Tektronix 222PS oscilloscope battery substitution

The problem

At work, we have a Tektronix 222PS "Power Scout" portable digital scope. It can be run from a wall transformer or from an internal gel-cell battery. The original battery finally gave out and I wanted to replace it. The following is from a Usenet post I made to sci.electronics.repair in April 2005:

I am looking for a replacement battery for a Tektronix "Power Scout" 222PS portable scope. The original battery supplied by Tek consists of two Panasonic 4 V 2.2 Ah/20h gel cell batteries glued together and wired in series. The Tek label rates this combination at 8.0 V, 2.1 Ah/10h and gives the part number as 146-0075-00. This same battery may have been used in the other portable scopes like this one, like maybe the 222/A and 224.

The Panasonic part number for each battery is LC-2042R1PU . I can't find this number, but they are the same size, shape, and terminal configuration as the (discontinued) LCS-214P, . (Tek welded some tabs onto the battery terminals to connect the wires to.) I have checked some of the usual suspects, including Power Sonic, CSB, Yuasa/Enersys, and Sonnenschein and none of them make exactly this battery. Power Sonic makes some 4 V batteries that are physically and electrically too big. They also make an 8 V 3.2 Ah battery that will almost fit in the hole except it's just a bit too long (the 5.3"/134 mm dimension).

The solution

I decided to see if I could make the Powersonic battery (model PS-832) fit. I ordered one from Rage Battery in May 2005; with shipping it cost about $25.

Electrical work

The electrical part was fairly easy; I transferred the connector and wiring from the Tek battery to the new one. I soldered the wires directly to the battery terminals and put heat-shrink tubing over the joints. There is a 3-pin 0.156" male header (on the scope's main circuit board) in the battery compartment, and the battery connector matches this header. The connector is not keyed, but the negative wire is in the middle and the positive wire is in both outside positions, so you can't plug it in backwards. The connector is the type where you crimp the individual contacts onto the wires and then insert the contacts into the housing; interestingly, the contacts are fairly exposed on one side of the connector. I think this is by design - the connector shell didn't appear to be broken. There is a small inductor (the size of a 1/4" watt resistor) in the negative wire; I suspect this is for RFI suppression.

Detail of the battery connector. I probably should have made the black wire about half an inch (about 13 mm) shorter.

(all photos link to larger versions)

Mechanical work

There were several ribs on the sides of the battery compartment that needed to be cut away. These served to keep the original battery more or less centered in the compartment. Once these were gone, the battery fit fairly well top to bottom, but not at all front to back. I had to file down the outside of the screw well at the front of the battery compartment to get a little clearance in that direction. I probably could file this screw well down a little more to get more clearance, but so far I haven't tried it.

Views of the modified battery compartment. The black foam squares are original and helped to hold the stock battery in place.

General Top Bottom Front Back

Stuffing it in

I couldn't get the battery to just drop in. I had to loosen up all three case screws (T15 Torx), separate the case halves a little bit, put the battery in, and reinstall the case screws. The terminals need to be bent down on top of the battery as close as you can get them, and the wires need to run between the positive and negative terminals and over the rear screw well. It does go together, and the side cover can go back on, but I only got three out of the four latches on each long side of the side cover to engage. The cover does go on well enough that you can insert the probes in their sockets through the hole in the side cover. Views of the battery as installed.


General	Wire routing	Top latches (leftmost one unlatched)	Bottom latches (leftmost one unlatched)	Probe sockets

Did it work?

Unfortunately I can't say for sure. The scope was still being used on the wall transformer during the time I was working on it, and somewhere along the line I think it got dropped, which damaged the CRT. It still powers up, but the first time I tried it, the display wasn't right. I could get it to light up a little, but it wasn't a recognizable trace or on-screen display and nothing I did helped. I tried it again some time later and could only get a faint green dot right in the center of the screen; I can change the dot's brightness and sharpness with the brightness and intensity controls on the back of the scope, but there doesn't appear to be any deflection happening. When you connect it to a signal source and push the "Auto Setup" button, relays inside the scope click as usual and the "triggered" LED comes on, which is the same thing it did when it was working correctly. It is possible, on this scope, to capture waveforms in the scope memory and download them to a PC; I haven't tried that but it would further confirm that the scope is working except for the display.

Some notes and numbers

If neither the battery nor the wall transformer is connected, the scope will power up by itself when you connect the battery. It doesn't hurt anything but it's a little surprising the first time.
With the open-circuit voltage of the new battery at about 8.58 V, the scope drew about 1.36 A when running. (This is with the presumed bad CRT; a properly operating scope might draw more or less.)
The wall transformer is made by Ault and is marked 328-1059-001 - I'm not sure if that's an Ault or a Tek part number. It is rated 120 V 60 Hz 0.2 A in, 18 VAC 16 VA out.

Disclaimer

This information is meant for people familiar with electronic repair. If you don't know which end of a hot soldering iron to hold, ask someone else for help. I don't get any money or other compensation from any of the companies mentioned.

Last modified Fri Oct 13 03:05:30 CDT 2006