test-drb August 2015

test-drb@ccmp.vtda.org

206 participants
257 discussions

by shadoooo＠gmail.com

Hello Adrian, how are you? Maybe you still have the SDI disks aside for me? Any time to ship them to me? Thanks in advance! Andrea

8 years, 8 months

diagnosing an Intel Series II MDS monitor failure

by cube1＠charter.net

Sounds just like the supply on my Altos. What a pain. Eric Smith <spacewar at gmail.com> wrote: >I previously wrote about the monitor of my Intel Series II MDS going >out, which was because the +15V DC supply tripped the crowbar. The >voltage adjust was all the way to the minimum, and the voltage was >still about 17.4V with no load, and trips the crowbar with even a >small load. I think someone previously encountered this problem and >adjusted the pot rather than fixing it, and the problem has gotten >worse since. > >The root cause of the failure appears to be that the internal voltage >reference of the uA723, which is specified as 7.15V ?0.35V, is now >9.4V. The uA723 needs to be replaced. The uA723 is still readily >available, but due to the construction of the power supply, replacing >it is relatively difficult. Just probing the pins of the chip was a >challenge. The pass transistors are mounted to 1/8 inch aluminum >plate, but the pins are soldered into rivets in the single-sided PCB, >entering from the etch side (which is closest to the aluminum), so >they will have to be desoldered to get at the etch side to replace the >723. I considered just cutting the pins of the 723 and soldering >another (or a socket) onto it from the component side, but pins 1-7 of >the 723 are right next to a big axial electrolytic so there's no way I >can solder that side. Input and output wires to the board are soldered >into single-pin cup thingies on two opposite edges of the board, so I >can't even get the board into an orientation suitable for working on >it without desoldering or cutting some of the wires. > >I haven't bench-tested the monitor, because I haven't kludged up a >suitable signal source yet, but I don't think there's anything wrong >with it.

8 years, 8 months

Reforming capacitors (technical description, not politics)

by spacewar＠gmail.com

Some people seem to think that "reforming" an aluminum electrolytic capacitor is some kind of cheat, akin to zapping NiCd cells or rejuvenating CRTs. Actually reforming is the same electrochemical process that the manufacturer uses to "form" the capacitor in the first place, building up the aluminum oxide layer, before the sheet is rolled into cylindrical form. The manufacturer typically uses a forming voltage higher than the rated voltage, from 135% to 200%, to provide margin for shelf life. When the capacitor goes unused for an extended time (shelf life), the oxide layer gradually breaks down, increasing the capacitor's leakage current and reducing the effective usable voltage of the capacitor, which is proportional to the minimum oxide thickness. If the oxide has developed spots that are too thin for the applied voltage, it may be damaged ("punch-through") when that voltage is applied. Punch-through tends to be a runaway process, so even a small amount of punch-through usually completely ruins the capacitor. Reforming the capacitor by applying current-limited power rebuilds the oxide layer to prevent this type of damage, and to reduce the leakage current back to within the specifications. The current limiting is what prevents the reformation process from causing punch-through and damaging the capacitor. Many of the capacitor vendors actually publish recommendations for reforming their capacitors. See for example information on manufacture on pages 13-14 and a brief recommendation of reforming procedure on page of 17 of Kemet publication F3304 dated June 2009: http://www.kemet.com/ProductCatalog%20Documents/F3304.pdf Also pages 2-4 on manufacture and page 16 on "recondition" (reform) of "CDE Aluminum Electrolytic Capacitor Application Guide": http://www.cde.com/resources/catalogs/AEappGUIDE.pdf Also pages 1-5 of Nichicon "General Description of Aluminum Electrolytic Capacitors": http://www.nichicon.co.jp/english/products/pdf/aluminum.pdf In at least some aluminum electrolytic capacitor manufacturing processes, there is actually a reforming step done after assembly, in addition to the initial forming. See page 9 of the Panasonic "Aluminum Electrolytic Capacitors Technical Guide", dated April 2013: http://industrial.panasonic.com/lecs/jp/i/29880/TAL_E/TAL_E.pdf The reforming process WILL NOT fix other things that may go wrong with the capacitor, such as failed seals allowing the electrolyte to dry out, or corrosion, or punch through which can result if the oxide layer is degraded and voltage is applied without current-limiting. The US DoD published a technical handbook detailing their policies and procedures for reforming aluminum electrolytic capacitors that sit in inventory for years, MIL-HDBK-1131. As of 1999 this is "for guidance only and should not be cited as a requirement, but the information in the handbook may be useful in determining or evaluating requirements." For non-mil-spec capacitors, it recommends inspection and possible reformation every 3-6 years of shelf storage. It recommends disposal after 12 years of shelf storage, but AFAICT they're just being conservative, possibly due in part to not having enough practical experience with reforming very old capacitors. Shelf storage is of course equivalent to having the capacitor in-circuit but unpowered. Having the capacitor powered in circuit for any significant length of time will reform the oxide to some extent based on the applied voltage, though not up to original factory spec. When I reform capacitors myself, I use a reforming voltage of 135% of the rated voltage. Since I use a suitably low current limit, this has no significant probability of damaging the capacitor, but as with the initial factory forming, provides some margin for further shelf life. In my experience, aluminum electrolytic capacitors in equipment that has been unpowered for 30 years or more almost always need reformation, but they almost always meet factory specs (capacitance, ESR, and leakage at rated voltage) after reformation. Since I don't tend to restore equipment newer than that, I don't have any empirical data on how much shelf life they can have without needing reformation. I'm not particularly advocating for or against reformation, as compared to replacement. Anyone restoring equipment with electrolytic capacitors is advised to to read the references and decide for themselves. Eric

8 years, 8 months

RM 380Z Special Control Unit (?)

by cube1＠charter.net

SOME of the later S100 systems had regulated supplies and then ditched the board regulators, usually leaving a place to put a regulator with just a jumper wire in place of the regulator. tony duell <ard at p850ug1.demon.co.uk> wrote: >> > >> > ... Which also may well not be RML original. The 380Z has a regulated PSU, >> > S100 has separate regulators on each board and an unregulated PSU. >> >> Indeed, although I do recall a heatsink mounted externally on the back of >> the chassis (where the fan would be on the later hardware) with the early >> machines - I just don't know details of the internal PSU. > >I was going to say that that heatsink didn't look original, but fortunately I >kept my mouth shut and didn't insert my foot :-) > >I've only seen the later black 380Z's with built-in 5.25" drives, first at school >and now the one I own. On those the PSU is entirely internal, it's a little >chassis that fits round the mains transformer and carries a PCB of >recctifiers, regulators, etc. For some odd reason the schematic of that is not >in the manual, I guess I should draw it out sometime. It's not complicated. > >Thinking about it, I do wonder what that heatsink/regulator is doing in an S100 >system. Most likely it is the original RML supply and somebody has connected >to the unregulated inputs to its regulators > >-tony >

8 years, 8 months

RM 380Z Special Control Unit (?)

by robert.jarratt＠ntlworld.com

I remember the Research Machines 380Z and wouldn't mind getting one should the opportunity arise. But I have no recollection of a "Special Control Unit", so does anyone know what this is? http://www.ebay.co.uk/itm/Faulty-Vintage-Research-Machines-380Z-Special-Cont rol-Unit-Computer-/331617471655? Some kind of peripheral maybe? Regards Rob

8 years, 8 months

Equipment available (Wichita, Ks)

by microfilm＠microfilm.kscoxmail.com

Still cleaning the shop, trying to be out by the end of the week-ish. We have the following equipment available: TU-80 family tape drive, in frame. Works, passes diagnostics. Make offer. Photos: http://microfilmks.com/LMSI/ Unknown power supply module. Has NCR part numbers but google gives no love. +5 (x2), -5, +12, -12. Make offer. Photos: http://microfilmks.com/Ebay/UnknownPSU1.jpg and UnknownPSU2.jpg Discom electron tube, PN 123788-2. These came out of COM microfiche cameras, and have a blue display. Not sure how to go about shipping them securely, but if you're interested, we can figure it out. I have several of these. DEC SHD1Z-ZZ SCSI drive cabinet, tower configuration. Has SCSI-2 personality module, power supply, SCSI terminator and cable, 6 drive trays for 50-pin drives. Also has 4 spare drive trays and one spare power supply. Includes 6 1.2G SCSI drives, or if you prefer, I can remove them to lower the shipping weight. Asking $50 obo. All shipping is from Wichita, Ks, 67213 --Shaun

8 years, 8 months

accidental post allowance

by jwest＠classiccmp.org

drlegendre wrote: ---- How did his last missive make it through to the list in the first place? Didn't Jay just recently say he was perma-banned? ---- Within moments after I posted that he was banned, I went to the mailman interface, and his account was not in the membership list. I assumed he had unsubscribed himself shortly after his first post. When I saw his next (and last post), I dug further. His email was on a "whitelist" along with all members of cctech. This was a vestige of how the old "two lists joined at the hip" was configured. So I had to manually remove him from the whitelist, even though he wasn't subscribed. My Apologies for the oversight, but I believe it is fixed now. Be advised that there is always a chance he's still subscribed under some other unknown/non-descript email address. I'll weed them out as they are discovered. J

8 years, 8 months

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test-drb August 2015