HP Forum Archive 10

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hp85 Tape Gummy Wheel Message #1 Posted by andy on 11 Feb 2003, 10:28 p.m. My hp85's cassette tape has a bad gummy wheel. Any suggestions on what to use for a replacement? Thanks, Andy

Re: hp85 Tape Gummy Wheel Message #2 Posted by Michael O. Tjebben on 12 Feb 2003, 9:43 a.m., in response to message #1 by andy I used some shrink tubing with success. I'm not certain that's the best solution, but it worked for me.

Re: hp85 Tape Gummy Wheel Message #3 Posted by Ellis Easley on 12 Feb 2003, 1:52 p.m., in response to message #2 by Michael O. Tjebben I also used heat shrink tubing on a 9825 tape drive - same cartridge but maybe not the same mechanism. Made the tape move OK but have other problems on that machine. On the 9825 there is a delicate-looking optical tachometer wheel close to the rubber wheel, on the same shaft. I shielded the rest of the mechanism with aluminum foil while I heated the tubing.

Re: hp85 Tape Gummy Wheel Message #4 Posted by Michael Tjebben on 12 Feb 2003, 4:14 p.m., in response to message #3 by Ellis Easley Actually, Ellis brings up two good points: * Do shield the mechanism from the heat! Mine started to melt slightly, because my shield was not so good at first and I had to be VERY careful! * The HP85 has an optical sensor also, and it appears to have some special calibration that has to be performed with an oscilloscope to look for a particular waveform. I don't have that calibration manual, but I think I recall someone else mentioned it earlier, and I may have a copy of a part of those instructions that I can look for, if you get to a point where you've replaced the wheel and still have problems...

Re: hp85 Tape Gummy Wheel Message #5 Posted by andy on 12 Feb 2003, 5:30 p.m., in response to message #4 by Michael Tjebben Thanks... I actually have the original HP85 Assembly Level Service Manual and it has complete instructions for performing that calibration with a scope. So if you need it, let me know. Andy

Re: hp85 Tape Gummy Wheel Message #6 Posted by Michael O. Tjebben on 13 Feb 2003, 2:10 p.m., in response to message #5 by andy I do have some interest in that particular section, Andy. It doesn't have to be the entire chapter, but just that section. What info I have is: Mike, According to the 85B, service manual (June 1983) the problem may be with the tape speed circuit alignment. LED DS1 on the capstan motor assembly and phototransistor CR1 on the tape transport assembly. This would have been disturbed when you remove the capstan motor. ?Without a cartridge inserted, run the Tape Speed Test from the Service ROM. If the message {TAPE STALLED} appears proceed with step k to reposition the phototransistor? If you have an o?scope measure at tp-4 (upper tp lower left corner of tape pca) you will need to active the drive if you do not have the service ROM (I do not have a copy) set the scope as followed: 10usec/div, 2 v/div, ac coupling --you should see 3 cycles of a sine wave the negative portion is limited. The positive peak should be at least 2.5 v and the negative peak should be a least 2v. Reposition phototransistor CR1 until the desired waveform is obtained. If you don?t have a scope then I guess you can try it ?hit or miss? Another interesting note ?if the customers computer can read tape cartridges that were reordered on the same computer but cannot read cartridges recorded on another computer the tape head maybe out of alignment. Align or replace tape drive assembly. Be sure to inform customer that the computer may no longer be able to read tapes previously recorded on that computer? Hope this helps Regards, JR My problem is that I haven't attempted this, because I don't have Service ROM. Hence I'm VERY curious if your information gives me some clues as to how I might "fudge" or "klude" this step. Thank you, Andy. -Mike

9825 problems Message #7 Posted by Richard Freeman (Australia) on 13 Feb 2003, 12:43 a.m., in response to message #3 by Ellis Easley Ellis I noticed you said you have other problems with your 9825 - Tape drive ? if I could be curious what problems are you having ? I have been trying to fix my 9825 Tape drive and despite finding and fixing a couple of problems still seem to have more somewhere. Perhaps we could compare notes ? Regards Richard Freeman

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