|Re: HP-41C flakiness|
Message #19 Posted by Randy on 15 Apr 2013, 5:23 p.m.,
in response to message #18 by W_Max
Sometimes old capacitors has notable DC leakage. In that case, in simple words, they "stolen" power from the main circuit. Side effect of this failure is relatively fast battery discharge and CPU glitches. But anyway - if electrolytic capacitors are more, than 30 years old, all of them needs replacing.
While electrolytic capacitors do dry out over time, especially when subjected to high ripple currents, this is not the case with the capacitors used in the HP41. Further, the capacitors used in the original 41C and CV's designs were hermetically sealed tantalum devices. In my years of personally repairing many HP41's, I have yet to see a leaky or outright defective hermetic tantalum.
"When I press "ALPHA" key - display goes blank from the right side for a tiny period"
That is not a soldering problem, it is one of mechanical deformation of the LCD. If the display is mounted too low (and this is easy to do), pressing of the PRGM or ALPHA key will deform the pc board which then places pressure on the display driver and LCD directly causing the display anomaly. The proper mounting procedure is mentioned in the service manual which requires the placement of the display as high as possible to avoid the mechanical interference. The same thing can occur as well on the left side with the ON and USER keys.
This problem was mis-understood early in the 41's development and it was thought it was just keyboard deflection. Early 41C and CV case frames had extra heat stakes along the top row of keys to prevent this anomaly. HP later decided that is was not a problem, it did not affect usability and the extra stakes impacted assembly and soldering of the display connections so the stakes were eliminated. HP also later changed the design of the LCD/driver clamps which helped with this issue.
Quote:Mine as well. I've personally repaired thousands of HP calculators so my postings are real world experiences, not a one off, got lucky repair or second hand something I read on the web.
That all based on my real experience, of course.
IMO, wholesale replacement of components as a troubleshooting method is not a method at all, it will typically introduce more trouble, especially when done by non-experienced persons with less than ideal tools, components and supplies.