Minolta x700 light meter problem.

[vodanh]

I have an old Minolta x700. Everything works fine, except the light meter. The over-range LED always blinks, means that there's not enough light, even when I set the largest aperture, 1.7 on MC/ or 2.8 on MD Rokkor lenses. The MC or MD coupler work well. I changed new batteries, but it still didn't work.

I have searched on google and it seems that this is a quite common problem, but there is not much information about that issue. There is an answer on Reddit that said it's the problem of MC coupler, it stuck at the right so the aperture to Minolta system is always smallest, but in my case, MC coupler could move well along with the aperture ring.

Have anyone got this problem and solve it? Or at least know any other information could cause it? People always persuade me to buy new body, but it's not only the problem of taking photo with correct lighting, but also the reason behind the scene that matters to me.

Please help me.

Thanks.

 

[shutterfinger]

So here is a start: https://www.suaudeau.eu/memo/manuels_rep/reflexes/minolta/minolta_X-700_repair_service_manual.pdf
On pdf page 23 is the diagram for the aperture reading ring.
The electrical schematics start on pdf page 49.
Aperture resistors are either wire wound or carbon with a copper or brass wiper arm. The wiper contact gets tarnished or build up with carbon and no longer makes proper contact. Flush it with electrical contact cleaner or 90%+ Isopropyl Alcohol and operate the aperture follower full travel several times.

 

[vodanh]

I've find out that, the light meter of my X-700 still work but I'm not sure that it meters accurately.

At high ISO (400-800), with MC-Rokkor 55mm 1.7, at largest aperture, it still shows some reading like 1 or 2; 2 or 4; or sometimes both 2 and 4. The numbers get larger at smaller aperture like 2.8, but at 4 or 5.6 the over range led starts to blink.

Without the lens, at ISO 200, at manual mode, it shows 8 or 15.

I've cleaned the aperture resistors, it contacts perfectly and travels easily.
So what could be the reason for this?

 

[shutterfinger]

Bad sensor or electronics, cold solder joints.

 

[vodanh]

Bad sensor or electronics, cold solder joints.

Could you please be more specific? Cold solder joints?

 

[shutterfinger]

Solder goes bad and does not make any electrical contact, intermittent contact, or a high resistance contact. Common appearance is dull or crystallized or cracked. All components are soldered to flexible circuit boards. Don't attempt to solder them as you are not familiar with soldering or electronic repair.
Cold solder is a common repair term.