Canon T90: Address unresolved problems; broken plastic parts in Copal S shutter, epoxy, EEE/HELP/bc errors, troubleshooting partially successful

[Andreas Thaler]

I see, yes. Perhaps it's possible to glue it in situ?

Spring forces act on the spot. And that's where my fine motor skills end

 

[Andreas Thaler]

The epoxy is now solid.

When tightening, you can see that the spring moves slightly under the epoxy droplets on the left screw.

This is perhaps a good thing; in any case, the curtain travel times have remained stable and have even improved

I'm now installing the shutter into the T90 and am curious to see how the shutter speeds will work. The T90 controls these electronically. The camera must be mounted for this.

 

[Andreas Thaler]

EEE and HELP

The tests coupling the shutter and mirror to the motor worked after inserting the mirror box. This passed the most critical part.

During the first test of the T90 after complete assembly, EEE and HELP appeared. And immediately after switching it on.

I went through the troubleshooting instructions, removed a double diode to test it, re-soldered the circuit board connections, checked the connectors, as well as the magnets, which worked.

I then replaced the DC/DC converter three more times because a reference voltage was not appearing there.

Voltage measurements on IC3, the main CPU under the LCD, did not match the specified values. So I finally replaced IC3, but that didn't work properly with the soldering of the 60 pins. I'm not equipped for this fine work. And I was already outside the service instructions, which don't recommend it, but recommend replacing the entire mainboard

This puts this T90 in the spare parts box.

I'm removing the shutter, which I had treated with epoxy. It's going into the next candidate to test it


What could be the cause of the error?

What surprised me was that 15 volts weren't measured on the DC/DC converter; the voltage wasn't reaching the terminal. And that was the case with three DC/DC boards. So that rules out a fault.

But voltages were measured on the board. So, it wasn't a short circuit.

The only explanation I can think of is that IC3 was actually faulty. The voltages that weren't appearing at certain pins support this. And the technical documentation also says that.

Anyway, there's more to come.

Stay tuned!

 

[Andreas Thaler]

Replacing the electronics to fix the EEE/HELP error

After a long sleep and a hearty breakfast, I took the T90 out of the spare parts box and continued working

Since I couldn't locate the fault, I replaced the entire mainboard, providing most of the circuitry and connected to the mirror box which I also replaced. A spare parts T90 was looted.

But that didn't solve the problem either. As soon as the camera is turned on, the winding motor still moves briefly and EEE/HELP appears.

So today I removed the motor flex board from another spare T90 and will install it in my patient tomorrow.

Then most of the electronics will be replaced, and hopefully, the error won't have too many possibilities anymore.


Cleaning the release magnet

Before assembly, there is a test routine for the coupling of the motor, shutter, and mirror box.

During this process, the release magnet failed.

This was quickly resolved by removing the magnet and cleaning its contact surfaces with benzine.

You can see the contamination in the photos.


Simple tool to trigger the shutter magnets

To test the electronic triggering of the two shutter magnets, I built a double contact that is fixed with shrink tubing.

It is connected to the laboratory power supply, which is set to two volts.

This allows the magnets to be triggered directly via the contacts on the shutter board.


Curtains travel times hold

The shutter, which I adjusted yesterday and stabilized with epoxy, is doing well.

The curtains travel times are holding up.

Stay tuned!


+++

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

 

[Andreas Thaler]

Check and repair of soldering connections

Before replacing the motor flex board, I checked some solder joints that had been damaged during desoldering. Perhaps that was the cause of the problem.

Damage to the contacts that could lead to wiring problems.

Continuity test contacts to DX contacts in the film chamber for automatic ASA detection.

Bridging a defective connection with tinned copper wire. Flux shines at the solder joints and on the board.


A test showed that this was not the cause of the problem.


Removal of the motor flex board

Upper part of the board with red and black motor connectors.

Power supply for the motor flex board on the release side at the front.

The lower part of the motor flex board.

Removal completed.

Area under the board.


Installing the replacement board

Everything in reverse order.

The new board is installed and still needs to be connected. There's a lot of soldering to do.

The handle goes back into place.

Switch panel assembly.

Inserting the spring into the cover flap was a game of patience.

The wiring of the trigger unit is threaded through the handle.

 

[Andreas Thaler]

Done


After replacing the motor flex board, the status changed from HELP/EEE to bc

The T90 still didn't work.

Instead, a flashing bc appeared on the LCD.

This is also an error message, which - like HELP/EEE - can have multiple causes.

The C&C Associates Troubleshooting Guide for the T90 includes a multimeter troubleshooting routine, which I followed.

Here, I measure the resistance at a pin on IC3, the main CPU.


Suddenly, success arrived. Problem solved!

Switch 13 on the mirror box was obviously contaminated/blocked.

After pulling the mirror housing out a bit, I was able to clean the switch with electronics cleaner.

And with that, the T90 was suddenly alive again. All its functions were there

Description of SW 13 in the SPT Journal:

SW13. Mirror switch on mirror box,
Fig. 13 (direct connection to SP flex
- connects to IC3 pin 19 through
front flex connector). Normally
closed, connecting pin 19 to ground.
Opens when the mirror is up, telling
IC3 to release the shutter.

Here is the gold-plated switch on a mirror box for spare parts.


On the camera tester

Now I could finally test the shutter, which I had disassembled, cleaned and stabilized with epoxy, on the camera tester.

The curtain travel times (C1 and C2) remained stable.

It's hard to believe that these sensor data add up to 1/4000 of a second.

But it was meant to be. Here I tested the 1/4000 second in TV mode with a lens. The exposure result was correct.

An acceptable result in Program mode too.

Many hours of work paid off. I was able to rescue another T90 from the spare parts bin

 

[Andreas Thaler]

Conclusion

• Systematic troubleshooting following professional instructions proved its worth here, too.
• Without the SPT Journal and the C&C Troubleshooting Guide, such a repair project would not have been feasible. Especially since I'm not aware of any Canon troubleshooting guide for the T90.
• Working on the T90 is fun this way. With the available technical manuals and spare parts from discontinued T90s, there's a realistic chance of troubleshooting.
• It remains unclear why errors occurred on two different motor flex/mainboards with two connected mirror boxes and overall three DC/DC converters. One time, EEE/HELP, and the other, BC. Perhaps a problem repeatedly occurred when coupling the mirror box to the motor and shutter, which was resolved by pulling out the mirror box?
• But ultimately, all that matters is that the camera is up and running again

+++

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

 

[Andreas Thaler]

The joy didn't last long

After a continuous shutter release in high-speed mode, the viewfinder LEDs failed and the camera stopped shooting. Then, bc.

I followed the troubleshooting instructions again, discovered incorrect timing on SW15, fixed it, but no change.

SW15. Charge-pulse switch at
bottom of camera, Fig. 21. As the
charge-cam gear, Fig. 20, turns, its
brush moves along the contacts of
SW15 to provide a pulse signal to
pin 41 of IC5 (green wire, Fig. 29, to
ground).

SPT Journal


There's nothing more I can do. At least it's an interim success.

Currently, it's 1 to 3; maybe I can improve my score next week; there are still candidates waiting I have spare parts again now.