[TUHS] pray for us ! pdp11/34 salvation, continued.

Il Mon, Nov 03, 2003 at 09:49:16AM +0000, asbesto rigurgitava: i quote myself, due to some imprecision (i have a really bad memory, maybe i have some chip to change inside my mind :))) No. the "broken" board is the M7891, 128Kx18 bit MOS memory. The broken chip is E15, a simple SN74LS175. here's the list of the messages in which i first described our problem; the messages start at Tue, 15 Oct 2002 07:46:35 +0000, and they can be find on the mailing list archive here, http://minnie.tuhs.org/pipermail/tuhs.mbox/tuhs.mbox A more precise description of the problem was in a message dated Date: Tue, 15 Apr 2003 00:00:37 +0000: -------- the M7891 board (128K x 18 bit MOS MEMORY MODULE) have the D2 red=20 led light turned ON when turning on the CPU ! this means PARITY ERROR on this board checking the board we found 2 problems: 1) a 74LS175 chip named E15 on our schematic diagram, that seem phisically BROKEN on an edge (there is a fessure on the plastic DIP package). i can't change it now because i don't have a=20 soldering station here to do a nice job, but looking the chip i think it may work... 2) a 5 Kohm 4-resistor bridge named R22 on our diagram, that is phisically BROKEN. this bridge give +5V on signals named DATA OC L, CSR OC L, OC L and X ADD OC L. i changed it with a 4.7Kohm 4-resistor bridge, without any result. --------- Well what i did for now is to cut the pin of the broken chip, without desoldering. I will solder the new chip on the cutted pins, to avoid desoldering the board. Some images of the work in progress here: http://www.freaknet.org/asbesto/pdp11/ Note: just touching the chip, part of the plastic box went out, as you can see in the images. Maybe this can identify a real fault on this chip ? stay tuned! :) -- [asbesto : freaknet medialab : radio#cybernet : GPG key on keyservers] [ MAIL ATTACH, SPAM, HTML, WORD, and msgs larger than 95K > /dev/null ] [http://www.freaknet.org/asbesto IW9HGS http://kyuzz.org/radiocybernet]