Need help with Circuit

[ZTatZAU]

I can't add much to this conversation, but remind me to never piss ZTatZAU off.

Hi Sceadwian... <Now that thar's funny!>

Let's just chalk all that up to my getting used to the forum. Things are much better now and I don't mind saying that I'd like to buy Duffy a bear someday!

I'm sorry if I offended anyone. ZT

 

[Sceadwian]

You're still on my 'not to piss off' list =) You can buy me a bear too if it makes ya feel better though I'd prefer a beer myself, I'm not sure where I'd put the bear. The wife I'm sure would object, and that would be a sad trip back to the circus. But I digress.

 

[ZTatZAU]

It sounds like there might be a deviation between the schematic diagram drawings and the as-built circuit boards.

It is something of a mystery as to why you are not showing three individual wire leads coming from the large wire coils that are exterior to the rotor housing.... assumed to be L-1 and L2. What are the yellow and white wires ...4 in all .... that appear in the very last of your photographs? ... I can't tell what they are connected to.

It may be that in a certain production era of electronic parts, the Q-13 transistor, an MJ2253, had a different case style.

It might be interesting to access the appropriate leads to the gyro circuit board .... one being the L-2 coil termination that goes to the switch, the other being the Q-13 emitter terminal .... that's the one with the arrow pointed inward ... and see if you could manually get the rotor to rotate a turn or two .... just by touching the negative capacitor terminal wire between these two points.

Hi User_88,
I've always been stumped by the 2 wire 3 wire thing and by L-1 and L-2 and what they really represented in terms of the gyro coil. I know I've got two different versions of the little circuit board so there must be some deviations.

I think you're also right about different case styles being made back in the
60's and I'll definitely print out and try your suggestion above and let you know what happens. ZT

 

[ZTatZAU]

Skeadwian...
Now don't get me started!

 

[duffy]

Do the 2N3055's lead out to some connector on the back of that panel?

Trace down the other circuit. Follow those two sets of twisted white and yellow wires and see if they lead to that trimpot.

 

[user_88]

... grayed out coils....with yellow and white wires

It looks like you are right about the two 'grayed out coils' being a part of the output signal circuit. The small metal crossbar between the two small coils should be slightly movable, relative to the coils.

When the airframe turned or rotated ... as in banking left or right ....
a resultant gyroscopic force would deflect the two small springs which are attached to the rotor assembly tab .. and the metal crossbar end pieces would move proportionally within the two small coils.

The resulting output signal would be amplified and sent to an actuator motor...
maybe to move some sort of compensating airfoil surface used in a turn.

The 10k R-3 potentiometer would used to zero the signal.

 

[ZTatZAU]

Duffy said...Look, the biggest drivers on there are those 2N3055's. What's the biggest load? Appears to be spinning the gyro. Show me something on there that will pull more juice than that.

Assuming it's that big coil around the middle of the thing, then the 2N3055's are suppose to be driving that, and this explains why you don't have that third wire.

Trace down the other circuit. Follow those two sets of twisted white and yellow wires and see if they lead to that trimpot.

Hi Duff, Hi 88, Thanks again for your replies!

I am much more attuned to the mechanical than the electrical (which, I must confess, I've always seen as bordering on the magical) but I would think the biggest load in the system is, by far, the servo motor which can exert a force of 45 Lbs on the mechanical drive cable.

Oh shoot! 88- I forget to answer your question about the twisted white/yellow pairs so I'm glad Duffy asked again. These pairs carry the output signals from the gyro (go left/go right) depending on the tilt of the gyro. The resulting rotation of the gyro's gimble (iron bar?) which changes the air gap at the two little side by side coils that were "grayed out" in the original schematic. I believe those output signals (adjusted for proper centering at the 10K pot) go into the rest of the circuit and (here's the magic part for me) find their way to the 2N3055's, where they get processed and amplified (or whatever they do) and then out to the servo motor.

I did pull a transistor (marked 2N5192) that I think is Q-13 (marked MJ2253 on the schematic) from the spare little board and it tested bad as a PNP. I compared the data sheets and these two transistors are somewhat similar. The MJ2253 data sheet was labeled as abbreviated (and I couldn't find the complete data sheet) but the numbers included in both sheets looked like this.
MJ2253 PNP Vceo = 60V, Ic = 3A, Hfe = Min 20 - Max 100, Fr = 3 Mhz
2N5192 PNP Vceo = Min 60V - Max 80V, Ic = 4A Hfe = Min 20 - Max 80, Fr = 2Mhz
I don't have any feel for how similar is similar enough but are these two devices pretty close electronically?

The bad news is I gotta' get going on my income tax. So I will be temporarily distracted from this project.

The good news is I heard back from a friend, who has a friend, who knows an old timer who may be able to dig up an parts listing for the device. I have my fingers crossed for luck on that. As 88 suggested, that would help enormously!
TTYAL, If all goes well, I'll be back on this at 12:01 April 16th! ZT

 

[ZTatZAU]

It looks like you are right about the two 'grayed out coils' being a part of the output signal circuit. The small metal crossbar between the two small coils should be slightly movable, relative to the coils.

When the airframe turned or rotated ... as in banking left or right ....
a resultant gyroscopic force would deflect the two small springs which are attached to the rotor assembly tab .. and the metal crossbar end pieces would move proportionally within the two small coils.

The resulting output signal would be amplified and sent to an actuator motor...
maybe to move some sort of compensating airfoil surface used in a turn.

The 10k R-3 potentiometer would used to zero the signal.

Right on 88! I was writing and posting my version of the same thing when you posted.
TTYL, ZT

 

[duffy]

See if I got these diodes right, and if those components with the "?" are caps or not.

If that little board is driving that coil, it looks like it's an NPN collector drive, and I don't see anything in the circuit to reverse the polarity.

 

[user_88]

2n5192 ....

The 2N5192 is an NPN transistor .... so it would not test the same as an MJ2253 PNP transistor.

Duffy is right about the LED and phototransistor .....

But what about the Q-13 transistor?

Where is it mounted? .... It ought to be there if there is any similarity to the original schematic.

 

[duffy]

Maybe the circuit board that you have ... and have a picture of ... is just not the same thing as the original schematic that you first posted.

ABSOLUTELY it is not the same.

I am curious about the metal can transistor in the center of the small board.
It would be interesting to confirm if is PNP or NPN .... it has hole cut in the board for its top ....

What, the phototransistor? It's NPN - look at the emitter tab and the voltage connection.

There's an LED and a phototransistor on there to detect the black part of the flywheel, apparently. OP said another style used an incandescent lamp, and the schematic was from one that looked like it used a switch.

 

[user_88]

... right .

 

[ZTatZAU]

Pay dirt!

My taxes are on hold! At least until I get this posted... My friend's friend's friend really came through in spades and provided a lot of good info!

The little board does indeed drive the gyro and there were at least four versions of the Gyro CB. Each was declared obsolete and unavailable when the new version was released. Because the rest of the circuit remained unchanged, a new schematic was never published. When a Gyro CB failed it was simply replaced with the current version of the board. Nobody ever repaired them (it was usually the little light bulb) ; the boards were simply replaced. This was much better for cash flow unless you were the guy paying the bill.)

The board I'm using (the green one) looks to be version 3. The older gray colored board is version 2. The little schematic in my original post... (Hats off to Larry!!! And a great job on the schematic) ... is version 1 which did use a switch.

We can forget the L-1 / L-2 problem and the 2 wire / 3 wire coil dilemma. I now have in hand (and attached to this post), a parts list and component layout illustration... (hats off to 88! A great suggestion that really paid off) ... which includes a schematic of version 4! Version 4 looks, to my untrained eye, to be almost identical to version 3; save for where the power leads connect to the board and a slightly different configuration of components. I haven't yet checked the indivdual component count and markings but will do so in short order.

My confidence level and the odds of success have skyrocketed!!! The gyro's still only spinning a half a turn at a time but with this new info and a bit more help I'm sure we'll get this running again. My green's board did originally have a burned out light bulb. So a while back, after applied power to the board, I measured the voltage across the bulb's leads. It was 6V. So bulb in hand I went down to radio shack and got a similarly shaped 6V mini lamp. The parts list (which is almost complete) calls for a 14V - 640 T1 - 1/4" lamp. So my first question is what effect could the 6V vs 14V bulb have on the circuit? Too much or too little light? Too little or too much resistance in the circuit?

Another question, the gyro (coil) that the little green CB came from, had overheated so badly that the interior of the gyro housing had puffed up and expanded to the point of fully encapsulating the rotor and gimble; locking them both in place. Is there a single component failure on the new schematic that would have likely caused this much overheating?

Thank you all again! I feel like I've learned a lot with all your help and I hope you have enjoyed the primer on gyro systems! ZT

 

[duffy]

Another question, the gyro (coil) that the little green CB came from, had overheated so badly that the interior of the gyro housing had puffed up and expanded to the point of fully encapsulating the rotor and gimble; locking them both in place. Is there a single component failure on the new schematic that would have likely caused this much overheating?

The drive transistor. They tend to fail short, and the coil's only intended for intermittant duty.

That new schematic does not match up with that green board.

 

[ZTatZAU]

Hi Guys,

The drive transistor. They tend to fail short, and the coil's only intended for intermittant duty.

That new schematic does not match up with that green board.

What do you mean by drive transistor? Drives the circuit, drives the gyro coil? Is the drive transistor the photo-transistor?

Don't you think the new one is a lot closer than one we had <BG>?
Do you see any pulsing or reversing going in the new schematic? If so can you explain?
Do you see the long gray rectangular adjustable resister on the green board as a speed control?

 

[duffy]

Check my post on the previous page - I have the drive transistor marked "driver". Not the phototransistor, they can handle very little current.
The new schematic is closer, still not the same - count the transistors.
I don't see any reversing going on, but there's a pulse generator that's triggered by that Darlington (Q1 and Q2).

The adjustable resistor controls the width of pulses going to the motor, looks more like a start circuit than a speed control. That's a 10 or 20 turn pot, by the way.

 

[ZTatZAU]

Check my post on the previous page - I have the drive transistor marked "driver". Not the phototransistor, they can handle very little current.
The new schematic is closer, still not the same - count the transistors.
I don't see any reversing going on, but there's a pulse generator that's triggered by that Darlington (Q1 and Q2).

The adjustable resistor controls the width of pulses going to the motor, looks more like a start circuit than a speed control. That's a 10 or 20 turn pot, by the way.

Hi Duff,
I looked at your tracing and labeling on the double board photo. The "driver" you labeled is marked M226 43A68. Close to some of the p/n on the new listing.

I count 6 transistors on the green board and only 5 on the drawing.

How sensitive are the photo transistors? Might the wrong lamp (6V vs. 14V)effect its operation?

Start Circuit? Can you expound on that relative to the new schematic?. I've had the feeling I'm stuck in some sort of start phase. Maybe a few turns back and forth might bring that pot back?

How about C-1, C-2, C-3, and C-4 in the new drawing... Does current ever flow thru them? Intermittent bursts maybe? Or do they just smooth out ripples in whatever they're parallel to?

EDIT: I found a datasheet on the photo transistor MRD 300 and will spend some time trying how to interpret it.

EDIT And can you explain the Darlington Q-1, Q-2 circuit or branch?

AND what would be the "driver" in the new schematic? Q-5?

TTYL, ZT

 

[user_88]

When Q5 turns off, sharply, the flow of current through L1 and Q5 is interrupted and you get a sort of 'water hammer' effect, except with electric current rather than water.

The resulting voltage pulse travels through R10, CR2, R5, and R7 to turn on Q1, and reverse the current flow, which goes through Q1. .... Can you get the value of R8?
...either from the board or page 2 of the parts list. .... Also, it looks like some of the reverse current pulse goes through CR1 and R3 .... It's not really an efficient design, but apparently they got it to work.

You probably need to adjust the R7 pot. so that Q1 turns on just as Q5 turns off.

It ought to work if you can adjust R7 ... When you turn the R7 screw, take note of how many turns or quarter turns one way, and then the other that you adjust ... so you can go back to the original position if necessary.

Duffy says that Q1 and Q2 are a Darlington pair, but I'm not so sure. If Q1 turns on, then Q2 would tend to turn off. ... And Q2 current goes to a different place than Q1 current.

I would replace the 6V bulb with a 12V DC version.... probably last longer.

Also, maybe replace Q5, the power transistor. If there is evidence of heat damage, it may be defective. ... I would check it with a transistor testor ....They used to be easy to find ... not too expensive.

I don't see any speed control ... just that Q1 threshold using R7.

The new circuit and layout are not exactly the same .... but maybe close enough.

 

[ZTatZAU]

See if I got these diodes right, and if those components with the "?" are caps or not.

If that little board is driving that coil, it looks like it's an NPN collector drive, and I don't see anything in the circuit to reverse the polarity.

I can answer some of this now... but what do you mean "see if I got those diodes right? Do you mean properly identified as opposed to being misidentified as resistors? Polarity (direction)?

Your Question Marks:
? Bottom left... Transistor: marked M224 48S48, same as the one just above it; another 48S48. The top transistor in this row of three is marked: M224 48S64. The 2 transistors at center and top right are marked: M224 48S69 and again the transistor you marked "driver" is marked: M226 43A68.

Many of these cross or close to the new parts list. I'm thinking the 4 digit markings are p/n and not industry standard spec numbers. The M224 and M226 might be case styles? Is this correct?

? Center Right... Unknown: marked 1u with a big K below that. It could be a 1uF cap?

? Upper Left... Unknown marked: T318. The red cap to the right is marked 1mfd 25V monolythic.

Coil connects? Correct as labeled
Power connects? Correct as labeled
Does this mean your red and black tracings on the bottom of the board should be reversed for red power/black ground?

Test? Probably. Nothing connected there and there is a test connect marked on the new schematic.

Thanks again, ZT

 

[ZTatZAU]

When Q5 turns off, sharply, the flow of current through L1 and Q5 is interrupted and you get a sort of 'water hammer' effect, except with electric current rather than water.

The resulting voltage pulse travels through R10, CR2, R5, and R7 to turn on Q1, and reverse the current flow, which goes through Q1. .... Can you get the value of R8?
...either from the board or page 2 of the parts list. .... Also, it looks like some of the reverse current pulse goes through CR1 and R3 .... It's not really an efficient design, but apparently they got it to work.

You probably need to adjust the R7 pot. so that Q1 turns on just as Q5 turns off.

It ought to work if you can adjust R7 ... When you turn the R7 screw, take note of how many turns or quarter turns one way, and then the other that you adjust ... so you can go back to the original position if necessary.

Duffy says that Q1 and Q2 are a Darlington pair, but I'm not so sure. If Q1 turns on, then Q2 would tend to turn off. ... And Q2 current goes to a different place than Q1 current.

I would replace the 6V bulb with a 12V DC version.... probably last longer.

Also, maybe replace Q5, the power transistor. If there is evidence of heat damage, it may be defective. ... I would check it with a transistor testor ....They used to be easy to find ... not too expensive.

I don't see any speed control ... just that Q1 threshold using R7.

The new circuit and layout are not exactly the same .... but maybe close enough.

Thanks alot 88!
I'm still crunching numbers to see how much of my own money I get to keep this year but will print out your explanation and suggestions and head back to the shop ASAP. ZT