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drpeter

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About drpeter

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  1. Scientific literature on the effect of various wavelengths of light on degradation of ABS and similar polymers suggests the following: 1) Yellowing is accelerated by UV light, both UVA and UVB across the spectrum 2) Weakening is similarly accelerated by UVA & UVB but as the plastic ages and yellows, visible light also becomes increasingly damaging 3) Bleaching out of yellowing is due to visible light at the blue/violet end of the visible spectrum 4) Yellowing is accelerated by dark because, particularly in normal indoor lighting conditions behind glass, the bleaching effect of visible light exceeds the yellowing effect of UV light 5) Normal glass filters UVB completely but UVA only partially. Laminated glass/windscreen/windshield glass or UV-filtered glass completely filters out UVA also The conclusion to be drawn from this is that in theory the best and safest way to reverse yellowing without damaging the plastic should be by exposure to bright light in the visible spectrum e.g. bright daylight behind laminated or UV-shielded glass. Note that although the windshield/windscreen of a car is usually UV-shielded, side windows usually are not and the dash of a car in full sunshine might get VERY hot unless it is very well ventilated. Refs. Searle, N. D., Maecker, N. L. and Crewdson, L. F. (1989), Wavelength sensitivity of acrylonitrile–butadiene–styrene. J. Polym. Sci. A Polym. Chem., 27: 1341-1357. doi:10.1002/pola.1989.080270418 Abstract The wavelength sensitivity of unpigmented 100 mil thick ABS exposed to sunlight and filtered xenon are radiation was determined by the sharp cut filter technique based on three types of photochemical changes: bleaching, yellowing and loss in impact strength. Bleaching of the yellow‐colored species formed in the processed material is caused by wavelengths between 380 and 525 nm with maximum color change by the 475–485 nm region. Photochemical yellowing is due to wavelengths between 300 and 380 nm with all wavelengths being almost equally effective. The spectral sensitivity based on change in impact strength shifts from the UV to the visible region as photochemical yellowing progresses. Pickett, James. (2004). Reversible post-exposure yellowing of weathered polymers. Polymer Degradation and Stability. 85. 681-687. 10.1016/j.polymdegradstab.2004.03.008. Abstract The commonly observed effect of weathered polymer samples continuing to change color in the dark was studied in some detail for polycarbonate, styrene–acrylonitrile copolymer (SAN), and various combinations with SAN–polybutadiene rubber graft (SRG) copolymer. All of the formulations became more yellow upon storage in the dark after accelerated weathering, and all behaved very similarly. There was a fairly rapid shift of 1–2b units (as defined in CIELAB color space) over the first two weeks followed by a slower, linear shift that continued for many months. This amount of color shift is enough to be visible to the eye in side-by-side comparisons. Most of the additional color generated in the dark could be bleached by exposing the samples to sunlight through a south-facing window. The samples usually reached the original color after 2–4 days of window exposure. Putting the samples back in the dark caused the yellowing to start up again, although the rapid yellowing often was not as much as the first time. Samples aged under natural conditions outdoors also underwent a small color shift upon storage for 5 months and substantial color shifts after two years.
  2. For what it's worth, the Atari maintenance manuals suggest using (carbon) tetrachloride cleaning fluid for the pinch roller and isopropyl alcohol for the heads.
  3. OK, Thanks, I'll get a couple on order and report back in due course. You guys are brilliant.
  4. OK, so that worked- the drive spins up and busy light comes on with pin 11 grounded. So definitely not a problem further on than the 6532. Does it matter whether it's a 6532P or 6532AP, do you know? And does the second designation printed on the chip below that matter (which I presume is a revision number, e.g. 6532-11, which is what mine says) Most on-line chips seem to have 6532-13...
  5. Hi, I'm hoping for help in resurrecting my 1050 drive. I dug it out for the first time in several years and was pleasantly surprised when it fired up and booted from a disk without incident. Until I tried to do the same again 30 minutes later, since which time it has failed to spin any disk. The busy light does not come on when the catch is flipped down and there is no evident attempt at activity with the stepper motor or drive motor. The drive belt is in place. There is no problem visible to the naked eye with connectors, wires or components and connections on the main circuit board. I've tried reseating all the connectors nevertheless, to no avail. The power LED is on and the power transformer measures correct voltage and works with other equipment. Having downloaded the 1050 field service manual, I've made the following checks: All the voltages in the power supply stage test as normal. However, there is no voltage to the drive motor (zero volts on the red wire whether drive door is engaged or not). The resistances across the drive motor are normal. The diskette sensor switch is operating correctly. The voltages on the inputs & outputs of the diskette sensing circuit integrated circuit U6 also behave as expected. However, on pin 11 of the PIA chip U7 the voltage remains at 3.2 V regardless of whether the door catch is open or closed. I understand that this voltage should fall to 0.1V when the drive is activated. I have reseated the PIA chip, but no difference. Short of swapping out the PIA chip for one from a known good drive, which I don't have, I've run out of ideas. Anyone out there able to help?
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