test-drb February 2009

test-drb@ccmp.vtda.org

196 participants
309 discussions

by chd_1＠nktelco.net

Robert Jarratt wrote: > The harness in my system does not seem to match any of the descriptions I > have seen so far. The wires are not equal in length, but it is not a ribbon > cable with IDC connectors either. The connectors are black rather than > white. The harness wires do not seem discoloured, but I believe that this > particular system may have only had light use in its day. I have a picture > of the harness but I am not sure if the rules of this list allow > attachments. > The key point of your description is that the wires are not equal in length. This COULD be a bad thing. I have a BA23 chassis that had a melted power supply connector. The connectors were AMP MTA .156 IDC connectors with individual wires. The connector housings were Yellow. The failure point was the connection between the harness and the power supply pin. As Allison describes, the problem is that there was an unequal distribution of current between shared pins. I replaced the harness with one that I made myself using high current box connection pins... with equal length wires. There is a field service notice that describes the problem and even mentions the color of the connectors. I remember reading it and saying to myself that was my chassis. I just can't remember where... -chuck

15 years, 9 months

AAARRGGGHHHH ... people still stealing my work

by evan＠snarc.net

>>> Else something more wordy and crafted in legalese, rather than a plea. I hate legalese. I was trying to be nice. :)

15 years, 9 months

Advice for Tek 4051 vector-drawing issue?

by derschjo＠mail.msu.edu

Inherited a Tektronix 4051 this afternoon (really, really cool old machine - 6800 CPU, vector storage-tube display) and after cleaning it out and reseating the socketed chips it appears to work almost correctly. (Even the tape drive works after cleaning the head... amazed that the pinch roller hasn't turned to goo.) The one issue is that "long" vectors do not get drawn as straight lines -- they end up curving in the direction of the destination. I've taken a photo to demonstrate: http://yahozna.dyndns.org/computers/tek4051/unvector.jpg The above is _supposed_ to be drawing a line from 0,0 to 100,100 and back, but as you can see, it's not really doing a very good job. Short vectors seem to draw OK, as do perfectly vertical and horizontal ones. Text gets drawn fine. I have the schematics but I've never dealt with a vector-based display before (only other vector display I have is in my Vectrex, and I haven't had to tweak that one yet.) Any ideas where to start? I figure the D/A converters on the CPU board are working correctly since text positioning works, and the endpoints of the vectors seem to be correct. Bitsavers has the schematics at: http://www.bitsavers.org/pdf/tektronix/405x/070-2286-00_4051_Service_Vol2_M…, (see page 92 for the start of the display schematics.) And a higher-level overview of the functionality at: http://www.bitsavers.org/pdf/tektronix/405x/070-2065-00_4051_Service_Vol1_M… (See page 147 for the start of the display overview.) Thanks! Josh

15 years, 9 months

Powering up a 20-year old MicroVAX II

by ard＠p850ug1.demon.co.uk

> > > *Rob, possibly you made the 110/240 switch wrong, but also possible is > > that the PSU just wasn't ready to be turned on like that. > > Electrolytic > > Capacitors (of which there are many in that PSU) tend towards > > non-functionality the longer they sit unused. Without those caps > > working right, the PSU will do pops, smokes, and other alarming things. > > Then good luck fixing it. > > Do you mean that it will be difficult to fix, even if I can find someone who > really knows what they are doing? It might be. It depends on just what's failed. In SMPSUs (Switch Mode Power SUpply Units), one component failure can wreck other components too (ecven to the extent of multing PCB tracks) and if you don't find _all_ the failed partsm, but juet replace some of them and turn it on again the same thing can happen again. > > > > > What I do with an old PSU like that is test each cap prior to it ever > > being powered up.. both for capacitance and ESR. Usually, some or all > > of the caps need reforming or even replacement. Only after the caps > > are back to health, do I then give the PSU power... at first with the > > smallest load I can get away with. > > I only have a basic multimeter so I don't know if I would have had the > necessary equipment to do this, do you have any advice on the minimum > equipment needed? Now that there has been some damage is it sensible to You need a multimeter, certainly. An ESR meter is very useful too (this measured the effective series resistance of a capacitor, basically the higher the value the worse the capacitor is). A good 'scope is handy, and if you want to owrk on the primary side of the PSU when it's running, or examine waveforms there, you need a mains isolating transformer. And the 'series light ulb' (a mains-rated lightbulf, or 2 in series, conencted in series with the DC supply to the chopper circuit to limit the current in the event of a catastrophic failure) will save your nerves and possibly some expensive components [1]. But very important is a _brain_ :-) [1] THe fact that mains-rated light bulbs are getting hard to get thanks to the governemnt does not help here! > replace the blown capacitors and any other ones that don't measure well? > > > > > If it's a switcher PSU (as that one is), I'll bring it up quickly to > > about 90V using a variac... then in 5V increments every 1/2 hr after > > that to 130V, then back down to 120V. This in the USA. > > I looked up variacs but there seem to be an awful lot of different ones, > again any recommendation as to the minimum I would need? I would recomend against using a Variac on an SMPSU unless yoy really know what tyou are doing. An SMPSU is a fairly good aproximation to a contant _power_ load, in other word the input current increases as the input voltage decreases. Some SMPSUs can actually be damaged by running them at too low an input voltage, while plenty of other types do strange things. > By the way, I am aware that PSUs can be very dangerous to meddle with when > you have limited knowledge. How long should I leave the PSU between any Indeed. Mains, and the rectified mains you find in SMPSUs, is probably the most danagerous voltage you're going to come across. > tests to allow the capacitors to discharge? The label on the PSU says to > leave it 5 minutes, I suspect it should be longer. It's impossible to say. A good electrolytic capacitor with nothing connected to it will hold the charge for quite a time. Of course when the supply is working, the chopper circuit tends to discharge the mains smoothing capacitors, so the charge won't remain for very long. And many supplies have bleeder resistors (resistors connected in parallel with the mains smoothing capacitors) to discharge them. But of course those could fail too. What I do is open up the supply carefully and then measure the voltage across the mains smoothing capacitors (sometiems, as in the case of the HP9845 and DEC PDP11/44 supplies there are clear testpoints to do this). If it's more htan a few volts, I carefully connect a suitable resistor (a few 10's of kilohms) across the capacitors to discharge them. -tony

15 years, 9 months

Advice for Tek 4051 vector-drawing issue?

by aek＠bitsavers.org

> I'm looking into whether if it's possible to adapt one of the "backpack" > expansions to take EPROMs instead of MCM6832 ROMs. Later modules used EPROMs. I've put everything I had dumped up under http://bitsavers.org/bits/Tektronix/405x along with scans of the binary loader and real time clock pcbs.

15 years, 9 months

GPIB cards [WAS: Re: Advice for Tek 4051 vector-drawing issue?]

by devonstopps＠gmail.com

Speaking of GPIB cards, if anyone needs an ISA GPIB interface card, let me know. They're usually NI AT-GPIB/TNT+ cards. We usually toss a few every couple of months. For the cost of shipping (about $15CAD to almost anywhere). Also have Sun Ultra10 and Ultra5 free for pickup in Kingston, ON. On Sun, 22 Feb 2009, Josh Dersch wrote: > > Richard wrote: >> >> I guess the best way to get data transferred from these systems is to >> >> use the GPIB interface and transfer the programs out of the system and >> >> into the internet. I wonder if the easiest would be to use a >> >> Commodore GPIB compatable floppy drive or something.

15 years, 9 months

Can someone help me identify this IBM machine?

by aek＠bitsavers.org

> So the other pictures in that bunch implies that most (all?) of the > stuff formerly at the museum is now at the offsite warehouse? The space which was formerly large and small storage in Mountain View has been packed and moved offsite to make room for an exhibit which is in development that will take up much of the first floor. This also helped the efforts to get the collection cataloged. Exhibits in the front of house are still there.

15 years, 9 months

Randy Cook, TRSDOS, and Datapoint

by aek＠bitsavers.org

> Can anybody here compare the two and find threads of similarity? Gordon P. seems like the guy to ask..

15 years, 9 months

8088 vs. 80c88

by les＠frii.com

I just thought of another intersting example. The version of adventure I used to play (550 point Geotz B01) behaved differently on a Z80 and a 8080. Something happened at the beginning of the game on a Z80 (It asked for your name, or have a version message, or something) which did not happen on an 8080/85. With that exception, it worked fine on either processor. That allways struck me as odd, and became my test for what processor was in a system. Les

15 years, 9 months

Can someone help me identify this IBM machine?

by aek＠bitsavers.org

> Where is this thing? Do you know if there is any more of it left? At CHM. Apparently one of our volunteers went into storage while the artifacts were still in Mtn View and got creative with his camera. The 610 console was all that was donated.

15 years, 9 months

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test-drb February 2009