Pentax F 70-210 Disassembly and
I was going to buy this used lens for
$80.00 when it was discovered the focus was jammed.
The manager of London Drugs gave me the lens when they decided it wasn't
I decided to attempt a repair.
Here the lens mount is removed after drilling out one screw.
I didn't damage the threads and I have a replacement screw.
It took some effort to get this far, including
drilling out the screw whose head was stripped by a Philips screw driver.
I could not loosen the screws holding the zoom ring. After ruining
two (guaranteed) Philips drivers I learned a
JIS Crosspoint driver was necessary along with a temperature of 450 degrees
F to release the thread lock
holding the screws.
After getting a
JIS Crosspoint screwdriver
from Micro Tools and using a soldering
iron to heat the screws
the rest came apart without too much effort.
This was the cause of the focusing problems. This
lever transfers the motion of the zoom ring to
the inner zoom tube. The screw had come out. It may have happened due to dry and dirty
on the zoom tube which made it very stiff.
The loose screw had become lodged in this hole
in the focus tube locking it solid.
I had to remodel a set of tweezers to pull out the firmly stuck screw.
The "Information Brush" shown here
will have to be replaced.
I'm not sure if I mangled it during disassembly or if the damage had already
been done by the loose screw.
Anyone attempting to disassemble a similar lens should remove this fragile
contact plate first.
I have 22 photos of the disassembly which should
make it possible to turn this back into a working lens.
After replacing the contact plate and giving the lens a clean and lube
it should make many more great photos.
Well I finally got a reply from Pentax Canada
after ten days, two emails and a phone call.
The bad news is that the mangled "Information Brush" is no longer available
The part has dual contact brushes and five were still intact so I re arranged
them and with some
difficulty soldered the tiny pieces into the correct position and straitened
On the first test the tip broke off of one, probably it was cracked.
That put paid to my attempt at repairing the information brush.
This is an attempt at fabricating a new information
The wires look huge in these macro photos but they are quite fine and
somewhat springy stainless steel.
Will it work? ... to be seen ...
There were a few minor disassemblies required
during the reassembly to get parts in correctly.
But here it is, back together and waiting for my Pentax *ist DS to arrive.
I tried the repaired lens on my new DS and
- it did not work. Well it sorta tried. It would some times
auto focus but the diaphragm wouldn't move and there
was no f stop indication or any other feed back
from the lens. After a couple of attempts I gave up on it as I was having too much fun
with the new
camera and a couple of other new lenses.
I decided to have another go at this. Thought the problem might be the electrical contacts under the
lens mount so took off the mount and carefully adjusted and cleaned the contacts.
After managing to not quite lose the tiny springs several times I managed to carefully reposition
and reassemble the mount.
SUCCESS!! It Works! Everything seems to be functioning properly. I
can only hope it continues to do so.
Pentax DS, F 70-210 at 210mm, f6.7, 1/125, ISO-1600
It was very wet and dull this morning. Shot from the carport.