VAX 11/730 quickie

tony duell ard at
Sat Feb 20 08:46:31 CST 2016

> > Of course I don't know mine works, I need to get a working TU58 tape...

Perhaps I should have been a bit clearer, it does pass the console POST,
then gives read errors on both drives (as there is no tape in them), then
gives the ROM> prompt. So mine is getting further than yours, but until
I have a working microcode tape, I don't know how much of the rest of 
the machine is good.

> That's good to know on the LEDs. Yes I checked the PSU first; three
> red lights. The baud rate switches are set for 4800 - the default.

OK... Sounds like your PSU is OK. But worth checking the voltages 
just in case!

> think I have the console cable correct - and just in case I buggered
> the Rx/Tx I tried it with them swapped. Nothing. Never so much as a

When I was routing the cables in my machine (as I was rack-mounting it, 
I had to put the R80, RL02, console, remote diagnostics, TS05 and
DMF32 cables all in at once), I actually buzzed out a few non-ground
connections between connectors on the distibution panel and IC pins
on the right board (from the printset) just to be sure I hadn't got them
mixed up or turned over or anything. It might be worth just checking
that the RS232 chips on the WCS board do connect to the pins on the
terminal you think they go to.

I don't want to 'teach you to suck eggs' (especially since I think you've
been doing this longer than I have) but bitter experience has taught me
that checking 'the obvious' as you go along means you only have real
faults to trace.

> Anything you can tell me about  the POST on your machine - the timing
> - what appears on the console and when etc. - would be helpful.

I will turn mine on later to check. IIRC it prints the first 4 or so characters of
the header line, then pauses (RAM check I think), then the rest of the line,
then the device error messages with a short pause between them, then
the ROM> prompt (from which you can only enter ctrl-C to try to re-read the
tape). One of the manuals on bitsavers (I think it's the diagnostic manual)
explains this, and mine seems to do what the manual says.

Have you checked signals round the 8085 yet? Is it being held reset? Is it
clocking, accessing ROM, etc?

> I plan to use an Arduino-based TU58 emulator when the time comes =
> although I would like real working TU58s too!

I am more interested in having an 'original' machine than a machine to
run VMS on :-). What I mean by that is that I do want to have the TU58
working, rather than some replacement for it. I have replaced the drive 
pucks, in fact I've just been turning another pair for my standalone 
TU58 (which I will use to write a console tape if I can ever find a good
cartridge). The console tape I have has dropouts, is shedding oxide,
etc. The read waveform looks horrible.

I have socketed the 8155 I/O chip in both TU58s (11/730 CPU and 
standalone). If I pull it, I can ground pins on the socket to select
a drive, start the motor, control speed (normal or seeking), direction
etc. I can then use a 'scope on the output of a read amplfier or
a logic analyser around the data separator to see what is going
on. Just got to keep an eye on how far the tape has gone so I
can reverse it before it runs off the end.

If I was going to use a solid-state replacement for the tape I would
probably use the original controller board, put the 8155 on a 
daughterboard plugged into the 8155 socket on the controller, 
use the port pins of the 8155 to link to some kind of flash memory
device and re-write the 8085 firmware. At least then it would be partly
the original. Using a processor with more components than the rest of
the machine (perhaps I exagerate...) seems a bit silly.


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