A unpredictable Pentax 645 and a possible cure?

[Kino]

A friend surprised me greatly by giving me a Pentax 645 w/75mm f2.8 kit with 120 and 220 inserts; all in original boxes.

Seems the camera body had been acting up when he put it away and he no longer wanted to deal with the periodic lock-ups that would ensue at exactly the wrong time, so he just gave it to me.

To say I was shocked and grateful was an understatement.

He seemed to indicate it had been in storage for some time, so I started off by loading new batteries and reading the manual. Armed with a dummy load, I tried running the camera through its paces.

The camera would turn on, the LCD worked, the back light on the LCD worked and the LED display in the viewfinder worked.

However, all adjustments being made via the two up and down arrows could only be adjusted UP and would not lower; i.e., the ISO would go higher, but could not be brought down. Same for the EV and Mode settings; all would gain in value, but could not be lowered by the buttons.

So, I took out the Lithium CR1200 battery in the base, cleaned all the contacts in both the Lithium and hand grip with DeOxit contact cleaner and tried again with the old Lithium battery. It worked briefly, allowing adjustments as described by the operator manual, but soon reverted to it's stubborn insistence of only going up in values on the LCD.

In speaking with my friend, he had never changed or had changed the Lithium battery in the camera body. In fact, he was surprised to learn it even existed and could be replaced! Being that he bought the camera about 30 years ago, I thought this might be a good candidate to fix the problem.

A quick order of a new Energizer variant of the battery, an ECR1200, which arrived this morning, saw me place a new Lithium battery in its socket and try again.

After a few attempts of inserting and re-inserting the Lithium batteries and the hand grip, and turning on and off the back light and LCD displays in the viewfinder, the camera now appears to be functioning properly.

Now, probably a lot of the inability to get the camera working after inserting the new Lithium battery revolved around my unfamiliarity with how exactly the camera functions, but I can swear that my success depended upon exercising all the function buttons on the camera and "exposing" the dummy roll when possible.

Now the settings can be adjusted up and down and the camera happily transports the dummy load to completion.

Only time will tell if this is a real fix or if the camera has real electronics issues, but I thought I would post this in case someone else has an issue with a Pentax 645 acting unpredictably.

BTW; I DID offer the camera back to my friend, but he was adamant that he didn't want it back; preferring to keep one of the lenses and hoping to upgrade to a 645N or 645NII, so I thanked him for his generosity.

 

[shutterfinger]

I suspect failing solder joints at one or both battery contacts. The installing/removing/cleaning of the contacts may have worked the joints to where the contact is better but may fail again with usage or time.

 

[wiltw]

Based upon the fact that the camera turned on, and that an assortment of displays properly lit up, I sincerely doubt the issue was battery contact.
That the Up button worked, but the Down button did not, I suspect a build up atmopheric contaminants or simply oxidation of the surfaces of the electrical contact under button Down were to blame.
Working that contact repeatedly, in rapid succession could help in removing surface contaminant or oxidation build up.

In the days before electronic channel control on TVs, the tuner used to use electrical contacts on a rotary control, and one might have to spin the control back and forth to clean contacts of contamination/oxidation. If that didn't work, one might have to call a TV technician who would spray electrical contact cleaner into the rotatory control and then twist the control knob rapidly a number of times, to clean the contacts.

 

[shutterfinger]

In the days before electronic channel control on TVs, the tuner used to use electrical contacts on a rotary control,

So you're familiar with those!
Led displays require the least amount of current to work, the built in meter requires more, and shutter and or aperture solenoids the most.
A weak battery contact may allow 250mA but not the 300mA a slightly dirty contact requires.
Remote controls for home entertainment electronics use a carbon coating on the rubber button sheet that mates with a copper grid on the circuit board when pressed. The carbon coating wears with use causing failure.
Unknown what type of switch Pentax used but I have encountered weak solder joints that will conduct some current but not enough to operate fully, tarnished brass switch contacts, and worn carbon coating on buttons.

 

[wiltw]

So you're familiar with those!
.

I remember black & white TV, rabbit ears, constant fiddling with Horizontal Hold
I remember color TV coming out
I remember monaural home FM, and the advent of FK stereo conversion kits for home consoles
I remember tubes in TVs and amplifiers and swapping out bad tubes

 

[Kino]

Well, it's back to acting up.

So much for a cure. Looks like a shelf queen...

 

[4season]

Good ole rubber dome switches (which Pentax apparently used on the 645N - visible at 1:06 on this video). Can be fixed though shame on them for using them on such a pricey item. Those things caused me plenty of headaches with Tadiran phones, where the hook switches were forever sticking. I doubt that the rest of the switch is particularly dirty or oxidized, in fact it appears heavily gold-plated. But the conductive rubber bit may benefit from being wiped against a clean piece of copier paper, which ought to expose a fresh layer of carbon. Or if you are feeling adventuresome, replace with some other type of switch.

 

[pentaxuser]

Well, it's back to acting up.

So much for a cure. Looks like a shelf queen...

That's a real shame. It's as if you have a fully functioning car that has on the surface only a minor problem. It sticks in the craw to simply write it off but quite what you can do is beyond my "ken"

It's long odds these days as most on the Pentaxforums are digital users but it might be worth asking the question as some "vet" there might have the same problem in the past and either have an answer or be able to give good reasons why what appears to be a little issue is in fact a major issue which cannot be solved or solved only at great expense. Either way it at least eliminates the "there must be a simple fix " nagging feeling that wouId certainly affect me as well

pentaxuser

 

[Kino]

That's a real shame. It's as if you have a fully functioning car that has on the surface only a minor problem. It sticks in the craw to simply write it off but quite what you can do is beyond my "ken"

It's long odds these days as most on the Pentaxforums are digital users but it might be worth asking the question as some "vet" there might have the same problem in the past and either have an answer or be able to give good reasons why what appears to be a little issue is in fact a major issue which cannot be solved or solved only at great expense. Either way it at least eliminates the "there must be a simple fix " nagging feeling that wouId certainly affect me as well

pentaxuser

Agreed. I will at least part it out and get it out of my possession, as it will bother me to no end and I'll have to keep messing about with it until I really destroy it!
At least it has some good accessories someone else can use.