ksc@cbnewsk.att.com (kenneth.s.cobler) (02/08/91)
To ALL interested parties: Here are the jumper settings for the unix pc /3b1 and how you can manipulate them if you are trying to isolate a memory failure on the 3b1 motherboard. This information originated from the Pete Fales posting. Pete's posting plus some experimentation on my part, when I was experiencing a memory failure while upgrading my 1M to 2M, lead to the table below. NOTE: This is not an exhaustive guide for 3b1 memory problems, just FYI. Excerpt from Pete Fales posting: > The memory on the 3b1 motherboard is divided into 4 banks of 18 chips > each. These banks are selected using the RAS lines on the > DRAMS. You can verify this with a continuity tester, noting that > all the RAS lines in each of the four rows of two chips are connected > together. The banks are numbered 0, 1, 2, 3 with bank 0 the closest > bank if standing in front of the 3b1 (thus, bank 3 the furthest from > you). > > The jumpers at 11H control the RAS decoding and are wired like this: > > ----------------- > +5 Volts o--R 145--o----| A1 | > | | |----- RAS3 > LA2 o---JR5---o | | > | |----- RAS2 > +5 Volts o--R 144--o----| A0 | > | | |----- RAS1 > LA1 o---JR6---o | | > | |----- RAS0 > | Decoder | > ----------------- By looking at the decoder we note: INPUTS OUTPUTS ---------- ------------ A1 A0 RAS-enabled -- -- ------------ 1 1 RAS3 (bank 3) 1 0 RAS2 (bank 2) 0 1 RAS1 (bank 1) 0 0 RAS0 (bank 0) My factory installed 1M 3b1 has R145 and jumper JR6 installed. With R145 we are holding decoder input A1 to a logic 1. With JR6 we are letting the logical address line (LA1) drive the decoder input A0; thus, A0 will enable RAS3 when LA1 is 1 and enable RAS2 when LA1 is 0. Looking at this I was able to construct a table which would allow me to configure a 1M 3b1 out of any 2 banks of memory. INPUTS OUTPUTS ---------- ----------- A1 A0 RAS-enabled -- -- ----------- 1 LA1 bank 3 & bank 2 (factory shipped 1M configuration) 0 LA1 bank 1 & bank 0 LA1 1 bank 3 & bank 1 LA1 0 bank 2 & bank 0 Note: 2M configuration has LA2 as the input to A1 and LA1 as the input to A0. By trying different configurations I was able to isolate down to which bank of RAMs went bad. Luckily it was a bank they I had installed (turns out a bad solder joint on a dip socket for the extra memory). Don't forget to move the following jumpers that tell the system how much memory is on the motherboard (1M or 2M). Excerpt for Pete Fales posting: > The second type of board can be configured for either 512K, 1MB, > or 2MB. This is what I have. There are two banks of jumpers/resistors > near 12B and 11H. If you have a 1MB system, these should be > configured as follows. > > 1 MB system: > > o--R 145--o 1K resistor o---JR1---o Empty > | | > o---JR5---o Empty o---JR7---o Empty > | > o--R 144--o Empty o---JR8---o Jumper > | > o---JR 6--o Jumper o---JR9---o Empty > | > o--JR10---o Jumper > > Converting to the 2MB system involves moving JR10 to JR9, removing > R145, and installing a jumper JR5. > > 2 MB system: > > o--R 145--o Empty o---JR1---o Empty > | | > o---JR5---o Jumper o---JR7---o Empty > | > o--R 144--o Empty o---JR8---o Jumper > | > o---JR 6--o Jumper o---JR9---o Jumper > | > o--JR10---o Empty Hope this helps someone. Let me know how it goes. I will also post Pete's original posting. Ken Cobler AT&T, Room 2G-331 2000 N. Naperville Rd. UUCP: ...att!ihlpm!ken Naperville, IL 60566 Domain: ken@ihlpm.att.com work: (708) 979-4521