Minolta Auto Winder G: Service and repair

[Andreas Thaler]

Review of Minolta Autowinder G #2

In this example, the motor also runs continuously when you press the shutter button on the camera.

Capacitor #1 (10uF/16 V) has electrolyte on its terminals, so it is leaking.

Capacitor #2 (4.7 uF/25 V) shows slight traces of electrolyte.

The counter contact of switch S 21 is dirty. I clean the contacts with isopropyl alcohol.

After reassembly, the winder behaves the same as before. So the problem is obviously not with the switch.

I start to desolder the two electrolytic capacitors so that I can measure them later.

For desoldering with desoldering braid, I use a powerful cordless soldering iron with a wide tip. With this, and plenty of flux, it is quick and thorough.

The two terminals of capacitor #1 are now free of solder.

The capacitor can now be removed from the circuit board.

Capacitor #2 (4.7 uF/25 V) is harder to reach in the case. Shining a light through the board will reveal where its cathode is connected.

Here are its two soldering points on the board.

Desoldered

When desoldering both electrolytic capacitors, it is important to note that they each share a soldering point on the circuit board with the connection of another component.

The cathode of the capacitor has been desoldered, but is still connected to a resistor terminal. The two can be separated using the soldering tip.

Done

A photo that shows me the correct polarity of the capacitor on the circuit board for a replacement later.

The two old guys are waiting for their measurement.

Using the rubber polishing tip on the Dremel Stylo, I clean the connections for optimal contact with the measuring device.

Capacitor #1

• nominal capacity: 10 uF
• The actual value cannot be measured

This capacitor is defective.

 

[Andreas Thaler]

Capacitor #2

Nominal capacity: 4.7 uF
Actual value: 2.58 uF

This capacitor is also defective.

In an electrolytic capacitor, the cathode is formed by liquid electrolyte. If the capacitor runs out after decades, the surface area of the cathode becomes smaller and the capacitor can therefore only store less charge. That's how I explain it.

---

Conclusion

• This confirms to me that the leaking capacitors are the cause of the problems.
• After the exchange we will see if this assumption is correct.

I will now look at how this could affect the circuit.


+++

All information provided without guarantee and use at your own risk.

 

[Andreas Thaler]

Function of the two electrolytic capacitors in the circuit

The Minolta Autowinder G is controlled via an analog circuit.

All components such as transistors (Tr), resistors or diodes are installed discretely, ie as individual electronic components and not as an integrated circuit.

The camera controls the winder via two voltage ranges.

Electronic circuit Minolta Autowinder G

(Source: Minolta Service Manual for Auto Winder D and G)


Simplified switching sequence

• The winder is started via a contact on the bottom of the camera, several transistors switch the current.
• The two electrolytic capacitors (red rectangles) are connected to the gate of the thyristor (green rectangle).
• Electrolytic condenser C1 discharges via TR2 and the voltage divider made up of resistors R4 and R5. This charges C3 which ignites the thyristor and turns on TR1.
• The emitter current from TR1 flows through the coil of the relay that switches the motor (M).
• Almost 1 ampere of current flows through the circuit when the film is transported.
• By means of a mechanical device, switch S21 cuts off the thyristor, so that no more current flows through TR1 and the relay which switches off the motor.

I conclude that the thyristor, transistor and relay cannot work properly if the two electrolytic capacitors are defective. This impairs switching of the motor.

The transition from perfect function to total failure seems to be seamless.

Both winders worked normally for a while, then malfunctioned and finally one stopped working altogether. This means that the two capacitors continued to function with limitations for a while.

I am curious to see whether replacing the electrolytic capacitors will solve the problems.

 

[Andreas Thaler]

Why two electrolytic capacitors at the gate of the thyristor?

I wonder what function C3 has on the gate of the thyristor, when C1 should actually be enough to trigger it?

C1 obviously charges C3 to ground. As soon as C3 has sufficient voltage, it triggers.

Perhaps this is more stable than if only C1 „spits into the gate“, as the discharge curve is very steep at the beginning and this voltage curve may not be sufficient. C3, on the other hand, is brought up to potential from almost 0 volts.

An attempt at an explanation.


How can the problem with the motor running continuously be explained?

I put this down to the two defective electrolytic capacitors that are no longer working stably. But it is true that once the thyristor has fired, it should not longer care about the two capacitors.

S21 switches the thyristor off mechanically, I cleaned the switch and it works.

The capacitors may not be fully discharging, i.e. they are not releasing their ignition voltage completely. Then the thyristor fires, S21 switches it off and the capacitors ignite the thyristor again.

Very exciting, let's see what the effect of replacing the capacitors will be.

Since similar problems occur with two winders and two others that were working before failed over time a long time ago, it can only be the capacitors. Otherwise, I don't see any components in the circuit that are basically falling apart on their own.

And since I measured both capacitors and found that they are far from the target capacity, I suspect these guys.

---

You could also take a pragmatic approach to troubleshooting and simply replace the electronic components that are defective or suspect. And then see if that was the solution.

But if you look at the circuit as a whole, you learn something new. Even if you have to dig deep into it.

 

[forest bagger]

C1 only buffers the 6 V battery voltage fed by R3 against voltage peaks or voltage drops that occur when the motor is switched on and off.
This voltage is switched to C3 via R4 through Tr2 to activate the film transport, which slowly charges it to the part of the battery voltage that results from the voltage divider R3+R4 / R5. C3 is therefore important for the running time of the film transport.

 

[Andreas Thaler]

C1 only buffers the 6 V battery voltage fed by R3 against voltage peaks or voltage drops that occur when the motor is switched on and off.
This voltage is switched to C3 via R4 through Tr2 to activate the film transport, which slowly charges it to the part of the battery voltage that results from the voltage divider R3+R4 / R5. C3 is therefore important for the running time of the film transport.

This means that Japan has revealed yet another secret!

 

[Andreas Thaler]

C3 is therefore important for the running time of the film transport.

C3 ignits the thyristor, and its job is done.

The thyristor then switches the motor on via the relay and the timing of the transport is determined by S21. This is a switch that is opened by the axis of the transport pinion on the winder after one revolution. This switches the motor off until the next cycle.

A page in the service manual is dedicated to adjusting S21.

However, S4 on the camera, which controls the winder, also plays a role.

I admire the engineering behind it.

The solution is designed and built in such a way that it will work for over 40 years.

The installed (and rotten) electrolytic capacitors can probably only be blamed on Minolta for economic reasons, since they were certainly cheaper at the time than tantalum capacitors, which were supposed to be more durable.

The story behind it can be read here as already mentioned:

Minolta Capacitors

minolta capacitor, x700 capacitor, x570 capacitor, x370 capacitor, x-500 capacitor, x-300 capacitor, xg capacitor, xd capacitor, tantalum capacitor

www.678vintagecameras.ca

 

[Andreas Thaler]

This should essentially explain the circuit.

I'd almost bet that replacing the capacitors will solve the problem.

Reichelt is expected to deliver the new electrolytic capacitors forthcoming Monday

 

[Andreas Thaler]

No problem:

https://www.reichelt.at/at/de/shop/produkt/elko_radial_4_7_f_25_v_rm_1_5_85_c_1000_h_20_-228282

50 4.7 uF/25 V electrolytic capacitors have arrived, so I can use them to get half a century of Autowinder G up and running. Hopefully

It will start soon.

 

[Andreas Thaler]

Repair of Minolta Autowinder G #2 successful

It's time to replace the two electrolytic capacitors. I had already desoldered the defective ones.

Here I thread the electrolytic capacitor with 4 uF/25 V (C3) onto the circuit board.

The cathode, here the rear connection, shares the soldering point with the connection of a resistor, which is also inserted through the drill hole.

The green cable connection is connected to the soldering point at the cathode.

The anode (above) shares the soldering point with the black cable connection.

The connections are soldered into the circuit board.

Wirh the side cutters I remove the excess length of the connections.

This is where the electrolytic capacitor with 10 uF/35 V (C1) comes on board.

Using pliers, I carefully pull its connections through the two holes in the circuit board that share their soldering points with the connections of two resistors.

Done, the electrolytic capacitor can now be carefully bent under the circuit board.

Soldering

Shortening

The two new electrolytic capacitors are in place.

Check the circuit board to see if the soldering points are OK and if there are no pieces of the cut wires left lying around (risk of short circuit).

Assembly without leatherette and test.

The winder runs perfectly in single and series operation. As if it was new

 

[Andreas Thaler]

Conclusion

• Once again, leaking electrolytic capacitors were the culprits.
• Fortunately, replacement is not a problem, the electrolytic capacitors are standard and available new.
• Replacing them requires a bit of work but can be done without complications.
• On this occasion I was also able to learn about the circuit and structure of the Autowinder G. This will help me when repairing the almost identical Autowinder D for the Minolta XD/XD7/XD11.
• It is worth repairing the Minolta Autowinder G. The usual advice to throw away a defective one and buy another used one for little money makes little sense. Basically, all models are affected by the capacitor problem. Unless Minolta also used more durable types.

+++

All information provided without guarantee and use at your own risk.

 

[Andreas Thaler]

And the Minolta Autowinder G #1 also works perfectly again after replacing the two electrolytic capacitors

 

[Andreas Thaler]

I'll close the topic here for now, but will come back with the Minolta Autowinder D and the Minolta Motor Drive MD-1.

 

[forest bagger]

Good work, Andreas!

 

[Andreas Thaler]

Good work, Andreas!

Thank you, Michael

 

[Andreas Thaler]

I have just tested both Autowinder G on the X-500, they work perfectly.

One had problems starting, but these disappeared after re-attaching/checking the battery holder.

This has verified that the defective electrolytic capacitors were the culprit.

I will later look into whether the - older - Autowinder D for the XD also has electrolytic capacitors installed.

 

[xkaes]

Since the MD-1 is in the title, what problems have you run across with the MD-1? I've got TWO, DOA.

 

[Andreas Thaler]

Since the MD-1 is in the title, what problems have you run across with the MD-1? I've got TWO, DOA.

View attachment 385582

Minolta Motor Drive MD-1

The first problem is that there is no complete service manual for the Minolta MD-1

The second problem I caused myself when I wanted to check the installed capacitors and obviously damaged the wiring:

Minolta MD-1 motor drive: Release problems fixed

A Minolta MD-1 motor drive for the Minolta X series, which has misfires on the second release switch laterally and which I treated for the same reason last year. In series operation on an X-500, it stops after a few shots and the red control LED on the back lights up. I suspect contact...

www.photrio.com

 

[xkaes]

OK, but Minolta must have made a service manual. We just need to find one. I'll report back if I have any luck.

What you've reported certainly will help. THANKS.

https://www.scribd.com/document/655497093/Motor-Drive-MD1-Service-Manual-Minolta-en

 

[Andreas Thaler]

OK, but Minolta must have made a service manual. We just need to find one. I'll report back if I have any luck.

What you've reported certainly will help. THANKS.

https://www.scribd.com/document/655497093/Motor-Drive-MD1-Service-Manual-Minolta-en

 

[pentaxpete]

FANTASTIC INFO ! I was given a MINOLTA XG-1 body by a Camera Club member ( Not Working ) and it had the Autowinder G also not working -- now I see i have to take off the Self=Adhesive cover to access screws

 

[Andreas Thaler]

Minolta Service Manual for Auto Winder D and G