LINCtape/DECtape Head Alignment

Date: Sat, 18 Mar 2017 21:46:21 -0500 From: Jay Jaeger <cube1 at charter.net> Subject: Re: LINCtape/DECtape Head Alignment Curious: How are you measuring the signal from the head? Do you have an honest to gosh differential probe, or are you using some other technique? (If you have a differential probe, then the TU56 manual indicates that you should see 10mv-12mv (the addition of the two paired heads together), so as a first guess I am guessing you are looking at the coils one at a time. The reason I ask is that the TU56 that I use most often has gotten a bit cranky over the years. Generally I can read and write, but I do typically see some errors - unacceptably many, and it *seems* that the longer the machine is on, it seems the more mark track errors I get when running the ZTCC?? diagnostic (test 3). I don't have a differential probe, and the A-B math function on my Rigol DS2072 scope is not anywhere near fast enough (though maybe a firmware patch which I have downloaded will help, but I doubt it will help because their is a lot of HF noise on the signals when measuring voltages this low). However, if I apply a 50KHz low pass filter on the signal on the scope, then sometimes I can see a 5mv per coil signal using an ordinary probe. I say sometimes because the scope seems to have some firmware problems so it isn't consistent in its behavior. (I have downloaded a firmware update that *might* help). I don't really doubt my heads at this point - certainly nothing is open - I can measure each coil at about 1.5 ohms (3.0 ohms across both), but it is something I would like to make sure I know how to do. Also, have you degaussed your heads? If so, how? I ask because some of my symptoms could point that way (I have yet, for example, to test with a tape, have it get worse, then go back with the machine "cold" and see if it gets better - and if it doesn't, that could point to demagnetized heads.) Thanks. JRJ