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 <[email protected]> > Sent: 28 March 2022 23:15 > To: [email protected]; Rob Jarratt <[email protected]>; General > Discussion: On-Topic and Off-Topic Posts <[email protected]> > Cc: Chris Zach <[email protected]> > 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 <[email protected]> > wrote: > > > > > > > >> -----Original Message----- > >> From: cctalk <[email protected]> On Behalf Of Chris Zach > >> via cctalk > >> Sent: 28 March 2022 20:57 > >> To: [email protected] > >> 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 > >>> > >
