PDP 11/24 - A Step Backwards

[Rob Jarratt]

Its 600mV, but it is more of a spike than a ripple. Here is a trace: https://rjarratt.files.wordpress.com/2022/03/pin-1-5v-ripple.jpg

Regards

Rob

> -----Original Message-----
> From: Wayne S <wayne.sudol at hotmail.com>
> Sent: 28 March 2022 23:15
> To: rob at jarratt.me.uk; Rob Jarratt <robert.jarratt at ntlworld.com>; General
> Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
> Cc: Chris Zach <cz at alembic.crystel.com>
> Subject: Re: PDP 11/24 - A Step Backwards
> 
> How bad is the ripple?
> Anyone on the list know what’s acceptable?
> 
> 
> Sent from my iPhone
> 
> > On Mar 28, 2022, at 14:46, Rob Jarratt via cctalk <cctalk at classiccmp.org>
> wrote:
> >
> > 
> >
> >> -----Original Message-----
> >> From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Chris Zach
> >> via cctalk
> >> Sent: 28 March 2022 20:57
> >> To: cctalk at classiccmp.org
> >> Subject: Re: PDP 11/24 - A Step Backwards
> >>
> >>> I don't think the CPU is working at all. The reason being that there
> >>> is absolutely no LED activity. Including an LED that is supposed to
> >>> indicate a clock. Having hopefully eliminated all the power voltages
> >>> it left me wondering if there was a fault on the CPU or in the PSU.
> >>> Having had activity on those LEDs recently it seems most likely that
> >>> it will be the PSU, particularly as *something* in there blew up.
> >>> The only signal that I can identify that seems likely to have this
> >>> kind of effect is LTC, but I don't know enough about LTC to know if
> >>> its absence could cause the CPU board not to work at all, although I
> >>> see above that you think it unlikely. I suppose the fault could be
> >>> something I can't see on the CPU board, particularly as there do
> >>> seem to be some quite large spikes, otherwise I am not sure if there
> >>> is anything else from the PSU that could prevent the CPU getting going.
> >>
> >> I'm on a nice long train trip right now but I recently got my 11/24
> >> running again. One thing that baffled me was it would not do anything
> >> on the serial port. No ODT, no nothing.
> >>
> >> Turns out you really need to make sure the slots are filled properly.
> >> The CPU top, then the memory map, then for the next 4 boards one has
> >> to be either a properly configured MS11-PL (the 128kw board) or the
> >> memory boards specific to that type of 11/24. Or you have to put
> >> G7273's in the CD slots.
> >>
> >
> > I have been reluctant to put everything back in, in case the PSU fries
> something. And the ripple I noticed is certainly something that bothers me.
> Previously I had a burning smell from the memory board. I have since
> replaced all the electrolytics on the memory board, but I have not tried
> putting it back in the machine since. Just checking my notes, it seems I have
> had *intermittent* lack of activity on the CPU LEDs before, so it may be
> worth trying to put everything back in, although the ripple makes me
> hesitant to do so. For the record, right now I have only the M7133, M7134
> and G7273 installed.
> >
> >
> >> Next you need proper devices or G7273's in the next two slots and a
> >> proper terminator in the left sockets of the last slots and a G7273 in the
> center slots.
> >> Only then will ODT work.
> >>
> >> Another oddity is that the 5.25 inch box has +5 and +12 I think and
> >> the
> >> 10.5 has +5 and +15. There are different memory boards that work in
> >> one and not the other, or both depending on jumper settings that have
> >> to be right. Unibus drives me bonkers sometimes with the number of
> >> different voltages requires (+5, +12, +15, +20, -15, etc....) It
> >> doesn't help that the +15 and +12 are on the same pins.
> >>
> >> Plus it's possible someone screwed with some switches, make sure they
> >> are set properly (ie: default is a good start).
> >>
> >> If you're still stuck next week drop me a line and I'll fire up my
> >> 11/24 and see if I can replicate your failure.
> >>
> >>>
> >>>>
> >>>> The first will tell you that i) the CPU is basically functional,
> >>>> executing
> >>> micro-
> >>>> instructions, etc; ii) that the bus is basically functioning (for
> >>> master-slave
> >>>> cycles; DMA and interrupts will remain to be checked out); iii)
> >>>> that the console port is working. (Yes, on the KDF11-U, the console
> >>>> is on an
> >>> internal
> >>>> bus, and so in theory a machine could have the ODT 'front panel'
> >>>> working, _and_ still have a problem with the bus, but depending on
> >>>> the exact details of said problem, maybe not.)
> >>>>
> >>>> So, hook up a console, set the machine to 'halt', and power on. Is
> >>>> console ODT working? If so, congrats, you win, go to stage ii) below.
> >>>
> >>> I had a console attached. There is nothing on the console. When I
> >>> first got the machine I did get output on the console. But that was
> >>> before the PSU first failed on me, which is quite a few years ago now.
> >>>
> >>>>
> >>>> If not, you have a reduced area in which you have to investigate -
> >>>> and
> >>> you'll
> >>>> need a 'scope of some kind to make any progress. (If you don't have
> >>>> one, you're SOL. Get one.). In order i) is the CPU's internal clock
> >>>> (and thus, probably the microcode) running? (At this point you will
> >>>> need to consult
> >>> the
> >>>> "PDP-11/24 System Technical Manual", EK-11024-TM.) If so, is it
> >>>> trying to
> >>> talk
> >>>> to the console's registers? (See Section 4.6 of the TM, "Internal
> >>>> Address
> >>>> Decode".) If so, is the UART working properly? (4.7 of the TM,
> >>>> "Serial
> >>> Line
> >>>> Units".)
> >>>>
> >>>> If so, console ODT is running, you're now at stage ii): you can see
> >>>> if the
> >>> CPU
> >>>> will run. Deposit a 0777 ('BR .') in a likely location (I usually
> >>>> use
> >>>> 0100 or 01000); read it back to make sure the write succeeded. (If
> >>>> not,
> >>> likely
> >>>> either the UNIBUS or the main memory has a problem.) Start the
> >>>> machine; the 'Run' light should come on - if you're lucky!
> >>>>
> >>>> Depending on which bin you wound up in, further assistance s
> available.
> >>> :-)
> >>>>
> >>>>      Noel
> >>>
> >