T90 woes - fading viewfinder l.c.d. display

[astral]

<p>My T 90 has suddenly developed a problem with the viewfinder spot-meter bar-graph display. Firstly it started flickering, then it became rather dim, and now it has disappeared. Occasionally it re-apperars <em>at full brightness</em> for a few seconds, so it's probably a contacts problem. The l.e.d. display and all other functions are fine.</p>

<p>I have checked various things, and am beginning to suspect that it's the rather notorious panel beneath the palm-wing, or the horrible little connector pads found beneath the meter push-buttons.</p>

<p>However, before I disassemble the camera (<em>this will be the third T90 I have tackled</em> <em>for one problem or another</em> ) does anyone know if there are any other possible causes of this problem?</p>

<p>Thanks, AC</p>

[alan_swartz]

<p>Alan,</p>

<p>Is the LCD not displaying characters, or is it the backlight that has failed? I'll try to have a look at a parts camera tomorrow.</p>

 

[astral]

<p>Alan,</p>

<p>That's tricky, but I think it might be a backlight issue: <em>some</em> of the active (i.e. changing) characters/arrows started <em>flickering</em>, then <em>all</em> of them became <em>dim</em>, then there was nothing as the backlight failed completely. When the display returns, the backlight comes on first, then some characters 'light up' before others.<br>

I have a parts camera too, but it won't power-up.</p>

<p>Thanks, AC</p>

[alan_swartz]

<p>Whether the LCD is illuminated with either external light via the window to the left of the prism hump, or by the internal lamp, it seems it ought to all display at once. If characters are becoming visible in stages, I'd initially say the LCD has a bad connection and all segments are not getting their drive current reliably.</p>

<p>The LCD assembly mounts with screws and some silicone light seal in a stamped metal saddle that is part of the prism-to-mirror box mount (careful--there seem to be oval brass shims under the prism mount screws). The LCD is driven directly off of the flex circuit a matter of millimeters from the nearest IC. It looks like one of those elastomeric compression connectors must be enclosed in the assembly, but it is certainly well executed and robust. There is one screw that does the compression, it appears. You have to remove the LCD piece to get to it.</p>

<p>The lamp is a custom piece, a long rectangular assembly of white plastic, cemented or welded to the LCD assembly right next to the light pipe that reaches up to the top window. It looks something like a fluorescent fixture for a flea circus. It has two soldered pigtails that connect to a different layer of the circuit flex.</p>

<p>Since you have both incomplete data displayed and an intermittent lamp, and they definitely go different directions electrically, I have to wonder if the problem is remotely located, perhaps oxidized contacts in a switch, or a compression connector elsewhere that is intermittent, fouling up both the command to turn on the light as well as the data for the LCD. </p>

<p>That wasn't much help!</p>

<p> </p>

[astral]

<p>Alan, many thanks for the most helpful information. You say:</p>

<p><em>"I have to wonder if the problem is remotely located, perhaps oxidized contacts in a switch, or a compression connector elsewhere that is intermittent, fouling up both the command to turn on the light as well as the data for the LCD".</em></p>

<p>I am coming to this conclusion also; and logically this is the simplest first-level solution - check the push buttons. The give-away clue may be the way the display started going wrong initially - the read-out just lit up sluggishly suggesting, a high resistance rather than a 'broken' or intermittent contact .... but electricity is funny stuff.</p>

<p>The camera still has film loaded so I'll defer doing this job until a rainy day, when I can also practice on the scrap T90 first. Many thanks for the input: I'll post back any outcomes once I've taken the plunge. Regards, AC </p>

<p> </p>

[douglas_vitello]

<p>Off subject but just a personal comment.It looks like as this system ages the last man standing is going to be the "F" Series.The lenses last forever but time is taking out more and more of the electronic wonders we love.Probably a good window into the future regarding EOS too.I doubt I'll ever part ways with my F1n even though I much prefer shooting with the F1N.</p>

[astral]

<p>Douglas - my feelings too. I have a very great liking for Canon FD lenses and my FTb/FTBn and (non-AE) F1N. But I am beginning to feel that my two T90's days are now numbered - I am not prepared to spend 'big' money on them. Paradoxically, my A1 has just been serviced .... it now works perfectly, but I really do hate it. The only camera I really do 'love and trust' any longer is the F1N. Mebbe I should sell everything else and buy a back-up one . . . . . . .</p>

[User_4136860]

<p>I have all these cameras Alan, and I feel the same way about them, I just had them all seviced, and feel that that they all will still be working in another thirty years.</p>

[User_4136860]

<p>The T90 has an internal lithium battery that powers the display that was supposed to be replaced every five years according to Canon at the time that wasn't user replaceable that powers the LCD display,(If this cell fails ISO 100 flashes on the display), and It's 23 years since the cameras were made, so It's surprising so many of them still work.</p>

[User_4136860]

<p>Please ignore my last post, I got the wrong end off the stick it was the <em>viewfinder display</em> the OP was writing about, Doh, I tried to delete it but couldn't</p>