Tektronix 2465A A5 battery backup - Page 1
Forum section: electronics / testgear

author: tridentsx
author_rank: Regular Contributor
timestamp: September 01, 2014, 07:14:38 am
content: I am recapping a 2465a tektronix scope to see if that will bring it back to life. I have a question about the long life lithium battery on the A5 board. Is there a standard procedure to replace it ?It seems mouser are selling replacement batteries,http://www.mouser.com/ProductDetail/Eagle-Picher/LTC-7P/?qs=MQ89PJz411eJdMnu%252btznWw==I would assume that there are some test point I can connect a battery to while doing the replacement ?There is another old thread I didn't want to revive it since it didn't have any conclusion and was polluted with 2465b pictures etc confusing newbies like myself ...

author: David Hess
author_rank: Super Contributor
timestamp: September 01, 2014, 12:59:44 pm
content: Quote from: tridentsx on September 01, 2014, 07:14:38 amI do not think there is a dedicated test point however there are several spots where you could connect an auxiliary supply to power the battery backed up SRAM while changing the lithium battery. I would use the junction of CR2370 and CR2371 shown on schematic 1. 3 x AA cells in series would make a good auxiliary source.

author: iDevice
author_rank: Regular Contributor
timestamp: September 01, 2014, 06:35:05 pm
content: There are indeed no tespoints but it can be done like David said.I would refrain using a PSU or even standard batteries in series though.Standard batteries means using a holder and some cheap crappy ones are prone to contact micro-interruptions when you move of bump them. You also have the risk of one cell popping out of the holder while manipulating it.If that happens when the original cell is unsoldered, you are toasted...Same thing with an external PSU with banana cables, mini-grabberss, etc.What I do is use a Lithium cell with leads, like the ones meant to be soldered directly to a PCB, and I solder a 5K resistor on one end in series with an isolated wire and a second wire on the other end.Then I solder both wires to the scope board on a place where tracks lead to the battery.But you must connect after the original battery 10K series resistor on the PCB, not directly to the original battery.That way, you are protected for any short you make when unsoldering the original and you won't load any of the two batteries which will be at different voltages.Final precaution, don't ever do that with the board connected to anything, particularly earth.Your iron may be earthed so if your board is earthed because still connected to scope and scope switched off but still connected to grid, when you will touch the positive of the battery with the tip, you will short it through the earth loop.

author: David Hess
author_rank: Super Contributor
timestamp: September 01, 2014, 09:09:49 pm
content: Quote from: iDevice on September 01, 2014, 06:35:05 pmI made the cheap battery holder mistake once. Since then, I solder the AA cells together with short jumpers and insulate the ends of the pack so that it cannot short out on something. The lesson about AA cell shorts involved a fire caused by two NiCd AA cells shorting out on a whip antenna.I have managed to learn the grabber/alligator clip/banana jack lesson without losing any calibration data. I have a number of floating output power supplies and if I used them for this, I would use the binding posts as, well, binding posts and solder the jumpers temporarily into the circuit.QuoteDouble check your grounds. Then check them again.Actually I am paranoid enough that last time I did this, I used my multimeter to verify galvanic isolation.

author: Bryan
author_rank: Frequent Contributor
timestamp: September 01, 2014, 10:33:10 pm
content: Quote from: iDevice on September 01, 2014, 06:35:05 pmThe super cautious can always unplug the iron before soldering. Would be enough heat in the tip for quick soldering. Advantage being I suppose the initial grounding would avoid any ESD.