about this machine Does each channel have transformers? Is that why the machine is so damn heavy? Transformers on rca inputs ? That seems odd to me but I do not know anything about this stuff trying to learn.Thanks for posting that link I wonder if you can get the schematic there still.I posted about my 80-8 on here I will post any progress I have with my machine on that post.I am also looking for a schematic for my Viscount Bahia organ that I took apart to make a drum machine out of but stupidly did not label the parts I was disconnecting so now I do not know how to put it back together.I also have a post about that on here


Any help is appreciated

[Tired Eyes]

I just got it fixed and am looking for some tape to test it with. I also had to fix a motor issue which turned out to be the motor was wired wrong by the last guy who had it. I'm sure he meant well, but his repair efforts sure ended up making my job harder.

To get you started, I'd suggest measuring voltages on the power supply board. On the inside edge of the circuit board there is a row of terminals labeled with the voltage they're supposed to be at. Check that with a volt meter and that should tell you where the problem area is. It looks like your problem is similar to mine.

[skywavebe]

Hi Tired,
That machine is pretty old and has a lot of relay type stuff that can go wrong and give you headaches. I worked on a number of them. Once you get it into working condition it is like a tank. If you need further help do not hesitate to give me an E mail directly.
skywavebe@sbcglobal.net

I was a Lead Tech at Teac in Chicago so I know something about them.

[jshirks]

There's a lot of very good advice that is all right on. I am 98.9% completely rebuilding one of the early production models (serial 129.) Even compared to a studer 2" 24 trk, this little machine can pack a punch particularly if you know how to tweak it out. I got the machine for around $100 half working, that sounds about right and since have put almost $1000 into it. After two months of operation the machine has already paid for it's repairs. Go back to the first thread and re-read what the first guy wrote. "If the head-stack is good..." If your headstack is shot and you can't get a hold of one there is no point. I'm fortunate enough to be in Nashville and have already claimed all of the Teac heads in town. If got that covered, can solder, and have enough technical troubleshooting common sense, the Teac is a great project.

*** Any dangling wires that are connected to anything, need to be connected something (preferably the right something:)***

First get a service and operation manual, once upon a time I found one on eBay for $20. It came as PDF's on a CD, the best thing I ever got. Let me know if you need Schematics, I have them all.

Recap the entire machine ($50-60,) there are at least 400 electrolytic capacitors that are getting close to thirty years old. They are dry, a lot of these are audio path and will effect frequency response.

Start with the power supply, MAKE SURE ALL VOLTAGES ARE TO SPEC. The power supply can be completely re-built for under $100 (that's probably cheaper than the time spent of trying to find issues unless they are obvious.) DON'T REPLACE ANYTHING ELSE IF YOUR VOLTAGES ARE NOT CORRECT. If problem in the supply have toasted other components else where in the machine, you'll only toast them again...

After that, any switching problems are in the Control Board logic IC's or the Channel card relays. the relays can be manually actuated and check for continuity. If they are good and not switching, the Logic IC's in the Control Board are Frozen, burnt, or simply have a broken pin.

Look for toasted diodes, bad pots, and crackling op-amps on the audio cards. It's best to have a few spares. I haven't tried putting a modern op-Amp in the amp stages. there are mixed reviews about the JRCs that were put in it. That's next up:) Hope some of this helps. -J

[jshirks]

Here's two things I forgot to mention.

1) The LED mod to get rid of the bulbs will save some bulb changing.



2) This guy wanted $150 for a remote for the unit, I told him there wasn't a single electric component in it except two LEDs and made one from a Nintendo controller. Any controller will work as long as it has push buttons that can gotten to and cut out of circuit.

[Judas Jetski]

That Nintendo remote has gotta be the coolest thing I've ever seen.