Dremel MultiPro Cordless Model 770 Type 1 - Battery Pack Repair

18,903

39

16

Introduction: Dremel MultiPro Cordless Model 770 Type 1 - Battery Pack Repair

About: Retired healthcare executive with these hobbies: Family, RC Aircraft, Tennis, Biking, DIY and Repair, Travel. Educated as Electrical Engineer, spent 45 years in healthcare IT and C-team leadership.

DO NOT TOSS your Dremel Model 770 Type 1 tool just because the nicad battery pack has failed! You can replace the nicads with new ones! Even 'tho the pack is no longer available from Dremel and battery technology makes you want a tool with lithium batteries do not toss this tool. The light weight and easy-to-handle features of this Dremel tool have not been replaced by newer tool models.

When I queried the Dremel tech support team they advised to not attempt a self-repair.

But, a little help from a related Instructables allowed me to open the battery pack. Replacement of the batteries then became obvious.

Resist the temptation to vary from nicad cells since the Dremel Charger No. 758 that came with the tool is designed for nicads only.

Step 1: Open the Battery Pack, 7.2v No. 757

Detach the pack from the tool. There are 4 small tabs which are part of the black case and hold the red battery pack cover. This pic shows 2 of the tabs. All 4 tabs are shown in a later pic. Using a small thin screwdriver or knife blade, gently insert the blade near the tab while pressing on the red finger grip and applying upward pressure. Work around the pack to release all 4 tabs while pressing upward on the red finger grips on the two sides of the pack. Be gentle! If you break a tab, you're in trouble.

Step 2: The Battery Pack Is Now Open

These pics show the open battery pack with the red pack cover removed. Note the 4 tabs on the black cover. Also note the inside of the red pack cover and where those tabs seat when reassembled.

Step 3: More Pics of the Open Pack

Study the orientation of the two 3-cell packs, red pack cover and AA cells. The two 3-cell packs can only be placed in the black case in one direction - so it will be difficult for you to load the packs wrong. Also note the black rubber O-ring inside the red cover. This serves to hold the batteries against the bottom of the pack when assembled. Do not remove the black O-ring. I took pics of the pack at each step of disassembly to help me later.

Step 4: Remove & Replace Two, 3-AA Cell Packs

Study carefully the polarity of the two three-cell packs before you remove them from the black case. Note that the case bottom is marked with polarity. As the two three-cell packs are withdrawn from the black case, note their orientation. A side view of the packs shows how the cells are assembled. Each 3-cell pack provides 3.6v. The switch on the tool delivers power to the tool from one or both packs, thus the 2-speed tool.

When looking at the pack bottom note the silver "buttons" which are the contacts for the tool. These "buttons" may need to be added to the AA batteries by you or your cell supplier. The battery size and pack construction are critical and must be EXACT replacements for the bad ones.

My local Batteries Plus Bulbs store had the AA cells, tools and connector plates to make the replacement packs for me. I left one pack with them to serve as a model. Their price for the packs was very reasonable. Turnaround was one day.

I am now a happier DIYer with one of my most favorite tools performing as good as new!

Be the First to Share

    Recommendations

    • Make it Glow Contest

      Make it Glow Contest
    • First Time Author Contest

      First Time Author Contest
    • Anything Goes Contest

      Anything Goes Contest

    16 Discussions

    0
    yadote1972
    yadote1972

    2 months ago

    And the Angels sing... I was just looking for the right charger for this Dremel Multipro Model 770 Type 1 (mine is blue and looks slightly newer) and wasn't having any luck. I thought you could find anything on Amazon. I have a newer Dremel model but as you noted this one is much lighter and easier to handle but I'm stealing it from a family member and can't find the charger. I will happily order a replacement if I can only figure out which one. I decided the newer style batteries wouldn't work for this model but couldn't decide about their matching chargers. This tool hasn't been used in several years so I thought I better order a new battery too, just in case this one doesn't charge anymore but I guess I won't be doing that. Now it's not a problem. I'll take anything apart at least once! Thanks for all the awesome info and pics. Glad you took the time to do this and share.

    0
    Ben52E
    Ben52E

    3 months ago

    I went full-on lazy, removed the connecting tabs from the internal battery packs, used them to make internal out of (2×) 3 alkaline batteries, held everything together with packing tape.
    Runs fine.
    I intend to keep doing this as my charger is dead.

    0
    MKF5
    MKF5

    2 years ago

    We have the Model 770 and cannot get the battery pack to slide open....how to do this?

    0
    michealespinola
    michealespinola

    Reply 1 year ago

    You need to squeeze the two blue tabs very hard while prying the butt-end away from the black plastic. The blue tabs are also a part of what keeps the butt-end attached, and they have to be depressed inward for release.

    0
    DavidE419
    DavidE419

    1 year ago

    Great explanation, after over 20 years my Dremel is still going strong.
    I have two battery packs, and, so far so good.
    I don't need to change the batteries yet, but, it is well worth knowing how to, when I need to.
    I keep looking on line for spares but they are few and far between.
    I shall save this explanation for when I may need it.

    0
    DanielM1089
    DanielM1089

    1 year ago on Step 4

    How much was the repair? Did you improve the life of the pack? Aka more Milliamps? I'm going to repair mine just curious

    0
    BonzoDog1
    BonzoDog1

    2 years ago

    Thanks for the advice. I have a Dremel 770 (with blue, not red plastic) that's got to be 20 years old and still running on the original ni-cads, which still hold a good charge. If they ever do fail, it's good to know they can be easily replaced. I have an even older corded Dremel for heavier jobs. Both seem better-built than the new ones.

    0
    TheDman22554
    TheDman22554

    3 years ago

    I actually have this exact dremel and the batteries last me about 5 minutes. Thanks for the instructable!

    0
    CarlosP
    CarlosP

    4 years ago

    Great Instructable. I have been rebuilding battery packs for scientific instruments for about 25 years and in spite of what you have been told, you can replace NiCad AA cells with rechargeable NiMH cells available in any hardware store, camera store or drug store. The advantage of NiMH cells (which have the same voltage as the NiCads - 1.2 volts) is that they are more readily available and have higher power density than the NiCads. The disadvantage is that you will get fewer charge/discharge cycles our of them before the battery has to be rebuilt again - about 300 cycles for an NiMH vs. 500 for a NiCad cell. I use the same charger as for the NiCads. i.e. the charger that came with the equipment. Because of the higher power density you will get about twice the run time on a charge as you would with NiCads. I fasten the cells together using the metal strips pulled off of the defective NiCad packs, but if there is room, you can also use hookup wire for this.

    NiMH AA cells come in different power ratings, up to 2800 mAH (Milliamp-Hours). Get the highest rated cells you can find, for maximum run time.

    0
    neopolitan
    neopolitan

    Reply 4 years ago

    yes they operate at the same voltage. they have slightly different charging requirements though and if you want to use the same charger and not have to replace your nimhs in half the time you are as the author pointed out better off sticking with nicd. and yes i have saved several power tools myself as well.

    0
    EToft
    EToft

    4 years ago

    ok. I have to confess...it's Sunday morning, and I was too lazy...at first...to put on real clothes and shoes and run out to the shop. But curiosity got me, and I have time...Church isn't for another hour yet. Anyway, I went and found mine and the battery has a small + and - marked on it. I pulled it apart and put in 4 alkaline AA batts. Held the pack in place, and connected the battery pairs with strips of kitchen foil. Viola. it works...and with good torque. almost full power. Time to 3d print a battery holder.? Thanks for the push in the right direction.

    0
    David Printz
    David Printz

    Reply 4 years ago

    Thx for your comments. I have edited the description to add comments regarding the two 3-cell packs. The black case determines how the packs are loaded - design of the case and the polarity shown on the bottom of the black case dictate the orientation.

    0
    DIY Hacks and How Tos

    Good to know. Repairing a tool is way cheaper than buying a new one.

    0
    David Printz
    David Printz

    Reply 4 years ago

    U bet! Thx for the note.

    0
    EToft
    EToft

    4 years ago

    forgot to ask...can you post a simple diagram of the orientation of the batteries in relation to the battery pack alignment? Thanks.

    0
    EToft
    EToft

    4 years ago

    Thanks!!! I have this tool and the battery charge is not lasting very long any more. I have not been able to find a new pack for a price that makes sense, but I'm not ready to scrap the tool. This will work well for me. I'm also wondering if it might run off of a temporary non-recharge pack (alkaline and black tape). I did an 18 volt drill battery this way way once...2 rows of 3 - 9v batts in parallel...then connected in series to juice the drill. Worked for small stuff, but of course they got a bit hot when you needed a lot of torque for any extended time.