|Re: HP-67 Read Error|
Message #5 Posted by Randy on 31 Mar 2013, 9:36 a.m.,
in response to message #1 by Matthew Richards
Quote: They are hermetically sealed tantalums. Never a problem. Jedi mind game: These are not the bad capacitors you are looking for.
I see 3 very small silver metal barrel caps on the card reader board.
Quote:Wrong. Red dot side = +. So now your replacement caps are questionable. I would re-install the originals correctly as they are virtually never the problem, it is almost *always* mechanical. FWIW, in HP land, the square PC pad is + or pin 1.
...The red dot was the neg side, right?
The correct o-ring size is 005. 7/64" ID, 15/64"OD with 1/16" thickness. Installing it on the wheel expands the OD to the correct 0.250" - the same diameter as the base of the metal shaft extending from the black plastic worm gear.
Refer to this article: HP-67 Internals
You can confirm proper switch action with an ohmmeter. With the plate attached with at least the four upper screws, remove the processor board and connect your ohmmeter to one of the connections marked Gnd these locations:
HDS/ = card over head
MTRS/ = edge of card detected, start motor
WPS = write protect, edge of card clipped
If the switches do not go from infinity to less than 2.0 ohms with a card inserted past all contacts, insure that the plate is absolutely flat against the case front and it is held with at least the center two and top two screws. The plate *must* be tight against the front for the switches to work correctly.
If the plate is in place and the switches are still not behaving, it would be time to carefully clean the pc board contact pads with a clean pink pencil eraser being sure to remove all crumbs. Do the same for the ends of the leaf switch contacts, go slow and carefully, you do not want to bend anything. The contacts almost never need adjustment, only a light cleaning.