hp-91 transistor substitution
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09-21-2014, 05:12 PM
Post: #5
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RE: hp-91 transistor substitution
(09-20-2014 10:20 PM)Paul Berger (Canada) Wrote:(09-20-2014 05:10 PM)joseaem Wrote: Hi all.From your picture that does not look like a break in the transistor, that looks more like there is a coating of some kind on the back. In any case there are no transistors in the drive circuit for the display. The segments are turned on by ROM 0 through the anode driver chips. The fact that the this segment is on for all digit positions would suggest that the driver is on all the time either due to a fault in the driver chip or in ROM 0. If the anode driver had failed I would expect the segment to come on as soon as you turned on the calculator and remain on, however this symptom could also be caused by a failed ROM 0. You could isolate the anode driver by swapping them if the anode driver has failed it should cause a different segment to be lit up all the time. If it is a segment driver you may be able to get a replacement as I believe this chip 1858-0044 was used in all of the topcats, however the ROM would be unique to the 91. Hi Paul Many thanks for your response. As you indicated, the SSD was drived for two IC 1858-0044, near the display (see picture), this are a special transistor array (4x) as describe in http://www.rskey.org/CMS/index.php/exhibit-hall/130. Next days I'll explore the behaviour of IC's and transistors as I related to JEBEM. I'll say to you soon. Best Regards |
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Messages In This Thread |
hp-91 transistor substitution - joseaem - 09-20-2014, 05:10 PM
RE: hp-91 transistor substitution - jebem - 09-20-2014, 07:17 PM
RE: hp-91 transistor substitution - joseaem - 09-21-2014, 04:10 PM
RE: hp-91 transistor substitution - Paul Berger (Canada) - 09-20-2014, 10:20 PM
RE: hp-91 transistor substitution - joseaem - 09-21-2014 05:12 PM
RE: hp-91 transistor substitution - cruff - 09-21-2014, 11:32 PM
RE: hp-91 transistor substitution - Paul Berger (Canada) - 09-22-2014, 01:55 AM
RE: hp-91 transistor substitution - joseaem - 09-22-2014, 06:36 PM
RE: hp-91 transistor substitution - jebem - 09-22-2014, 07:51 PM
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