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Old 8th Nov 2008, 1:02 am   #61
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Quote:
Originally Posted by Michael Maurice View Post
Leaving a machine on for several hours should not in itself cause it to fail.
I completly agree with that sentiment Michael. However, this machine is old, it's been subjected to numerous power up and off while I've been doing the testing and 40 year old caps and such have a tendency to get tired.

Les, the belt was goo when I got it, the first thing I did was to clean up the mess and install a new one. FF and Reverse still work fine. I'm thinking some more fried caps because it's got that funky, not burnt, but strong chemically smell coming out of it. I'll work back from the capstan motor and if I get stuck (very likely) I'll be again calling on your good services.
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Old 8th Nov 2008, 1:35 am   #62
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Hi Marty, The Servo Motor supply is made available by fuse FS901 3 Amp. It is rectified and smoothed then fed to the other micro switch activated by the right hand tension lever. This is why the servo motor should only run when the arm is moved from its rest. The servo motor return is via the transistors mounted on the servo board. A feedback coil in the servo provides feedback for speed control.
The smell you are noticing could be just dust being heated by the large enamel coated resistors used for current control in providing forward and back tension on the reel motors, I get the same from mine as it is not used regular enough to keep the dust burnt off .
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Old 14th Nov 2008, 9:43 pm   #63
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Hey, Les

Been out of pocket for the last week with a bad cold. Hard to stick probes into electrified components when you might sneeze at the wrong time.

Thanks for the info, and yes F901 is the fuse that keeps blowing. Funny thing is when it blows, the on/off switch must being shorted or bypassed in some fashion because the machine stays powered up in on or off. Let's put it this way, it was a shocking discovery.

I was able to take some measurements at the Capstan Servo Board between the fuse blowing up. There are 3 sets of wires coming from the motor to the board. The largest wire contains 3 wires, a bare one which I am presuming is ground since it measures nil, and two others. On those wires I measured 32v on the white one and about 1/2 volt on the blue. The schematic I have offers no voltages anywhere on it so it's hard to tell what I'm seeing. The other two brown wires measure nil so I'm thinking they also go to ground but I am unfamiliar with motors of this type, so I really haven't a clue.

Do you think that those safety switches (S902 and S901) might be the culprit, and if so how do I test? I presume these are the two micro switches which operate the capstan solenoid and auto shutoff on the right take up arm. Any other thoughts you might have would also be appreciated.
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Old 15th Nov 2008, 3:09 am   #64
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Hi Marty, well you do seem to be having problems. I have attached a couple of jpegs, one shows the safety switches operated by the right hand lever. The wire track shown in Green is the STOP line switch and grounds the stop line when the lever is not raised. The other one, coloured Red is the supply to the servo motor. This operates opposite to the other one, i.e. is open circuit until the arm is raised. The fuse should not blow with the arm not raised as the supply should not be going anywhere unless the microswitch has badly failed and the internals are shorting to the metal cam that operates it.
If this is found to be in good order, I can only suggest you check for short circuits on the feed to the servo board as indicated in Red on the other jpeg. This is new territory for me also, I suspect the brown wires may be the feedback winding that I have shown in Purple. You could check the transistors in the ground return but I would not expect them to blow the fuse, rather make the servo motor go flat out with no control. The third plain wire is probably an earth wire for the motor case. The motor is sure to be a DC motor with a commutator and maybe, just maybe, the earth wire works in conjunction with filter capacitors in the motor? This is pure supposition as I have never taken this motor apart but if you find that the fuse blows due to excess current in the motor, then one of these capacitors (if they exist?) may be at fault. I hope you find a short circuit somewhere else though, a solder splash or something shorting the supply somewhere. I really have my fingers crossed for you that you dont have to disassemble the motor, make that your last move if you cannot find the cause for excess current elswhere.
Les
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Old 15th Nov 2008, 9:44 am   #65
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

I saw this posting last night, what Les says now makes sense. If Les is correct and that the plain wire is just an earth for the motor case and possibly filter capacitors, then you could disconnect it at the servo PCB, connect a voltmeter between it and ground, replace fuse 901 and switch on. If all is well, there should be 0V on this wire, if there are any volts, then it would point to a leak or short within the motor.

Les, do you concur?
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Old 15th Nov 2008, 2:15 pm   #66
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Yes Michael that would be a good check if there are no shorts found on the motor supply after isolating it from the rest of the circuitry. By removing the earth wire from the motor, it would remove a return path if a suppressor capacitor in the motor were defective, assuming of course that this earth wire is not connected to the motor body. If it is a plain uninsulated wire it may very well be attached to the motor casing and thus the fault current will go down via the motor mount.
My previous post assumed that the servo board was separate to the actual motor but I cannot find any drawings of the board and the circuit diagram shows no connectors between it and the actual motor. I was beginning to think that the board may be fitted inside the motor itself but the service manual shows the board fitted above the power supply board so that's a relief! Without stripping down my own machine I am like a fish out of water here as I have never had to fault find round this area of the circuit.
With regards to the mains switch, I am puzzled that it is not working at times and makes one assume the fault current is partially welding the contacts. Looking at the mechanics of this switch I would hazard a guess and say that was unlikely. There is a capacitor placed across the switch contacts for suppression and this might be worth a check before suspecting the switch.
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Old 16th Nov 2008, 5:59 pm   #67
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Well gentleman, following your advice I popped in a new fuse and it does not blow when when the shutoff arm is not engaged. Figuring the power supply was ok, I then did a fair amount of testing along the sensor board circuits and couldn't find anything obvious. I did swap out 2 caps in the circuit you outlined for me Les, but had to replace the .033 (C2) with a .047. Figured it was close enough for testing purposes. Fired it up and no change. With the arm engaged the take up reels move a smidgen then stop and then forward and rewind stop working.

Les, your thought that the middle wire was grounded internally made sense to me, so I unscrewed the capstan motor and it felt like it was binding slightly, so I took it apart. Dangling from the bushing cap was a thin wire wrapped around what looks like a ferrite rod. It looks a bit burned where this rod used to reside. I've attached a picture and it does show the middle wire grounded to the motor body, the blue wire going directly to an internal cap and the white wire going to the rod where the ferrite rod was attached and hence to the other side of the cap.

Now I know we are getting into the land of the esoteric here, but I do have several questions:

1. The white wire was were I was getting the readings of 32 volts at the sensor board. This motor is rated for 24volts, (7watts). Do you think the high voltage caused the short in the motor or instead did the motor problem create the high volatge readings at the sensor board?

2. What is this rod. Is it an oscillator or magnet of some sort to set the 60mhz cycle? If so, does it require a specific amount of copper wire turns to set this properly? The reason I ask is that I've found that destranded desoldering wire is about the right thickness so I was thinking of rewinding it and giving it a whirl.

3. Should I super glue the end of the rod to it's post or is this type of thing designed to vibrate?

The reason I ask is that finding one of this motors is gong to take a long patient search, and there's little reason to rebuild this motor if I'm simply going to blow it up again with too much current.

I can understand if you don't want to play anymore, but the economy is bust and I can't afford to ship this out to someone who knows what they are doing.
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Old 16th Nov 2008, 9:04 pm   #68
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Hey Marty your description of events upon switch on are a bit puzzling.
When you power up the machine nothing should move. However, when you lift the right hand lever ONLY the servo should run, there should not be any movement from the reel motors at this time. Is this correct?
I just had a terrible thought that you were trying to engage REW and/or FF and for some reason the brake solenoid was not releasing the brakes? This would cause a higher than normal current to be drawn and thus blow a fuse. Does the capstan rotate freely even with the machine off?

I just want to make sure we are not blaming the servo motor for a fault that may be existing elsewhere, keep all your options open here .
32V may appear a bit high but will no doubt drop somewhat when the supply line is loaded. The rod looks like a filter choke but for what may I ask.
Well the motor is a DC Servo which means that although it performs the task as a motor to drive the capstan, it also contains a DC generator whose output voltage is proportional to the motor speed.
The output of the generator is fed to a comparator on the servo board where it is compared to a voltage provided by the speed adjustment controls. If the generator output is lower than this voltage, the comparator will keep the transistors in the servo motor turned ON. When the motor reaches a speed where the generator output is greater then the control voltage, the transistors are turned OFF. Thus the motor speed will be under the control of the voltage provided by the speed adjustment variable resistors. Now the filter may well be for the generator DC output as this will also have commutator type noise on it and that would not be good for reliable switching by the comparator. The fact that the wire on these ferrite slugs is rather fine makes me think it is the DC generator output.
The burnt appearance may just be varnish applied to keep the winding together, you can't use the wire you suggest as it is not coated with insulating enamel. You should be able to replace these if necessary using ready made ferrite chokes, you can buy some as high as 47mH and yet are as small as a quarter watt resistor. The choke should be held secure Marty so a dab of super glue will be fine. I would imagine that by spinning the motor spindle you should see a small voltage appearing on the feedback lines, my guess it will be the brown wires though I would be expecting to see some form of identification with respect to polarity. For if the brown wires are the feedback ones, the servo motor will not be controlled if the wires were round the wrong way.

Can you not disconnect the servo motor and apply a separate DC supply from an adjustable power supply? You could use current limiting to protect against excess current being drawn and at least you could be certain that the servo either works or does not work outside the main circuit.
Cheers
Les
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Old 16th Nov 2008, 10:18 pm   #69
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Much to absorb here Les.

First one clarification, when I put the arm under tension and hit Play, then the take up reels start moving very slowly and just for a moment. The capstan solenoid engages at the same time but the capstan does not spin because the capstan motor is not spinning. After that if I hit stop and try FF or RW the take up reels do not function. However, if I leave the lever down, FF and RW work.

As to the motor itself I think a large flashlight battery will do the trick since my variac does not have a DC function. I presume I just tack a wire across where the choke was for testing purposes. I'll also test the brown wires and then methinks I'm going to have to order up a choke before I go any farther.

It's days like this I wish I had an electronics store in the area. I hate having to wait for online orders to ship.
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Old 16th Nov 2008, 11:47 pm   #70
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Be aware Marty that the chokes may be for the tacho output and not for the motor supply. Placing any supply onto the tacho motor windings may do damage. Trace the actual servo motor wires back to the microswitch (or alternatively the servo board connector pins 9 & 10) for your positive connection and to the servo board driving transistor (collector of Q4).
You should see some turning of the motor.
As there is no motor rotation at present I think an independant test like this will prove if the motor is the culprit. It's a pity if it is but if you do prove that there is a short circuit inside it then you really have nothing to lose in attempting to find the fault internally. Could be just a whisker of wire, defective noise suppressor capacitor etc. Do some web searches for Teac spares, you may be lucky.
All the best
Les
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Old 17th Nov 2008, 12:02 am   #71
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

If you disconnected the motor wires from the servo board and connected them to a 9V battery, such as a PP3 the motor should rotate. Do not connect the battery to the brown wires, but to the blue and white wires. If the motor rotates, then its likely to be ok, if not then you've got a dud.

If the motor has failed then finding a new one may not be easy, but youre more likely to find it in the US. try googling Teac A3440 spares and see what you come up with.
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Old 17th Nov 2008, 11:44 pm   #72
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

It looks to me like the motor is toast.

All I had handy was a 9volt battery, like the kind you use in smoke alarms, but it should have started it spinning. No joy, with or without bridging where the choke used to be.

Upon closer inspection there is a plastic shield between the motor winding and where they connect to the points where the winding wires go (sorry I can''t describe it better than that). Part of this plastic sheet has melted onto the windings.

That cap in the motor seems fine, but I will also desolder that and just bridge with wire to see if there is any difference, but I kinda really doubt it.

Looks like a long patient search to come up with a motor is now in order.

Although, this motor is actually a motor contained within it's own housing which is then contained within an outer housing for isolation (rubber pads at each end) and for mounting. Could you provide a more exact description of this type of DC motor? Maybe I could come up with a suitably sized substitute. Just casting about, of course.
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Old 18th Nov 2008, 12:51 am   #73
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Try these folks Marty

http://www.daeinconline.com/parts.html

You cannot just replace with an ordinary motor as you will have no speed control, hopefully you will find a site in the States able to assist you.

Good Luck in your endeavours.

Les
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Old 19th Nov 2008, 2:11 am   #74
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Thanks for the kind words Les. and your contributions, Michael.

I have a friend who may have a "hanger queen" with a working motor, so all is not lost.

In any event, thanks to the longevity of the web, this type of thread (I'm very active on the Klipsch forum, so I've seen this before) will pay dividends to other hobbyists over the coming months and years. Certainly, several important lessons for dealing with these Teac's are now readily accessible to those scratching their heads over what to do about a rig they already have, or have recently acquired.

Next up, a Tandberg 64. I've already got some clues from this forum, but I'm sure I'll still end up with a question or two.
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Old 1st Dec 2008, 9:23 pm   #75
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Hi gentlemen
I have one question about an A3440 S, I have a problem with the START and I thing it is an electronic fault, but how I can come close to control pcb and work with this? It is a lot of cables around.
Thanks in advance
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Old 2nd Dec 2008, 11:27 pm   #76
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

I suspect that the 3440S is very similar to the a3440. On my A3440 you will find 3 screws on each side of the rear of the deck just below where the power control board sits. If you remove these you will be able to lower that panel and give yourself more working room. The cables coming into the rear of the board can be gently removed. There are also two other small plugs, one to the main circuit board and one to the power board that can also be removed. Then there is a screw and a plug at the back of the board which can be removed.

After you have done this you can gently ease the entire board out and remove the two smaller cables I mentioned. This will give you access to the entire power control board for testing.

First however, spend a few minutes reading over this entire post. You may just have a sticky capstan lever.
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Old 3rd Dec 2008, 1:31 am   #77
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Here's a link to a very good how to on how to deal with Teac pinch rollers:

http://www.vintage-electronics.cc/teacfix.pdf
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Old 3rd Dec 2008, 11:04 am   #78
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Default Re: TEAC A3440 /REVOX A (HS) 77 - troubleshooting help please

Thanks Thebes1.
I think the "S" version is not the same as the ordinary!
Your description is not correspond to this RtR.
Yesterday I make an attempt, together with a friend who is Senior mechanical engineer and very ingenious to find solutions, but we gave up!
The problem is electrical, not mechanical, the capstan mechanism is moving free!
Thanks for yours effort gentlemen
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