test-drb

test-drb@ccmp.vtda.org

101090 discussions

by Philip.Belben＠powertech.co.uk

Tony Duell wrote: > I'm pretty sure the teletype is a passive device and expects the other > device to source the loop current. > > 5V should be enough for the transmitter loop (which is just switch > contacts), but I doubt if it would be enough for the receiver loop (more > like 12V or more here) I used a TTY ASR-33 as a printer for my PET years ago. My memory is that if I left the receiver open circuit, i yammered away printing nulls; if I shorted out the loop it didn't. I interfaced it using one transistor - no power supply was necessary. +---------------------- | OUT b |/c -------/\/\/\/---------| NPN TTY |\e PET | -------------------------+---------------------- GND Note: I never interfaced the TTY transmitter - not even for reading paper tape (don't know why not) Philip.

28 years, 3 months

Grundy Newbrain Computer wont power up.

by Andy.Keeble＠Royal-London-ins.co.uk

> -----Original Message----- > From: ard(a)p850ug1.demon.co.uk [SMTP:ard@p850ug1.demon.co.uk] > Sent: Tuesday, May 12, 1998 7:15 PM > To: Discussion re-collecting of classic computers > Subject: Re: Grundy Newbrain Computer wont power up. > > > > > Can anyone help me bring an old British Computer back to life. > > > > Last night I bought a early 1980's Grundy Systems Newbrain "AD" > computer > > from an advert in the local newspaper. > > (See http://www.ndirect.co.uk/~e.tedeschi/picts/newbrain.jpg) > > > > The machine is in good condition, with original manuals, cables, > psu, > > and even some software. > > > > Unfortunately it wont power up. > > I have the Newbrain schematics somewhere if that would be any help. > Unfortunately I don't have schematics for the PSU, but I think that's > a > pretty simple linear unit. [Keeble, Andy] I only had a quick look at it the previous night, but had a bit more in depth look last night. It does look like a PSU problem, and yes the PSU looks straghtforward enough. > > > > Turning on, the LED display flickers and goes blank (although the > manual > > Actually, it's a fluorescent anode display (see the other > thread...)... [Keeble, Andy] Indeed, I only saw a quick flash on power up, and presumed it was led. When I opened it up last night I got a better look. > > says it should do this, although I don't get a test pattern which I > > think I should) On the Television/video output I just get a white > > screen. > > > > Does anybody know if these machines suffered from any common faults? > > Check the PSU. The easiest way to do this is to check the 3 supply > lines > at the 4116 DRAM chips (+5V, +12V, -5V). If any are missing or > incorrect > then the machine won't power up. [Keeble, Andy] The PSU says something like +6v +12v and -13v. I found the +12v ok, but the other two outputs are showing +20v, so I guess its a voltage reg problem. (These are offload values). > Check the inter-board ribbon cables for broken wires (they're solid > core > and break easily). [Keeble, Andy] I will check that, but I suspect I may have already found the fault, due to the high readings from the psu, just hope it has damaged any chips in the machine? > Apart from that, if the PSU is OK, you're going to have to > troubleshoot > this one starting at the Z80 (what is it doing) and working through > the > logic. I don't know of any stock faults on these machines. [Keeble, Andy] I thought before spending hours, I would ask folks on the mailing list, just in case there were any common problems. I used to work in a computer shop in the early 80's and several makes of machines came in with the same fault. We didnt deal with Newbrain back then, so I didnt get any experience of them. If I get the PSU working, and find I need a schematic, would you be willing to scan a copy and email it, or photocopy and post it (I would pay any expenses). There seems to be little info about the Newbrain on the net, and I guess not that many still exist, so it seems a shame not to try and put some effort in trying to get this one working again. > -tony

28 years, 3 months

Another strange z-80 / CP/M box...

by JRichardson＠softwright.co.uk

Ok, whilst on the subject of big old CP/M machines.. I've got an old Philips P3800 machine, in a grey cabinet about 1 metre deep, maybe 80cm high and 40cm wide. Tracking down any info on it has proved impossible so far; has anyone got one of these they could share information about, or know anything about them? It was damaged in a flood a few years ago, the switchmode PSU in it has failed and just gives a whining noise when power is applied - I seem to remember I tried loading the PSU without connecting it up to the system backplane or drives, so I think it really has failed rather than there being a short or anything within the system. The hard drive (I *think* it was a10MB Seagate full-height, sadly my entire collection is a couple of hundred miles away from me so I can't check!) controller board went with a bang when power was applied - can I simply swap in another board from an identical drive in the hope that this'll work, or are boards calibrated in some way to their respective motors? I tried this swapping with another identical drive and the drive span up ok, so maybe it would work... I don't know what state the data on the drive it in though. Other info needed: Tape drive - mine is missing, having been put in another machine years ago. Anyone know what sort it was, and will the system run without it? Cabling - what sort of terminal could be connected to the cables hanging out the back of the machine? Are they RS232 in which case a vt100 could be used? Was there the concept of a console, or would the machine silently boot? What was needed to boot the machine? Would it boot from hard drive, or was a floppy needed? (I have zero docs and disks for this thing sadly...) Phew! That'll do for now I guess! :*) cheers, Jules

28 years, 3 months

Kaypro problems

by homeline＠ezl.com

> >3) The fuse is fine, but the PSU won't start up. This is suprisingly >common (I've had it twice in the last month). Most small SMPSUs run the >control circuitry off one of the transformer outputs, which leads to a >bootstrap problem (the PSU can't run without the control circuit, but the >control circuit can't work without the PSU running). The solution is a >small circuit to give the control circuit enough power to start. In a lot >of cases this takes the form of a high-value resistor chain from the HT+ >(400V DC) line to the chopper control circuitry. And for some reason this >resistor open-circuits. It's worth checking all high-value resistors on >the primary side. > >When you've inspected the fuse, get back to us and we'll attempt to talk >you through the PSU... > >-tony > > > Well, I checked the fuse on the P/S, and its OK. So what is the next step? Is this something I can take to a repair shop. I know of a TV & stero shop that has worked wonders on an old Pioneer amplifier of mine. A P/S should be of no problem for them. I would like to attemp to fix my self, but I just don't have that sort of time at the moment! Or can anybody recommend someone I can send it (the power supply only) to for repair? Cliff Boyer

28 years, 3 months

question - how to test DMA on peecees right way?

by jfoust＠threedee.com

Tony Duell wrote: >The first requirement is that you're mad. Now that you're foaming blue at the mouth, you could give the speech about how to use the keyboard interface chip to bring the 286 into real mode and back again... :-) - John Jefferson Computer Museum <http://www.threedee.com/jcm>

28 years, 3 months

RETROCOMPUTING LIQUIDATION

by maxeskin＠hotmail.com

When was this thing with "computer literacy in schools is everything" started? I like computers in schools, but I am tired of looking at proposed plans to replace 5 MORE classrooms with computer labs. Is this a classic thing? Would you in general say that computers have affected education (keeping the discussion OnT, of course). > >> snoball wrote: >> > >> > Hi, I am a teacher here at the local elementary school in Humble, TX. To be >> > honest, the computer department here at the school is rather pathetic, two >> > Apple //e's and an XT that was donated that I can't get to work. To be >> > frank, these kids are going into a world where they are illiterate in the >> > basic workings of a computer. I hate to sound desperate, but I have just >> > exausted all leads I know to take on the matter. I saw your ad and thought >> >> Don't panic. Here in New Jersey, the kids are all experts at >> Nintendo (and some of the brighter lights at hacking security), >> but damned few can actually read the manuals. Remember, the >> most important component of "computer literacy" is "literacy". >> If the kids can read, they can learn computers. If they can't, >> there's not much else worth teaching them except to pee on the >> side of the dumpster the cops aren't watching. (I may be a bit >> prejudiced on the side of reading over computers -- I only have >> fifty-odd computers, I've got [half bought new] several thousand >> books, mostly the science fiction I've loved since before the >> "New Math" was introduced to my grade school [after I'd had the >> benefit of learning the stuff that worked].) >> -- >> Ward Griffiths >> They say that politics makes strange bedfellows. >> Of course, the main reason they cuddle up is to screw somebody else. >> Michael Flynn, _Rogue Star_ > > > > ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com

28 years, 3 months

rt-11 programming

by CHUCK92124＠aol.com

i am looking for an RT-11 guru to modify some software for a PDP-11 system running RT-11 V4 year 2000 problem please call chuck@ 619-292-0911

28 years, 3 months

list archives?

by g＠kurico.com

Hi, I just joined this list a couple of weeks ago and it is great. Lot's of great information. I have two quick list related questions. First, is this list being archived somewhere. Just in the two weeks I've been on, it's obvious that there is a huge amount of informational wealth being disseminated. And as any collector of older computers knows, information is the most essential element of collecting (that and software on the proper media). Second, does anyone know of any other lists that focus specifically on collecting? TIA George

28 years, 3 months

Another EBay absurdity

by lgroebe＠insidermarketing.com

>At 10:20 5/13/98 -0500, Russ wrote: >>....I don't see >>anyone paying up to $15000 for a 1977 Apple computer of any model. > >I have personally watched three Apple Ones sell for, respectively, $12,000, >$15,500, and $22,000. The high one was at the Computer Bowl a couple of >years ago, the other two were private collectors, and none was ours (the >one at Fry's). > >__________________________________________ >Kip Crosby engine(a)chac.org > http://www.chac.org/index.html >Computer History Association of California > and there's a hint that one sold for $50K in the Apple docs online at http://www.grin.net/~cturley/USA2WUG/FOUNDING.MEMBERS/HOME.PAGES/STEVE.W/A1 /The%20Index.Page.html can anyone confirm this price?

28 years, 3 months

Interesting c64 usage

by sinasohn＠ricochet.net

Last weekend I was at a garage sale where I spotted a c64 with an interesting job. It was connected to a mixing board to provide automation. That is, the c64 was used to control the functions of the mixer so as to be able to repeast a setup exactly. Pretty neat, and I wouldn't have minded getting it (I've been lusting after 8-bus multichannel mixer for years) but I couldn't justify the $1300 the guy wanted for it. 8^( Came with an interface box, btw, that had the software in it (presumably in ROM) for the automation. --------------------------------------------------------------------- O- Uncle Roger "There is pleasure pure in being mad roger(a)sinasohn.com that none but madmen know." Roger Louis Sinasohn & Associates San Francisco, California http://www.sinasohn.com/

28 years, 3 months

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