Canon T90 issue........not the usual one though !

Firestarter · Sep 14, 2018

Some weird stuff happening with a Canon T90 I recently picked up. I was aware of the shutter issues these cameras suffer but wanted to purchase one anyway.

The shutter is working perfectly, in fact most things are apart from two things.

1, The DX codes always read at a quarter of film ASA so for example 100ASA loads as 25 ASA, 200 ASA loads as 50 ASA ?

2, A weird problem. At times when pressing the metering mode button to change for example from average to spot the camera forwards the film as if you have just loaded it ?

Anyone have issues like this before with a T90 or have any idea what the hell this mad electronic box is thinking ?

Firestarter · Sep 14, 2018

Think I may be getting somewhere with the meter button. it doesn't seem to be the meter button causing the problem after all. It seems that putting any kind of pressure or twisting motion on the camera top plate in the vicinity of the meter button makes the camera think I have just loaded a film. So looks like it may be a switch or similar for the film door that is causing the problem...must look further !

abruzzi · Sep 14, 2018

Firestarter said:
1, The DX codes always read at a quarter of film ASA so for example 100ASA loads as 25 ASA, 200 ASA loads as 50 ASA ?

Have you tried other speeds?

I looked at the actual codes (speed is just the first line): https://en.wikipedia.org/wiki/DX_encoding

100 is: XOXOX
25 is: XXXOX

200 is OOXOX
50 is: OXXOX

The difference in both cases is the second block. So it could be one of the pins is sending the wrong signal.

EDIT: if you put 400 speed film in block two should be black OOXXO. Since the second block is black, if it reads as 400, then its most likely a bad connection for that pin. If its still reads two stops low, then ? maybe exposure compensation?

Firestarter · Sep 14, 2018

abruzzi said:
Have you tried other speeds?

I looked at the actual codes (speed is just the first line): https://en.wikipedia.org/wiki/DX_encoding

100 is: XOXOX
25 is: XXXOX

200 is OOXOX
50 is: OXXOX

The difference in both cases is the second block. So it could be one of the pins is sending the wrong signal.

EDIT: if you put 400 speed film in block two should be black OOXXO. Since the second block is black, if it reads as 400, then its most likely a bad connection for that pin. If its still reads two stops low, then ? maybe exposure compensation?

Thanks, that could well be the problem, I will try a HP5 cartridge to see.

Firestarter · Sep 14, 2018

So I put in a 400 ASA and the camera displays..............400 ASA. Thank you abruzzi

I will get a cleaning pen tomorrow for the DX pins and see if that sorts the problem.

shutterfinger · Sep 14, 2018

Ink eraser, pencil eraser both work for cleaning contacts as does metal polish.

Firestarter said:
Think I may be getting somewhere with the meter button. it doesn't seem to be the meter button causing the problem after all. It seems that putting any kind of pressure or twisting motion on the camera top plate in the vicinity of the meter button makes the camera think I have just loaded a film.

Likely insulation between the plate and body may have broken down or has been damaged from excessive, repeated pressure in the area.

Firestarter · Sep 14, 2018

shutterfinger said:
Ink eraser, pencil eraser both work for cleaning contacts as does metal polish.

Likely insulation between the plate and body may have broken down or has been damaged from excessive, repeated pressure in the area.

Thanks, I will try an eraser and see if it helps.

The camera looks like it has spent most of its life in its box so yes permanent pressure from the polystyrene packaging could have caused the problem.

AgX · Sep 14, 2018

Firestarter said:
I will get a cleaning pen tomorrow for the DX pins and see if that sorts the problem.

Not necessarily it is a dirty contact pin thing, but it may be an erractic wire connection as with your door switch.
If am right those contact pins are gilded, so you better refrain from abrasive means when cleaning it.

Poisson Du Jour · Sep 14, 2018

An eraser is the least likely of any methods I would personally use to clean the contacts. Isopropyl alcohol and a bud wiped over all of the terminals is a much better and safer idea.

I suspect your camera has been tampered with in some way for the metering selection button to cause a drive advance. There is no custom function on the T90 that can otherwise change functions like those on later pro-level EOS bodies.

The age of the camera, 30+ years, would also be indicative of a full overhaul service. A lot of these cameras were serviced within the first decade for high battery drain and erratic display driver behaviour.

shutterfinger · Sep 14, 2018

An ink eraser is like a fine contact burnishing tool, equivalent to 2000 grit sand paper approximately; a pencil eraser is like 4000 grit sand paper.
Brass contacts corrode and need burnishing at times. A light pressure with either eraser is all that is needed.
Metal polish works best and is least abrasive. Toothpaste (no water) on a cotton swab may work also.

Firestarter · Sep 15, 2018

Have been looking at the DX pins. They are all the same apart from the bottom 2 on the smaller rack where the pins look hollowed out, is this normal ? I will put a pic here, maybe someone with a T90 could compare for me.

cooltouch · Sep 15, 2018

I'm inclined to agree with shutterfinger regarding your meter problem. There are several flex circuit boards in that camera. One of them might have become abraded enough in one spot where there is contact being made when there shouldn't be. The fact that you can get the camera to do this when you torque the top plate lends credence to this possibility.

Trask · Sep 15, 2018

Firestarter said:
Have been looking at the DX pins. They are all the same apart from the bottom 2 on the smaller rack where the pins look hollowed out, is this normal ? I will put a pic here, maybe someone with a T90 could compare for me.

View attachment 208065

The two “hollowed out” pins on your camera are identical to the pins in my T90. While I haven’t used the camera recently, it has always worked properly in the past reading ISO. Though I often bulk load and set the ISO manually. But — I don’t honk those two pins are the source of your problem.

Firestarter · Sep 19, 2018

cooltouch said:
I'm inclined to agree with shutterfinger regarding your meter problem. There are several flex circuit boards in that camera. One of them might have become abraded enough in one spot where there is contact being made when there shouldn't be. The fact that you can get the camera to do this when you torque the top plate lends credence to this possibility.

Had a chance to remove the top plate today for a closer look and I have found the problem. It was simply a dry solder joint on the corner of the flexible circuit that has the meter mode button. So when I was pressing that button or putting pressure on the top plate in that area it was breaking or causing a circuit fooling the camera into thinking a film had just been loaded. A quick tap of a soldering gun and it is perfect now.

Trask said:
The two “hollowed out” pins on your camera are identical to the pins in my T90. While I haven’t used the camera recently, it has always worked properly in the past reading ISO. Though I often bulk load and set the ISO manually. But — I don’t honk those two pins are the source of your problem.

Thanks, at least I know that is not the issue. As above I now suspect a dry solder joint somewhere, I will delve deeper when I have the inclination. For now I'm not too concerned as I rarely rate my film at box speed anyway. Would like to get it sorted though so the camera is 100%.

Thanks for the pointers everyone

cooltouch · Sep 21, 2018

Cool, glad to read that you found the problem. Cold solder joints are the first thing I look for, mostly since they're one of the few things I can puzzle out when confronted with a maze of electronics.

CMoore · Sep 21, 2018

cooltouch said:
Cool, glad to read that you found the problem. Cold solder joints are the first thing I look for, mostly since they're one of the few things I can puzzle out when confronted with a maze of electronics.

I work on guitar amps a little bit.
A guy, the proud owner of a Blonde Bassman that was originally purchased by his father, brought me his amp. He said the volume knob stopped working all of a sudden.
Cold Solder.?.....No.
It was NO Solder.
One of the wires to the Volume Pot was NEVER soldered at the Fender Factory.
We are talking, maybe, 1962.!
All these years there was enough of a crimp to keep making contact between wire and lug.....eventually it gave up.
I soldered it...For The FIRST Time...and all was well.

abruzzi · Sep 21, 2018

CMoore said:
It was NO Solder.

I was troubleshooting a bad camera (video) at work. The camera was mounted to a motorized pan/tilt/zoom and the PTZ had its own wire connectors for the camera SDI output, so as not to stress the cables or the connector on the camera. I pulled the SDI board on the PTZ, and it was mostly surface mount components, but there were two or three through hole capacirtors, and none of them had solder and were only held in place because the leads had been bent enough that they didn’t fall out. It was an $800 card. I was able to convince Panasonic to replace it for free. (I wasn’t going to try soldering it because then any hope of a warranty would be gone.)

cooltouch · Sep 21, 2018

No solder. Amazing. I'll bet that old Bassman has a bit more gain now than it used to. Or at least, it should.

CMoore · Sep 22, 2018

Well, it is just like the wiring in your home. Nothing is soldered, it is all just a Mechanical Connection.
These old, hand-wired heads were similar.
20AWG solid core wire, tightly wrapped around the lug of a pot, and then given a squeeze with the needle node pliers.....it would play "normally" until that connection came loose.

Canon T90 issue........not the usual one though !

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