Recent content by jonathanjo

Good-looking PDP11/34a CPU and control boards as a DEC Spares Set They're in the UK and ending today. https://www.ebay.co.uk/itm/285784474691 DEC PDP 11/34A CPU Spares Kit. KD11-EA M8265 Data Path M8266 Control. NEW UNUSED

Hello Friends I've been reading about memory failure modes, especially for dynamic RAM, and wanted to hear from people about what they've experienced most on DEC equipment. Specifically I'm interested in whether there are many "cross-chip errors", or whether most are "single chip". The system...

I really don't want to take out 54 RAM chips and find actually it's something else, so while I'm waiting for some replacement RAM chips ... I've put together a 41256 DRAM chip tester from an Atmega 328, currently running on a breadboard. The algorithm I've using is this: for each pause p in...

Answer appears to be: RAS-only. With system in memory error (or halted in ODT prompt) I'm seeing a 200 ns /RAS every 14.67 us, /CAS staying high. As 14.67 us * 256 = 3.75 ms, this looks like RAS-only refresh doing the 256 refreshes within the 4 ms required period and otherwise idle for RAM.

Hi Friends For context: I'm working on getting a PDP11/53 running: starting with the basic KDJ11-DS CPU board (main thread). As I'm currently getting somewhat unpredictable memory errors, I'm trying to find more details about how the memory subsystem is designed. This board uses three blocks...

Update: I tried a few things without any change: Checked voltage at the board, was dropping almost 0.5V so changed PSU, good 5V measured at the chips All the parts seemed cool, only the AM2908 bus transceivers even warm Tried freezer spray nonetheless Still stuck at this: RAM VPC=024454...

The board looks exceptionally clean, not even fluffballs which makes me think it was possibly never used. I've had for about 20 years, always in good clean dry storage. I'm going to do some double-checking of power supplies and so on and very close visual inspection. I really don't want to...

I did find that: it appears to loop the tests but without output. I ran it, interrupt with CTRL-C, says it ran the tests 257 times with 257 fails. KDJ11-D/S 4.55 Error, see troubleshooting section in Owner's manual for assistance...

Well, I looked for documentation but didn't find anything that explained it as well as you have! Thank you, it's really helpful. Do you know how to run a RAM test which doesn't stop at first fault? It would be good to get a feel for how many chips are faulty. I was considering swapping bank...

Indeed ... was looking for a fast loop so I could see the data write by comparing two scope traces.

The patient is on the bench next to the scope, ODT has been administered, and am trying to run variants of this: 00000000/012700 mov #xx, r0 00000002/000004 xx 00000004/012701 mov #dd, r1 00000006/000040 dd 00000010/010011 q: mov r0, (r1) 00000012/000776 br q Got a few...

The code at 17604666 seems like it's the RAM test code, in ROM: 17604660/020102 cmp r1, r2 17604662/001402 beq .+2 17604664/004714 jsr pc, (r4) 17604666/104124 emt 124 17604670/010320 mov r3, (r0)+ 17604672/105700 tstb r0 17604674/001370 bne .-16 17604676/104027 emt 027 Confirmed by manual...

I connected a momentary switch to ground on the BHALT of the backplane 10-pin: KDJ11-D/S> 031206 @17604666/104124 2 @17604666/104124 22 @17604666/104124 0 @17604666/104124 I see this address is similar to the one in the example from the manual given earlier. Perhaps it's ROM?

Robin -- Thanks for suggestions ... Some further tests ... W25 made no difference. "fairly consistent": RAM VPC=024666 PA=17604666 00000040/125256 <> 125252 RAM VPC=024454 PA=17604454 00000000/177771 <> 177775 RAM VPC=024454 PA=17604454 00000000/177771 <> 177775 RAM...

Progress! I made something to fake the BDCOK_H signal and now hex digit goes from 0 to 1, 2, 6, 3, 4. I saw 9600 baud signals on the oscilloscope (on A0)! Great news: means the board isn't completely defunct. I have lots of "Cisco Console Cable" USB serial adaptors, so I made a converter...