8mm Forum: Bauer T450, soundheads not engaging, servo electronic failure

This is topic Bauer T450, soundheads not engaging, servo electronic failure in forum 8mm Forum at 8mm Forum.

To visit this topic, use this URL:
https://8mmforum.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=001346

Posted by Jan Bister (Member # 332) on July 31, 2005, 12:49 PM:

Just wondering if someone (Rick etc.) can help me with an electronics problem? My Bauer T450 will no longer engage the pressure pads for the sound heads when trying to play sound film, it behaves as if the sound mode switch were permanently stuck in "silent" mode (which prevents unnecessary head wear with silent movies).
The projector is servo-controlled, that is, a small motor turns the shaft that would normally be turned by a manual rotary switch. All the positions are correctly "locked onto" by pressing the electronic FWD, REV, REW and STOP buttons. There are two different positions, one which engages the pressure pads and one which does not, both of these are switched between by means of the sound mode switch (which also signals the servo motor).
Problem is, one day I messed around inside the projector with a screwdriver (stupid me!!!) and *ZAP* sparks flew and from then on the sound head pressure pads would no longer engage. I believe I shorted a diode and a rather beefy resistor together momentarily. I don't have access to any wiring diagrams or such, and was wondering if I could just try bridging the (assumed dead) diode for starters and see what happens.
Any ideas? I suppose I could just turn to Wittner-Kinotechnik in Germany but the cost of shipping the projector there and back alone would be prohibitive...!

Posted by Rick Skowronek (Member # 385) on August 01, 2005, 09:08 AM:

Oof, Jan. The old slippery screwdriver in the electronics trick. That does tend to muck stuff up pretty quickly. Just ask me. I've done that a few times before and it's usually not pretty.

Just off the top of my head, I would say the pressure roller and head pads are activated by a solenoid under control of the forward and, possibly if that feature is on yours, reverse. As well, it is primarily controlled by the sound/silent switch. The key here is, since the entire unit is basically servo controlled, does this solenoid have a transistor circuit driving it or is it just a switch arrangement supplying DC through the Forward switch and then through the sound/silent switch. Typically, most servo/solenoid systems have a separate DC supply for that piece just to keep the surges and noise out of the rest of the electronics. If, however, the rest of your servo system is operating, then that DC supply is probably okay and it's the circuit that feeds that specific solenoid.

Now we reach the crystal ball phase because without a circuit diagram we're just throwing stuff against the wall to see what may stick. I'll presume you've found and checked all fuses. The Germans typically fused their equipment designs pretty well. Now comes the hard part. Tracking the wires from that solenoid back to the circuit area to see what you can see. If indeed this is a transistor controlled circuit, the driver transistor for that solenoid is a pretty good suspect. The solenoids are usually pretty bulletproof. Since your quick short didn't wipe a power supply fuse (you've checked right?) we have to assume the worst and say a piece of circuit got creamed.

I'm hoping someone on the forum has a circuit diagram because without one it's anyone's guess as to what blew. I WOULDN'T recommend shorting anything to try and see if that brings it back. You could total more parts to the circuit and make it that much more difficult to repair.

My first suggestion is, by hook or crook, see if someone here has the diagram and, if not, see if you can finegal at least the circuit diagrams out of the German repair folks. A good electronic scan of them would be fine. If all else fails, I could look at it undocumented and perhaps track the wayward piece but that's really getting lucky since typically a wiped transistor or other part is very hard to classify or even find without the diagrams.

Let's see what the European contingent may have to say.

Rick

Posted by Jan Bister (Member # 332) on August 02, 2005, 12:19 AM:

Wow, that was very enlightening so far, thank you. [Smile]

I could indeed try and ask Wittner-Kinotechnik etc. if they have circuit diagrams they can scan and email to me.

Just one dumb question I have right now: what is a solenoid? [Eek!]

Posted by Rick Skowronek (Member # 385) on August 02, 2005, 01:26 PM:

Hey Jan,

No such thing as a dumb question. Basically a solenoid converts electrical energy to mechanical motion. It is nothing more, typically, than a large coil of wire with a steel plunger in the center. When energized it pulls the plunger back into the coil. Attached to the end of the plunger is whatever you want pulled/actuated, etc. In your case it would be the head pads and probably the pinch roller up to the heads and capstan shaft. The picture below shows a couple of examples although there's multitudes of sizes and styles.

Rick

Posted by Jan Bister (Member # 332) on August 02, 2005, 07:39 PM:

Ahh, those things... Okay. No, there are no solenoids in this projector anywhere. The soundhead pressure pads are just one of many mechanical pieces that are all moved in and out of position by a single long rail with, let's call them, hills and valleys... That rail moves left and right, settling into a number of positions between either end, and its movement is controlled by the servo motor (and electronic touch keys). Basically everything works exactly the same as if the projector had a manual rotary switch (like most others do), except there's the motor turning that switch instead.
In other words, if I somehow disengaged the motor and did turn the switch by hand (causing the rail to move)... I could re-engage the pressure pads. The problem is that whichever component is supposed to sense the position of the sound mode switch and signal the servo motor accordingly is no longer doing so. Is this making sense?... I could probably help out with some webcam pictures to explain it better...

Posted by Rick Skowronek (Member # 385) on August 02, 2005, 08:13 PM:

Ah, I'm beginning to get the gist of your unit. Interesting that they'd put a motor in to drive the main functions but who am I to argue. So, in essence, you're saying that this rail moves and mechanically engages all the different functions. Is it just not moving at all anymore, like in the servo motor is dead, or is it just not going far enough to push up the pads for sound? It may have been the sensing unit for it to know when it had gone far enough to activate the pads. This kinda sounds like a position sensing circuit via a microswitch if it's just not going far enough to go into sound mode.

A picture or two would be helpful.

Sorry for the misinterpretation.

Rick

Posted by Jan Bister (Member # 332) on August 07, 2005, 11:54 AM:

No need to be sorry. [Smile]

Here's what it looks like - I tried my best to provide you with close-ups of all the details...

You can see it really well in the second picture: the servo motor shaft + cogs, the rail (below the 2nd sprocket and film guide)... this should give you an idea of things.

I did email Dieter Faelker of www.faelker.de by the way (his site specializes in film-to-video transfers using modified Bauer projectors). He's been extremely helpful before with finding a film gate pressure plate for my model, so I asked him about the circuit diagram etc., let's see what comes of it. [Smile]

Gee... if I'd known back then (when I was a teenager and got this projector NEW for my birthday) what a wonderful machine it really was and how valuable it would be one day - not to mention knowing now what I didn't know then - I would have taken MUCH better care of it! But it still runs, and I'm not giving up on it.... [Cool]

EDIT, I keep thinking of more things to add here [Big Grin]

and you seemed surprised that they'd control all the mechanical functions via the servo motor. Actually that's what enables the projector to automate much of the stuff it does - for example, it senses when you insert film and switches itself into thread mode, and when you use the digital counter and programmable recording feature, the projector switches record mode on and off by itself and, after recording finishes, reverses the film to return to the beginning point. It even stops projection in case the film jams inside the path and goes into rewind mode! (Actually not a good thing, so I've since removed that part) [Wink]

Posted by John Whittle (Member # 22) on August 08, 2005, 08:54 AM:

Jan

If I understand this now, the motor does work and the cam rail moves and gets you all functions except closing the sound pressure plate.

Then I'd check two things:

1. Is the cam follower that pushs the pressure plate into position on it's rail or is it broken.

2. Is the cam rail itself "out of time" meaning is it pushed so it doesn't travel far enough to engage the cam follower?

This may be a mechanical problem, not an electronic problem.

John

Posted by Jan Bister (Member # 332) on August 08, 2005, 10:51 PM:

Good advice, but the answer to both questions is no. I'm 100% positive that the problem is of an electronic nature. It was working just fine right up until I shorted things on the main board - and also, (for some odd reason), the 'silent' position of the cam rail is at the extreme edge while the 'sound' position is just a bit before that. Meaning that once you thread a film and then go to regular 'forward' projection mode, the soundhead pressure pads will momentarily engage while the cam rail is still moving, then come back down again. The way it's supposed to work is that if I switch from 'silent' to 'sound' mode, the rail moves back a little bit and the pressure pads re-engage. Well, that no longer happens (sniff).

I'm still waiting for a response from Mr. Faelker, but if nothing comes of it and I can't solve the problem any other way, then I guess I'll just have to push the pressure pads up manually and keep them stuck in that position. [Eek!]

Posted by John Whittle (Member # 22) on August 09, 2005, 08:40 AM:

quote:
The way it's supposed to work is that if I switch from 'silent' to 'sound' mode, the rail moves back a little bit and the pressure pads re-engage. Well, that no longer happens (sniff).

So if you go into 'silent' mode now, the rail moves all the way to the end and the sound gate closes and opens?

If so, can you determine how the 'positions' are determined? is there a wafer switch or some other method of multiple contacts that are opened and closed or is it all microprocessor controlled? If it's the first, you should look for damage from your screwdriver that shorted something across a solder path and made a short circuit. If it's the latter, it sounds like it would require a new microprocessor. I don't know the age of the projector, but most of the 16mm stuff that was built with the motor driven positioning like the Elmo and Eiki slot loaders had the same switchs and just replaced the knob for a motor.

I'd really suspect either a bad switch or a short from your "sparks".

John

Posted by Jan Bister (Member # 332) on August 09, 2005, 08:22 PM:

It's all microprocessor-controlled... but the servo electronics that control the motor are on a separate daughterboard, and I wasn't anywhere near that with the screwdriver. Plus, I caused the short between two components, rather than on the bottom where all the solder spots and pathways are.
And somehow I can't imagine that the processor chip itself was damaged since everything else works just fine - if it had been damaged then (so I'd assume) nothing would work anymore, the touch keys wouldn't trigger any of the projector's functions.

Circuit diagram... I need a circuit diagram [Mad]

Oh, and you asked "So if you go into 'silent' mode now, the rail moves all the way to the end and the sound gate closes and opens?" The answer to that is yes.

Posted by Rick Skowronek (Member # 385) on August 10, 2005, 09:36 AM:

Hi Jan,

Your pictures were great. Looks like an explosion in a robot factory [Wink]

. Carrying the thought process on a bit further, one question. How old is this unit.Sounded like you've had it for quite awhile. Chances of it being microprocessor controlled are extremely remote. More than likely some fairly sophisticated logic. There is obviously something or things on the servo mechanical rail that sense where it is so that the various inputs (soft switches, film sense, sound/silent switch, etc.) tell it to actuate to a certain position and stop there till the next command, yours or the projector's). The schematic will tell us what these are and the type of logic and paths they have.

Your short probably removed a component of that position sensing circuit. Specifically the one that tells it the rail got to the right spot to push the head pads up against the heads and to stop there. Since it doesn't have that "sense" anymore it keeps on going till it gets to the next position sensor that shuts it down from going any further. Probably, from the sounds of it, the end of travel sensor that prevents the servo and rail from trying to keep pushing it past the end of it's range.

The key here is what senses that it reached the "pads up" position and what did you blow in that circuit. It could be the following, not necessarily in any priority order:
1. the switch that senses the position (I presume it's fairly dainty and small).
2. The piece of logic itself that watches that input. This could be an integrated circuit, transistor or combination. I have seen specific inputs of logic circuits get wiped without taking any other part of the circuit with it. That input could've acted like a fuse.
3. There may be other components leading from the sense switch to the logic (resistor, diode, etc.) that could've opened with the short.

I suspect when you shorted you were in the vicinity of or in that sense circuit. The short put way too much voltage on that input and did it's number on whatever in that total sense/logic circuit. Obviously, the schematic will make it all academic as to the guessing but, if that doesn't pan, it still can be troubleshot. Where you run into difficulties is replacing the defective piece if you can't tell it's specs (transistor, IC).

Let me know.

Rick

Posted by Jan Bister (Member # 332) on August 10, 2005, 08:50 PM:

Rick,

wow! [Smile]

I think you're just about dead on with everything you've said. I do think I've seen a few IC chips here and there, but you could well be right in that whichever circuit takes care of the sound head pressure pad position sensing is made of discrete components (diodes, resistors, transistors). You're also right in that there are switches on both ends of the turn radius of the motor shaft that prevent it from going too far.
But to answer your question... I got this projector new in 1986, I think...and it had been manufactured in 1983 for Bauer by Silma of Italy. It was one of the last series of projectors ever made/sold, in fact the little brother of the studio-series T5xx and T6xx machines. Its "sister," the T430 Servo Stereo, was identical to the T450 except it had an additional stereo record/playback setting and a stereo power amplifier with two speaker-out jacks. It also came without the digital frame counter and programmable recording feature that the T450 has, but it was the same in all other aspects.
Really, I think the T450 is a fabulous machine with some awesome features... its only major drawback being that it was built without a top sprocket (pulling the film in was done via the claw mechanism). I've taken care of that part by constructing my own sprocket mechanism ... and yes, I've been meaning to document that little feat of mine ever since I first joined this forum... it seems things are coming full-circle here... someone remind me to do this on the weekend. [Big Grin]

Posted by Rick Skowronek (Member # 385) on August 11, 2005, 09:32 AM:

Jan,

Wow, putting your own top sprocket in. You're right on the feat part. Would be interesting to see how you accomplished that.

Anyway, let me know if you get a schematic for the beast. Obviously worth saving. Let's just hope it's not an unobtainium part. If you can't get one, we'll have to see what you want to do next. Could send it my way I guess and I'll see if it's something obvious and repairable. Been fairly lucky so far.

Rick

UBB.classic^TM 6.3.1.2