My TU58 again

tony duell ard at
Mon Jan 18 10:40:12 CST 2016

I think I have had a most instructive day. I did what I should have done a lot earlier and connected
a (cheap, built from a Velleman kit) DSO to the output of the read amplifier in my TU58. That's
pin 6 of the CA3130 at location E28 if you are trying to follow along in the printset, The printset
indicates a wobbly waveform there marked 5Vpp. My little DSO can display the peak-peak
measurement of a waveform.

I started by cleaning the heads and demagnetising them (with one of those mains-powered
electrmomagnet things). Of course I unplugged the drive from the controller before doing that
in case the induced voltage was enough to damage things. 

Remember I have removed the 8155 from the controller board and fitted a socket, I have used
jumper wires there to start and stop the tape, change direction, etc without the 8085 part getting
in the way.

I have what appears to be a new TU58 cartridge. With that in the drive I get a steady (and
clean-looking) waveform of about 3.6Vpp. Low, compared to the value in the prints, but I suspect
high enough to work. 

Then I tried my console tape. It goes all over the place. Sometimes 4V. Sometimes under 1V. And
it is anything but a clean signal. There were times when it was just a little ripple. As I understand it
there are no gaps in the formatting of a TU58. Certainly not ones that last for several seconds 
at normal tape speed.

 Worse than that, when I put the new cartrige back in the ampltude was significantly lower, around
2.7V. It came back when I cleaned the head again.

My conclusion at this point is that my console tape is suffering from major dropouts and is shedding
oxide. So now I need to get a good tape (maybe the new one I have), fix the standalone TU58 and
dump the console tape image onto it.

Or does anyone have any other ideas or comments?


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