Article 1: GSR Pen whipping problems

Article 2: Repairing pneumo tube assembly

Article 3: Scratchy Thermal Pens

Article 4: Inking Capillary Pens

Article 1:

Are you experiencing any of the following GSR malfunctions?

1. Your GSR pen whips.

2. Your GSR will not balance in manual mode.

3. Your GSR is not responsive in the Auto mode.


Prior to Beginning:

1. Make certain all clothing is protected from ink sprays.

2. Check to make sure finger plates are making proper contact with the GSR cables

See Figure 1

GSR_LEADS.jpg (100796 bytes)

Step 1

Plug cable into GSR input of the storage door and place the finger plates in the calibrator. Do not short finger plates together.

A. Turn the GSR sensitivity up to 10.

B. Center pen

C. Shake GSR cable all over (Fig. 2) to find ant intermittent shorts. Note: Small deflections of the   GSR pen is normal at this sensitivity setting. A problem would be indicated if violent whipping of the GSR pen occurs.

D. If the problem is present, continue with step 2.

E. If no problem is evident, continue running test as normal, noting if any unusual problems occur and call a qualified polygraph service technician.

Step 2

A. Unplug the cable from the door, unplug the interconnecting cable ( gray wire coming from the underside of the door to the module) and plug the GSR cable directly into the GSR module.

B. Again, shake the cable all over.

C. If violent pen whipping is noted, proceed to step 3

D. If problem is gone, the cable from the door to the module is defective and must be replaced. Lafayette Instruments has field replaceable GSR cables. Just call Lafayette Instruments and request a prewired GSR jack/cable assembly. This will enable you to replace the defective GSR interconnecting cable yourself, or if you prefer, send your instrument to us and we can repair it for you.

Step 3

A. Unplug GSR cable from module.

Check to see if the pen whipping is still present; if is is, the malfunction is in the GSR module and repair or replacement of the defective module is necessary.

B. If the pen whipping has stopped, then the GSR cable is defective and replacement is necessary


GSR_LEAD_TEST.jpg (78457 bytes)









Figure 2

  Back to article

This article was extracted from Lafayette Instrument Co. Newsletter  "Polygraph Update Volume 8. No.2 Summer 1993"

Article 2:

Repairing the Pneumo Chest Tube


The following tools and supplies are needed.

1. Bottle of "DURA BOND" general purpose glue (Found at most hardware stores)

2. 8 inch hooked insertion tool fashioned from a piece of coat hanger or similar ridged wire.

3. Small standard flat head screwdriver.

4. Rubber bands #32 sold in most office supply stores.

5. Small metal punch.

6. Hammer.    (Not Shown)

7. Convoluted Tube

wpe7.jpg (17216 bytes)

Note: The following items can be purchased together (except hammer) by requesting a Pneumo Chest Tube Repair Kit Model 76513RK from Lafayette Instruments. Call 1-800-428-7545 for current price and availability.

Using the diagrams, follow the steps below to repair the Pneumo chest tube.

wpe6.jpg (18726 bytes)  (Diagram 1).



wpe9.jpg (23919 bytes)  (Diagram 2)

wpe5.jpg (24181 bytes)  (Diagram 3)

wpe4.jpg (13008 bytes)  (Diagram 4)





wpe3.jpg (23755 bytes)  (Diagram 5)


This article was extracted from Lafayette Instrument Co. Newsletter  "Polygraph Update Volume 5. No.3  September - December 1988"

Article 3:



In the past, Lafayette Instrument fielded calls from examiners who were experiencing problems with pen scratching. The difficulty develops primarily in the older design of X Series and older, electrocardio and (some) GSR pens. The problem can stem from two causes; (1) a maladjusted pen clip and or  (2) a bent pen tip. This article will deal primarily with solution to the first problem.


 (1) The pen clip should be bent so it rests directly over the center of the pen point, (see illustrations below) thereby not putting extreme tension on the pen itself. The purpose is to keep the pen in the cradle while at the same time allowing It to swivel up and down, maintaining constant tension at the point where the pen tip meets the paper. The spring design found on the amplifiers mentioned above was chrome-plated and not very flexible this, therefore, gives it the tendency to break rather easily. If when adjusting the pen clip, it does break; please contact Lafayette Instruments and ask that they supply you with a pen cradle (Model 76310) which has a new zinc plated clip which is more flexible and resilient.

  craddle2.gif (2840 bytes)craddle1.gif (4209 bytes)







(2) The second problem is a relatively easy one to correct. If you notice that a pen tip has become bent and does not rest flat on the writing surface, using your fingertips gently reshape the pen so that It again  looks straight when examining it from both front and side.

hands_pen.gif (4057 bytes)

This article was extracted from Lafayette Instrument Co. Newsletter  "Polygraph Update" Vol., Number & Date unknown


Article 4:


To start the capillary ink flow in the pen, follow the procedure below. It is no longer necessary to use a ‘pen starter’ or ‘duckbill’ to prime the pen.


Ink_bottle.gif (8800 bytes)


  1. Completely remove cap and capillary tube from bottle.



  2. Using a ink filler provided, extract ink from the ink supply bottle.



  3. Fill small bottle to approximately full. DO NOT OVERFILL. Overfilling the ink bottles will not improve ink flow and will increase the possibility of spillage during transit.


  4. Grasp the bottle by the cap as shown in (Step 1) and tighten by rotating bottle with free hand.

    Hand_bottle.gif (8014 bytes)


  5. Gently squeeze the bottle until the ink is forced to the end of the pen (Small bead of ink should form at  pen tip.)



  6. Keeping the bottle squeezed, slightly loosen the cap again by rotating the bottle (Step 2).


    hand_bottle2.gif (6681 bytes)

  7. Release the pressure on the bottle.






Note: On Mechanical Modules: After the pen has been inked the Counter – Balance weight should be adjusted to produce as light a pen pressure as possible for good, consistent inking

This information was extracted from Lafayette Instrument Co. Polygraph Users Manual "Captive Inking" Date unknown


More articles and Helpful Tips coming soon, so please visit us again.

If you have a helpful Tip or Hint on Polygraph instrument operation or maintenance you wish to share please pass it along. I will be happy  to post your suggestions here for all to take advantage of.

You may email your Tips and Hints to polyteck@mindspring.com

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