Canon T90: Defective display replaced

[Andreas Thaler]

Checking my little T90 family, I saw that one family member was having problems with her display on the top of the case.

When the camera was switched on, but also every time any button was pushed or the selector wheel was turned the display showed signs and symbols that did not match the respective mode:

After two seconds the spook disappeared,

then returned as soon any setting was done.

Settings were also not displayed, eg from changing from Av to Tv or from selective metering to spot.

This meant that the otherwise very nice T90 could no longer be used.

That would have hit me hard.


So I thought about what could be the cause of the error.

The LCD itself did not appear to be defective, as only regular characters and symbols were displayed, but they did not match the respective operating mode or disappeared by themselves.

So the problem had to be either a broken IC driving the display or a bad contact on the board.

In the absence of a circuit diagram and the lack of options to test or replace ICs (soldering work for this is beyond my technical and practical possibilities), I used my magnifying glasses to look for any defective solder joints or cables. At least on the top of the circuit board, which became accessible after removing the upper part of the housing and the front panel.

But there was nothing conspicuous to discover here, so far everything is flawless.

„That's it with this T90“, I thought to myself. But at least a bit practiced disassembling.

Then I remembered the the parts of the T90 that I had recently dissected for study purposes.


I could try changing the display

I had a replacement.

Maybe that fixes the issue.

And if - which was likely - not, then I could at least practice desoldering and soldering on the flexible circuit board. Not a popular task, as everything is small and built-in - damage can quickly be caused by too much heat.

I didn't think twice, got the replacement display and took a look at how it's set up.

The display forms an unit with a circuit board underneath. The connector on the flexible board is soldered to this board:

I separated both parts.

It took me a while to make it.

Desoldering pump and desoldering braid were used.

Then the flexible circuit board could be pulled off whereby the contacts remained intact so far:

The T90 already open:

Unscrew and lift the display.

Then I desoldered the red and black cable, the power supply according to the colors:

In order to be able to separate the two circuit boards by desoldering, I folded the display out of the camera and fixed it with soldering tweezers and adhesive strips.

That meant stress for the fine conductor tracks, so I checked in between with the battery holder inserted and whether the connection was still intact:

Now it was time to desolder and separate the circuit boards, which finally worked:

The - presumably - defective display:

And the replacement display, already soldered in.

Of course, I couldn't do the soldering as nicely as the fitters at Canon, but it worked:

Now restore the power supply with the red and black cable:

A test...

... and I didn't believe it myself:


The display showed correctly again!

The assembly then went quickly and I tested all the settings.

Indeed, the T90 had come back.

Everything as usual on the display, including the associated camera functions:

 

[Andreas Thaler]

A crowded table again:

And the star of the day

 

[ic-racer]

Just like the nice viewfinder display repacement you showed us, I wonder about the LCD display you removed. Could it have been corroded or bad solder joints?
Anyway, another very nice repair!

 

[Andreas Thaler]

Just like the nice viewfinder display repacement you showed us, I wonder about the LCD display you removed. Could it have been corroded solder joints?
Anyway, another very nice repair!

Thanks!

I will investigate the issue with the faulty display soon

 

[ic-racer]

I'm a Canon idiot, so I had to look up the T90 to compare it to the AF Nikons I have collected. As I have not experienced any of the issues you see with the T90 with my Nikons. Turns out, the T90 is of the same vintage as Nikon F3AF, F-501(N2020), F-301(N2000). So that answers the question as all 9 of my Nikons are at the far right of this chart; the latest models: F6, F100, N80, N75 and N55.

Is this your understanding? The T90 was a contemporary of the F3 Autofocus?

Back in the day I was using Rollei 35mm and ignored any of the fancy autofocus cameras until the 2000s. So I don't really recall what-was-what back then in the Autofocus market.

 

[Andreas Thaler]

Turns out, the T90 is of the same vintage as Nikon F3AF, F-Is this your understanding? The T90 was a contemporary of the F3 Autofocus?

The Nikon F3AF was released in 1983 as far as I know the Canon T90 in 1986.

I think you cannot compare them.

The T90 was way ahead of its time. Even today it is a capable machine challenging to take advantange of all features offered.

The F3 is a workhorse reduced to the absolutely necessary.

Both are impressing milestones worth the effort to keep them

 

[ic-racer]

T90; The Tank!

 

[Andreas Thaler]

T90; The Tank!

Indeed!

 

[Andreas Thaler]

I accept my de(soldering) work as the camera works but I am not happy with that.

At all a lot of stress for pads and contacts.

I wonder what it needs to do the work gentler. Equipment for de(soldering) SMD parts?

 

[Andreas Thaler]

Hot air can not be dosed like heat with a soldering tip. With that I would probably melt down the flexible circuit board and the plastic carrier.

I think the soldering tip is right here.

The new solder points also look a bit bumpy because the contacts underneath have already been taken with the unsoldering. But managed to connect everything.

Unsoldering the flex circuit board from the circuit board under the display was a sometimes tedious affair.

The solder above the contacts could be sucked off with the desoldering braid. But there was also solder underneath. Maybe I should have lifted off pad by pad, but it worked with careful peeling.

Soldering in this environment is not really fun ;-)

 

[Andreas Thaler]

Canon T90: defective display examined

Today I took a detailed look at the defective display that I had exchanged for a working one in the T90.

Possibly a clue for the indication error could have been found.

The fact that the fault had to be in the display unit and not in another area of the camera electronics was shown by the successful replacement of the unit before.

The components of the unit attached with clips and elastic glue/rubber.

The LCD is placed over a circuit board with IC.

The area around the IC looks healthy. When replacing the display unit, I detached the connection to the flexible printed circuit board from the underside, hence the traces of desoldering.

The display that is connected to the circuit board via two conductive rubber strips.


Here, too, I can't find anything conspicuous under the magnifying glass.


Conclusion

Two components can be considered for the malfunction:

1. the IC
2. the conductive rubber strips

The IC could only be exchanged for one from an abandoned T90. Very tricky soldering work as there are many small pins.

The conductive rubber strips could be cleaned with isopropyl alcohol.

Afterwards assembly of the unit, installation in the T90 and test.

I think it's easier to swap out the entire unit.

 

[Andreas Thaler]

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Trim probe tips

On this occasion, I used the Dremel Stylo to sharpen the already softened and bent tips of my probes.

The probes were very helpful in separating the components of the display unit.

A good fixation in the vice and that the whetstone rotates away from the tip of the probe is essential. Otherwise the whetstone will bounce off the tip.

Safety goggles are mandatory for such activities.