I've spent several weeks working intensively on the Canon T90 and have written a few articles here.
Sufficient to summarize what I have learned so far.
Findings, observations, insights
- The main cause of the common problems are dirty magnets and contacts. Cleaning fixes this.
- The EEE/HELP error codes usually occur when the trigger sequence is interrupted and the shutter does not fire. This can be caused by dirty shutter magnets or sticky shutter blades. But contact problems with switches or with the connection of circuit boards (front flex connector) interrupting the trigger sequence can also be a cause.
- If the camera does not release, a fine click is heard and an arrow flashes in the main LCD, the release magnet is most likely dirty.
- Problems with the release magnet can also cause the T90 to switch from HIGH to LOW motor mode. This can also occur due to overloading caused by a stiff aperture mechanism on the lens and is an intentional automatic measure.
- Likewise, problems with the aperture can be traced back to a dirty aperture magnet or dirty/worn out contacts in the aperture control (flush plate, AVO).
- The dropouts on the command wheel are also caused by contact problems.
- In contrast, errors caused by defective electronic components seem to be rare. I once had an obviously defective main LCD control IC, a defective double diode and an overloaded electronic component on the DC/DC converter. I was able to replace with parts from spare T90s.
- The well-known sticky shutter (caused by a sticky damper in the shutter for both curtains) is now apparently occurring in most T90s. The rotten damper can be removed, and operation without a replacement is possible. Long-term effects on the shutter during intensive use remain to be observed.
- The plastic worm screws in the T90's shutter can break, presumably due to prolonged spring force. Adjustment is then no longer possible. As long as the factory settings are not changed, this is not a problem. The screws can be permanently secured with adhesive or replaced (spare T90s).
- Compared to other SLRs with vertical focal plane shutters, the T90's shutter is easy to disassemble and presents no particular challenges (e.g., springs that behave treacherously or screws getting stuck). Cleaning is also straightforward, and all components are sturdy and can withstand considerable stress when handled.
- When reassembling the T90, contact problems can occur in the front flex connector. One solution is to leave the connector closed during disassembly. Most common service and repair work can be performed this way.
- Leaking battery electrolyte can disrupt the battery contacts in the battery case and spread through the cables to the DC/DC converter board. Cleaning or replacing the cables is the solution.
- The T90 is designed to be easy to service (compared to other SLRs of the time); disassembly mainly involves removing solder joints. This makes the T90 ideal for DIY, especially since it doesn't require any special Canon equipment or software for service.
- On all the T90s I opened, the screws holding the mirror box and lens mount were loose. They should/can be easily retightened.
- Fungus can build up on (from the outside) inaccessible side of the eyepiece; this should be checked when disassembling.
- The built-in 3 volt lithium backup battery was in very good condition in all opened T90s and therefore did not need to be replaced.
- Spare parts can be obtained from abandoned T90s. Defective T90s are currently offered at relatively low prices.
- The technical documentation for service/repair available is excellent. The SPT Journal, C & C Guide, and Canon Service Manual allow problems and service work to be addressed systematically and specifically.
Comment on the known fixes for problems
Hit the T90 hard to loosen stuck magnets
This only helps temporarily at best, as it doesn't address the underlying cause - contamination of the contact surfaces between the magnet and its armature.
Beside that no SLR should be treated roughly.
The sustainable solution is to remove and clean the magnets.
„Remagnetizing“ the release magnet on the mirror box
For this purpose, a magnetized screwdriver is recommended, which is held against the magnet while the camera is triggered.
This is a hybrid magnet that permanently attracts its armature and releases it when current flows through its coils. Therefore, a magnetized screwdriver can at best briefly amplify the resulting counter-magnetic field, helping the armature to release. However, this does not remagnetize the magnet.
Cleaning the magnet is also the permanent solution here.
Keeping the T90 fit by regularly firing and avoid the damper in the shutter becoming sticky
Regularly triggering the T90 can help prevent dirty magnets from getting stuck. However, for a long-lasting solution, the root cause - contamination - must be removed.
Regular use has no effect on damper rottening. Rather, it accelerates the slats' contamination.
What causes the common problem of contamination of the four magnets in the T90?
Gus Lazzari, a well-known US camera repairer with decades of experience, said:
Therefore
Don't give up on your broken T90.
It has its problems, but the chances of DIY solving them are good!
Service and repair on the Canon T90:
Search results for query: T90
www.photrio.com
Technical documents available online:
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All information provided without guarantee and use at your own risk.
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