Portable Tektronix 214 - Battery Repair - Page 1
Forum section: electronics / repair

author: CarsonReidDavis
author_rank: Regular Contributor
timestamp: June 13, 2018, 09:08:59 pm
content: I'm in the process of repairing a portable Tektronix 214. I disassembled the scope and removed the batteries. Then I powered it directly with a two 6 volt sources and it seems to work, although there might be some connection problems while disassembled.So I set about getting replacement batteries for the scope. It originally took two Ax5 NiCd packs, but I settled for AA for cost reasons. I had a local shop weld the NiCds because I have been told that soldering directly to NiCds is inadvisable because of reliability problems that can be introduced if the nylon seal is over-heated.I didn't realize until I got the new packs home, but the technician did not weld to a hanging solder tab. Instead he cut a tiny solder tab that just covers the head of the battery and soldered directly to the top. I fail to see how this is thermally distinct from soldering directly to the battery.I have included detailed pictures of the scope, the original packs, the new packs, and some diagrams I drew at this link:https://imgur.com/a/1sSIH3a.Do I need to have these packs remade? I do not plan on opening this unit again after the repair, so I will have no way to monitor corrosion or other problems.

author: KeepItSimpleStupid
author_rank: Regular Contributor
timestamp: June 19, 2018, 07:54:53 am
content: FWIW: {Packs for the 212 which should fit the 214.https://www.osibatteries.com/search.aspx?searchterm=tektronix+212I got mine there. there. At a place of work, I had the 212. There was an engineering change for the charging circuit.That scope will not work at all without batteries.I've heard that some people are successful soldering the tabs. Some vents are located there too.

author: tecman
author_rank: Frequent Contributor
timestamp: June 19, 2018, 03:46:12 pm
content: I can't remember the mAh rating on the original Tek batteries, but a while ago I had to replace them in my 214. I soldered up 2000 mAh AA cells as replacements. Works fine. I believe that they are actually a higher capacity than the Tek originals.paul

author: edavid
author_rank: Super Contributor
timestamp: June 19, 2018, 05:25:53 pm
content: Quote from: CarsonReidDavis on June 13, 2018, 09:08:59 pmThe photo is a little too murky to answer the question. If there's even a small amount of tab sticking out from the cell, that would have been OK to solder. Or maybe they soldered the wire to the tab before welding it to the cell. On the other hand, looks like poor soldering.

author: floobydust
author_rank: Super Contributor
timestamp: June 19, 2018, 07:28:35 pm
content: Soldering can melt or damage the battery's seals. If you use flux, sand it a bit and are lightning fast, I have had no problems.For your custom pack, it looks like off-the-shelf batteries with welded tabs were used, and then soldered by a gorilla.That huge blob on the end takes a lot of heat, enough to melt plastic seals and vents. I would get a refund.Modern NiMh is superior in that you get 2-3x capacity for the same physical size.I would use Eneloop Pro AA NiMh 2,550mAh cells and bump up the charge voltage as I find NiMh doesn't just drop in as a replacement. It seems to need higher voltage to top off a charge like 1.55VpcThere would be room for battery holders, or get a battery pack made by a shop that can do proper spot-welded tabs, or take a MOT and make a welder.

author: edavid
author_rank: Super Contributor
timestamp: June 19, 2018, 07:40:11 pm
content: Quote from: floobydust on June 19, 2018, 07:28:35 pmBut greatly inferior if the scope is only designed to charge NiCds (high trickle current).

author: floobydust
author_rank: Super Contributor
timestamp: June 19, 2018, 08:04:40 pm
content: NiMh rated0.033-0.05Ctrickle currentNiCd rated0.02-0.05Ctrickle currentLooking at the charging circuit, a mains capacitive-dropper with unlimited voltage, so no battery is going to have a happy life in this scope.I'd probably add a simple TL431 shunt regulator to limit the pack voltage. Tek seemed to go with min. component count to keep things small.edit: In low mode, 120VAC+3.3uF gives about 100mA average charging current.

author: CarsonReidDavis
author_rank: Regular Contributor
timestamp: June 26, 2018, 02:19:25 am
content: Quote from: KeepItSimpleStupid on June 19, 2018, 07:54:53 amDo those packs include the little 3A fuses?

author: CarsonReidDavis
author_rank: Regular Contributor
timestamp: June 26, 2018, 02:21:29 am
content: Quote from: edavid on June 19, 2018, 05:25:53 pmUnfortunately, there is absolutely zero tab sticking out from the cell.

author: CarsonReidDavis
author_rank: Regular Contributor
timestamp: June 26, 2018, 02:31:35 am
content: Quote from: floobydust on June 19, 2018, 08:04:40 pmThanks for the advice. I'm pretty new to the hobby; how exactly would I wire it and what would the effect on the circuit be?