After four years of intensive service and repair of SLRs from the 1980s, I'd like to summarize my experiences with the Canon T90.
The T90 was released in 1986 and is considered arguably the most powerful manual focus 35mm camera ever produced.
Canon no longer offers service and repairs; in my experience, repair shops usually reject the T90 because it's considered too complicated. DIY remains an option, and the good news is that most work on the T90 can be performed by yourself. Excellent technical literature available today provides guidance.
Requirements
Performing service and repairs requires a minimum level of repair experience as well as basic knowledge of precision mechanics and electronics. You can acquire the necessary knowledge and skills on your own; excellent specialist literature is available. Courses in analog and digital electronics can support this. Important skills include interest, a willingness to learn, patience, perseverance, and resilience, and, of course, a steady hand. Knowledge and skills in soldering are important for all electronic SLRs.
No shortcuts
I'd like to emphasize that there are no shortcuts to service and repair, as is often the case, especially in videos on the web. The T90 almost always requires more or less thorough disassembly in order to clean, lubricate/oil, and adjust it. This also applies to troubleshooting. Professional step-by-step instructions are available for this purpose.
Without these instructions, I consider any attempts at service and repair pointless, as the T90 must be disassembled in a specific sequence. This involves unscrewing parts and removing solder joints. It's not immediately obvious how to proceed, as the T90 is densely packed with flexible printed circuit boards (FPCs), some of which overlap.
A basic set of tools, equipment and materials is required to carry out the work. A digital multimeter is required for electronic measurements.
Practice
Before you start working on the T90 you're repairing, you should practice all the procedures on a decommissioned T90. This will help you learn how the camera is constructed and gain valuable experience. Mistakes don't matter; you'll always end up with valuable spare parts.
Instructions avaliable
The SPT Journal, March - April 1990, describes the disassembly of the Canon T90 down to the shutter step by step. Technical explanations and information on adjustments are also included. The author is Master Larry Lyells, who, among other things, served as an instructor at the renowned National Camera Repair School and is considered a leading specialist author on photographic technology and repair. We owe him numerous specialist articles that still make repairing older cameras possible today.
Explanations of the electronic circuit of the T90 and systematic troubleshooting are provided by the Canon T90 C & C Associates Troubleshooting Guide.
The Canon T90 Service manual supplements with detailed information on construction, parts and adjustment.
CLA and fixing known malfunctions
Service refers to the well-known CLA (clean lube adjust), which includes cleaning the outside and inside, lubricating/oiling, and adjusting a camera.
For thorough external cleaning, the covers are removed and cleaned with cleaning foam.
For internal cleaning, the mirror box must be removed. This gives access to the mirror box mechanism as well as allowing the shutter to be disassembled and cleaned, which, in my experience, is necessary on almost every T90. The reason for this is a plastic damper in the shutter that, over the decades, rots into a sticky black mass that clogs the shutter blades (sticky shutter). The remains of this damper must be removed, the shutter cleaned, and reassembled. An improvised replacement can be used, but I'm foregoing this and am currently conducting a long-term test with a serviced T90. Cleaning the shutter from the outside as a shortcut does not solve the problem, as most of the damper cannot be reached this way.
The four solenoids of the T90 also need to be cleaned on a CLA. Two of them (for the aperture and mirror release) are located on the mirror housing, the other two on the shutter. If they are dirty, their function is impaired or even nonexistent, as the contact surfaces no longer separate properly or even at all. I clean the contact surfaces with benzine.
On the subject of lubrication and oiling, I refer you to Thomas Tomosy, who, in his first book, "Camera Maintenance and Repair," provides, among other things, a table listing lubricants and their applications. I follow the principle "less is more," and oil, in particular, should be applied sparingly, as it tends to spread. Old grease must be removed first. I also use benzine for this. Information on cleaning mechanical components can also be found in Tomosy's book.
Adjustments affect both the shutter and the electronics. The factory settings should only be changed if you know exactly what they do. Information on this can be found in the SPT Journal. A camera tester is required to adjust the shutter. See the links below.
With the T90, settings are made for the first time using a dial near the shutter release. The contacts on this dial can become dirty, and one or more clicks won't change the settings. The solution is to remove the contacts and clean them with electronic cleaner.
The T90 is notorious for the so-called EEE/HELP error. In this case, the camera displays EEE on the top screen and HELP in the viewfinder. The shutter will then no longer fire. This is often caused by dirt on the two shutter solenoids and/or the sticky shutter, which can be cleaned as described above.
This also applies to an error in which the camera does not fire and an arrow flashes in the top LCD, and a faint ticking can be heard. In this case, the mirror release solenoid is usually dirty and needs to be cleaned. If there are problems with the automatic aperture setting, the first suspect is a dirty aperture magnet.
While reassembling several T90s, I've found that opening the front flex connector (which connects three FPCs by applying pressure) can render the camera inoperable. This is caused by a lack of contact via a conductive rubber strip. I've therefore developed a method that keeps the front flex connector closed. This is important when removing the mirror box.
A word of cautionPlease keep in mind that you’ll be using highly flammable solvents for service work, and their fumes are harmful to your health. Soldering also produces fumes that should not be inhaled. Dangerous high voltages can be present when handling electronics, especially in conjunction with electronic flash units and mains. Therefore, familiarize yourself with the safety regulations beforehand and ensure your safety. Depending on the activity, protective gear may be advisable.
All information provided without guarantee and use at your own risk.
Further information on service and repair can be found here:
Canon T90: Final summary on DIY service and repair
Canon T90: No automatic film feed, problem solved by systematic troubleshooting
Canon T90: Aperture function restored by replacing the aperture control (AE unit)
Canon T90: Aperture issue resolved, shutter disassembled and cleaned
Canon T90: Solution found for the stubborn front flex connector, service and repairs on the T90 are no longer a gamble
Canon T90: release magnet, EEE/HELP/bc, mirror shock absorbers and cover, front flex connector acting crazy/alternative?, victory, shutter magnets
Canon T90: Service and repair using practical examples
Canon T90: EEE error resolved - hint for disassembling/assembling; sticky second shutter curtain; setting the 1/4000 second
Canon T90: systematic troubleshooting, DC/DC converter replaced, one LED digit missing, sticky shutter, EEE again, summary
Canon T90: Address unresolved problems; broken plastic parts in Copal S shutter, epoxy, EEE/HELP/bc errors, troubleshooting partially successful
Canon T90: The infamous HELP/EEE error fixed through guided and systematic troubleshooting
Canon T90 and T70: Rescuing victims of leaked battery electrolyte
Canon T90: Defective display replaced
Canon T90: Power supply restored
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