Hi Jay, I appreciate you explaining reforming in such detail and I will look it up as you suggest and I'll definitely keep this in mind when I start checking things out in my Altair. Thank you very much.
Kip Koon computer...@sc.rr.com http://www.cocopedia.com/wiki/index.php/Kip_Koon > -----Original Message----- > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Jay jaeger > Sent: Tuesday, July 28, 2015 11:01 PM > To: General Discussion: On-Topic and Off-Topic Posts > Subject: RE: Microsoft multiuser Basic for the Altair 8800 > > 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 <computer...@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 > >computer...@sc.rr.com > >http://www.cocopedia.com/wiki/index.php/Kip_Koon > > > > > >> -----Original Message----- > >> From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Jay > >> Jaeger > >> Sent: Thursday, July 16, 2015 9:39 AM > >> To: cctalk@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 > >> > computer...@sc.rr.com > >> > http://www.cocopedia.com/wiki/index.php/Kip_Koon > >> > > >> > > >> > > >> >> -----Original Message----- > >> >> From: cctalk [mailto:cctalk-boun...@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 <computer...@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:computer...@sc.rr.com> computer...@sc.rr.com > >> >>> > >> >>> <http://www.cocopedia.com/wiki/index.php/Kip_Koon> > >> >>> http://www.cocopedia.com/wiki/index.php/Kip_Koon > >> >>> > >> >>> > >> >>> > >> >>> > >> >>> > >> >>> > >> > > >> > > >
