Microsoft multiuser Basic for the Altair 8800

Jay jaeger cube1 at charter.net
Tue Jul 28 22:01:07 CDT 2015 

OK at the risk of restarting a long discussion about the value of reforming or lack thereof....

Reforming a cap means to apply power to the cap at or a little below its rated voltage but limiting the current with a resistor in series with the cap until the voltage drop across the resistor indicates acceptably low leakage current.  At the low voltages in use on an Altair I typically use something in the range of 4.7k ohms.  I have a dual 1-20v power supply to do this.

The idea is that this redeposits some of the aluminum that had migrated into the electrolyte while the cap was idle reducing the leakage current of the capacitor.

This procedure  done correctly with the correct polariy and voltage will never harm the cap, so it isn't unreasonable to reform all of the filter caps on a linear supply like that on an Altair 8800. The current list!meeting resistor prevents the cap frm drawing too much current and overheating or worse until the reforming is complete or too much time has elapsed without reaching an acceptably low leakage current.

Just google it and you will find articles on the procedures.

As others have pointed out, this will not help if the cap has unacceptably large effective series resistance (ESR).  On a linear supply, That will show up as unacceptably high ripple ac on top of the DC the supply is designed to provide.

I would test the supply with at least SOME test 
Load before using it to supply the machine.

When I did this to my Altair a few years back I think rather than disassembling the power supply to unsolder the caps I clipped one lead of each one so that one lead was free, but that then leaves one with the need to splice them back, but does avoid potential damage to the board.  I also recently did that with an ALTOS which has switching supplies.  Both would probably have done just fine without reforming.  I also did in on an IMSAI, same story.  I also did it to a pdp12, which had blown out rectifier before I did this.

Doing a good job of restoring a machine does often mean disassembling and reassembling.  It comes with the territory.

It sounds like you !might have pretty limited electronics experience, and if that is the case you might try and find 
Someone local to help you over the humps.

SAFETY FIRST.


Kip Koon <computerdoc at sc.rr.com> wrote:

>Hi Jay,
>Thank you so much for the advice.  What is reforming a capacitor?  Does that mention the electrolytic capacitors may have to be repolarized?  If so, how to you do that?  How do you know if a power cap needs to be reformed or not?  To get to the transformer, I'll have to take out just about everything including the card guides.  Labeling the wires will be paramount too.  I don't want to get those rascals mixed up!  If remember my linear power supplies correctly, I don't need to put a load on them when I test them, but I will need to test the caps disconnected, correct?  I doesn't sound too difficult, just tedious and much detail to consider.  I definitely want to baby this thing.  :)  Thanks again for the restoration advice.  I'll need it and more before I'm finished.  Take care my friend.
>
>Kip Koon
>computerdoc at sc.rr.com
>http://www.cocopedia.com/wiki/index.php/Kip_Koon
>
>
>> -----Original Message-----
>> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Jay Jaeger
>> Sent: Thursday, July 16, 2015 9:39 AM
>> To: cctalk at classiccmp.org
>> Subject: Re: Microsoft multiuser Basic for the Altair 8800
>> 
>> First of all, safety first when working around these power supplies.
>> You have mains voltage exposed all over the place, including the front panel switch.
>> 
>> What I typically do is take it all the boards out and disconnect the power supply, and pull it out.  I then re-form the capacitors by
>> taking them off completely or, more often, unsoldering one lead.  In one case recently the power supply was regulated (an Altos
>> computer), and the power transistors were inserted through the power supply case and into the board from the backside, making
>> removal both a pain and a little risky, so I just clipped one lead of each larger in place to do the re-forming (it turned out that in that
>> particular case, they really didn't need it).  I'd be pretty surprised if you actually had to replace your capacitors.  For reforming I have
>> had pretty good luck with a 4.7K ohm resistor in serial with the capacitor, and in more than half the cases, the capacitors really didn't
>> need it.
>> 
>> The transformer is either good or not - and it is probably just fine.
>> Just measure its output voltages.  Do make sure that the transformer is wired for your voltage depending upon where you live.  One
>> could disconnect it first, but the odds of it putting out too high a voltage are very very slim, so long as it is wired for the mains voltage
>> wherever you happen to live.  Bad ones either put out nothing for one of the voltages (open winding) or get hot (shorted winding).
>> Neither is dangerous to the rest of the power supply.
>> 
>> Then, check all the voltages to make sure they are not way too high, and throw and oscilloscope on it to make sure that there isn't a
>> whole lot
>> of ripple (typically caused by a bad rectifier).   Remember that on the
>> original Altair and most S100 machines each board had its own regulator, so this isn't an exact thing.  (On my machine, I actually had
>> to add a second 8V supply in order to provide power for a backplane completely full of boards.)
>> 
>> For bootstraps, perhaps look for a ROM board on eBay (a Bytesaver or the like), and burn yourself a ROM.
>> 
>> For a serial card, you can find T-UART or IMSAI MIO and the like show up
>> on eBay pretty frequently.  Be patient so you don't overpay. ;)   Real
>> MITS Altair cards come up far less frequently.  Make sure you research (say, on bitsavers.org/pdf) which ones support current loop if
>> you really want to hook up a real teletype.
>> 
>> Not sure where you'd find your multi-user basic, but there is quite a lot of Altair/S100 software available as part of the SimH
>> environment, and a separate web site at http://schorn.ch/altair_6.php
>> 
>> JRJ
>> 
>> On 7/15/2015 1:56 PM, Kip Koon wrote:
>> > Hi Drlegendre,
>> > How did you go about checking things out before you applied power for the first time (again)?  :)  I think I need to check out the
>> electrolytic capacitors and the transformer at least.
>> > In my system, the front panel is wired to the backplane along with the power supply wires so when I do power up, how do I protect
>> everything?
>> > There are screws the power wires come from, but they are difficult to get to.  Do I need to consider replacing any other caps?
>> > Do you have a write up about your experience?  Any help you can give in the hardware department is most appreciated.  Thanks in
>> advance.  Take care my friend.
>> >
>> > Kip Koon
>> > computerdoc at sc.rr.com
>> > http://www.cocopedia.com/wiki/index.php/Kip_Koon
>> >
>> >
>> >
>> >> -----Original Message-----
>> >> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of drlegendre .
>> >> Sent: Wednesday, July 15, 2015 1:15 AM
>> >> To: General Discussion: On-Topic and Off-Topic Posts
>> >> Subject: Re: Microsoft multiuser Basic for the Altair 8800
>> >>
>> >> Hey Kip
>> >>
>> >> I can't help you with the software, but I just finished an Altair
>> >> restoration (my first) a few months ago, and am still interested in
>> >> getting the machine connected and actually doing something
>> >> interesting. The Altair was almost totally below the radar by the time I really started getting up to speed on micros, which would
>> have been around 1983-1984 or so. This one was sort-of given to me by a former colleague of mine, around eight years ago. It was a
>> total basket case, a real pile.. but it seems to be sorted at this point.
>> >>
>> >> It would be great if you'd let me follow along, keep in touch and let
>> >> me know how you're working to get the Altair linked up to the term,
>> >> getting the system bootstrapped, loading software, etc.. that's been a problem here, figuring out the serial I card (or finding one to
>> replace it, that does have docs).
>> >>
>> >> Best,
>> >> Bill
>> >>
>> >> On Tue, Jul 14, 2015 at 11:56 PM, Kip Koon <computerdoc at sc.rr.com> wrote:
>> >>
>> >>> Hi Guys,
>> >>>
>> >>> I have finally decided to restore my original Altair 8800 which has
>> >>> been in storage for over 30 years.  Does anyone have a copy of
>> >>> Microsoft's Multiuser Disk Extended Basic for the Altair 8800?  When
>> >>> I was in college in '79 to '81, in the computer room was an ASR-33
>> >>> Teletype and 3 Learseigler terminals connected to an Altair 8800B.
>> >>> An IMSAI was also there connected to one
>> >>> ASR-33 Teletype.  I'd like to resurrect this multiuser Basic
>> >>> software environment on my Altair someday once the restoration is complete.
>> >>> Any help in securing a copy of all the necessary software would be
>> >>> most appreciated.
>> >>> Thanks a bunch in advance.  Take care my friends.
>> >>>
>> >>>
>> >>>
>> >>> Kip Koon
>> >>>
>> >>>  <mailto:computerdoc at sc.rr.com> computerdoc at sc.rr.com
>> >>>
>> >>>  <http://www.cocopedia.com/wiki/index.php/Kip_Koon>
>> >>> http://www.cocopedia.com/wiki/index.php/Kip_Koon
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >
>> >
>

More information about the cctalk mailing list