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02-06-2021, 05:30 AM - 6 Likes   #1
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Tutorial: Change Back-up Battery Pentax K-30, K-50, K-500

Quite often the "Seiko MS414FE FL26E" back-up battery gets drained too much and won't hold the date and personal settings anymore!

This happens particular if you leave your Pentax without it's main battery (no matter if Li-Ion or AAs such as Eneloops) for a longer time! The MS414 is a Lithium and if depleted one cannot "wake it up" again". Similar to CMOS batteries on mainbords.

Those batteries have a leakage current of about 0,2 ľA

These two similar 3V Lithium rechargeable batteries work as well:

- MS518SE FL35E
- MS621FE FL11E (this one I have tried with success)

and the:
- MS920T FL27E should work as well, larger diameter but 0,1mm thinner/slimmer than the MS621FE)

If you search for exactly these battery model numbers you'll find them cheap.
I prefer the original Seiko or made in Japan equivalents.

To get to the mainboard you first follow all the instructions given here in the tutorial for replacing the green China-Solenoid against the venerable DSLR Japan-Solenoid:

1. Manual solenoid replacement Pentax K30 / Discharge flash-condenser / Solenoid choice -

2. Then you get the back part off as well and unplug the connector to the mainboard (red arrow):

The green arrow shows the MS414 and a close-up here:

You can see, the space is large enough to actually place the MS920T FL27E there!

All the larger Lithium rechargeable batteries have more capacity which is useful to us because you don't want to unsolder/solder this battery a 2-nd time, the contacts are tiny and really good soldering abilities are needed for this!

I once messed it up and damaged the contacts! This was due because I believed the claim, that this ELNA Supercap:
DCK-3R3E204T614-E would fit as well and purchased it from USA including some great tools such as this XURON 450S ULTRA-PRECISE TWEEZER-NOS which is just great to work with. It was a waste, this ELNA Supercap did NOT work.
But maybe there are K30/50/500s on the market which use it, so I will not exclude this possibility of course.
And yet: Every K30/50/500 I had open until now had only the MS414 inside. Same for older Pentax bodies.

Because the MS621 and the others are thicker, you have to insulate this metal section on the back-part (blue arrow):

If you don't insulate this part, the battery will be shortened and drain, because the backside is PLUS (+)!

Make sure that when you solder the two pins of the battery onto the mainboard that you don't "bridge" Plus and Minus accidently!
The battery is pre-charged and you don't want to drain it right away!

Again: This is for those who are really able to solder tiny contacts.
Soldering the solenoid is peanuts compared to this.

Datasheet for all those Seiko MS-types attached

Good luck!

Attached Images
File Type: pdf Seiko MS414-518-621.pdf (941.0 KB, 17 views)

Last edited by photogem; 02-21-2021 at 01:00 AM.
02-06-2021, 06:51 AM   #2
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You're a braver man than I, Photogem
02-06-2021, 07:37 AM   #3
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Great work Photogem!
And good to hear my experience on the old thread contributed to the release of this new tutorial of yours 😊, thanks
02-06-2021, 09:05 AM   #4
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QuoteOriginally posted by roberrl Quote
You're a braver man than I, Photogem
Well, I have some soldering experience and did very fine soldering.


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