Question: My polarity switch appears to be defective. How can I replace it on my own?

Transcription

1 Title: Replacing the polarity switch on an Axopatch 200B. Question: My polarity switch appears to be defective. How can I replace it on my own? Answer: This is a very difficult procedure. We highly recommend that it be done by a Molecular Devices technician. However, a skilled electronics technician should be able to follow the steps outlined below. STEP 1: Remove the top cover by removing 4 screws. STEP 2: Remove the two top side covers, using a sharp object to pry them out:

2 STEP 3: Turn the unit upside down and remove the bottom cover by removing 4 screws:

3 STEP 4: Remove bottom side covers, using a sharp object to pry them open. The front bar is highlighted for STEP 5. STEP 5: Remove the bottom front bar (highlighted above). 4 screws on top; 4 screws on the side (2 per side); and the three screws from the front panel. Bottom screws:

4 Side screws (the two highlighted plus 2 on opposite side):

5 Front panel screws: STEP 6: Remove the top front bar. 3 front panel screws and 4 side screws (2 on each side). Side Screws (2 also on opposite side):

6 3 front panel screws:

7 STEP 7: Turn unit upside down and remove the solder from the polarity switch (14 legs total). Notice 12 legs at the rear of the switch and 2 legs in front.

8 STEP 8: Turn unit right-side up and remove 6 jumper cable connections. 3 from the front panel and 3 from the main board:

9 STEP 9: Remove caps from bottom front panel potentiometers and switches (Lag; meter reading; Mode; Filter; Leak Subtraction). You can probably use a fingernail to pry them out. For testing in one of the upcoming steps, leave the Mode in V-Clamp and the meter reading Vm.

10 STEP 10: Using a straight hex wrench, unscrew the potentiometers and switches. The wrench will need to fit inside the hole opened by the cap.

11 STEP 11: Remove the hex screws and washers still holding the 5 pots and switches attached to the front panel.

12 STEP 12: Remove the cap from the Series Resistance potentiometer by using a small Allen wrench into the small opening on the side of the dial. With the cap removed, use a forked tool to unscrew the Series Resistance dial.

13 STEP 13: Turn unit upside down. Inspect the polarity switch solders to make sure that all solder is gone from the legs. This is a very important step. Take your time to ensure that the switch is no longer attached or you will damage the PCB when prying out the switch.

14 STEP 14:

15 Turn unit right-side up. Pry open the front panel (see picture above) and pull the switch out. STEP 15: Clean the holes from the switch on the PCB. Use a solder iron with a Kimwipe. The holes need to be completely free of obstructions. STEP 16: Throw away the old switch. STEP 17: Put the new switch into position. You will need to gently pry open the front panel.

16 STEP 18: Before soldering the switch on, put hex screws back on front panel Series Resistance potentiometer. This will ensure that the front panel is snugly attached before proceeding further. STEP 19: Check top and bottom to make sure that the polarity switch fit into its holes:

17 STEP 20: Solder legs of polarity switch to PCB. STEP 21: Reattach jumpers to front panel and main board (from STEP 8). STEP 22: Before proceeding further, this is a good point to stop and test the functionality of the switch. Using the front panel Holding Command and observing Vm on the meter, make sure that the switch works in the positive (+), negative (-) and OFF positions. STEP 23: Clean the solder joints you make using a sharp scraper and a light metal brush:

18 STEP 24:

19 Replace bottom front bar. Insert side screws first, then loosely attach bottom 4 screws, and finally the front panel screws. Tighten the bottom screws: STEP 25: Replace top front bar. Insert side screw first; then front screws:

20 STEP 26: Make another round to make sure all screws from top and bottom bars are tight. STEP 27: Make sure the wire going from the front panel Scaled Output is in its groove on the side panel. Use some tape if necessary

21 STEP 28: Place the remaining hex screws on the front panel pots and switches.

22 STEP 29: Replace the dials (leave the Series Resistance last). As you place the dial back on, make sure that its setting is in its lowest position before tightening it. You will have to use one hand to keep the switches from turning as you tighten them (see picture). Put the caps back on.

23 STEP 30:

24 Replace the Series Resistance dial. The first step is to use the forked screwdriver to tighten the dial while using your other hand to keep the zero reading position at the top. Once the dial is tight, use a sharp object (such as the tip of an Allen wrench) to turn the dial completely counterclockwise. Put the cap on and tighten it, again while keeping a zero reading position at the top. The dial in position, before tightening: The forked screwdriver in position:

25 After tightening the dial with the zero position at the top, using an Allen wrench to turn the dial completely counterclockwise:

26 Tightening the cap while keeping a zero position on the dials:

27 STEP 31: Replace the bottom cover. You may need to pop it in first: STEP 32: Replace all side panels by popping them in. Make sure that the side screws are tight or you won t be able to put the panels in.

28 STEP 33: Replace the top cover and you are done:

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