test-drb July 2000

test-drb@ccmp.vtda.org

155 participants
521 discussions

by mrbill＠mrbill.net

I've got a chance to pick up one of these for $10 at a local junk shop; however, this one is BROWN - I thought they were all shades of BLUE! (or am I incorrect)? Should I even bother picking it up and hauling it out to the truck? Bill -- +-------------------\ /-----------------+ | Bill Bradford | www.sunhelp.org | | mrbill(a)mrbill.net | www.decvax.org | | Austin, Texas USA | www.pdp11.org | +-------------------/ \-----------------+

25 years, 1 month

Using WD40 on a Remote Services Consoles

by agraham＠ccat.co.uk

Eric wrote: > Due to some idiot attempting to make their automobile occupy the same > space-time coordinates as mine, a bunch of chinese food was spilled on > my copy of the manual. Assuming that it's still legible, I'll try to > write up a summary when I find some time. *lol* - what a great description of a crash. Hope you weren't injured though! One of these days I'll get round to having another look at my Apple ///'s keyboard which was smashed in a similar incident. a

25 years, 1 month

Shoddy UPS service

by fauradon＠mn.mediaone.net

>Now you know why UPS is called Untied Parcel Service. I thought it was United Partial Service Francois

25 years, 1 month

Weekly finds

by dhquebbeman＠theestopinalgroup.com

> A LOAD of printer ribbons, boxes of a dozen, single ribbons, too many to > sort just yet. I may just take a couple pictures and put the mess on my web > site. DEC, QUME, Epson, NEC, a bunch, most nicely still sealed in bags. I'd be interested in some DECwriter-III (LA120) ribbons... these are the ones that look like big typewriter ribbons, just a pair of plastic reels with inked ribbon, if you have any in that batch... regardsm -doug quebbeman

25 years, 1 month

Switching PSU Theory of Operation / Repair Tips & Techniques

by dhquebbeman＠theestopinalgroup.com

> On Wed, 26 Jul 2000 22:21:47 +0100 (BST) Tony Duell <ard(a)p850ug1.demon.co.uk> wrote: > > > The electrolytics are Mallory CGS 2900MFD 250VDC. The one on the - side > > > > And there's another clue. Those capacitors are rated for 250V, and yet > > you're seeing 280V across them. While they'd probably stand that for a > > short time, not computer power supply would be designed to work like > > that. So either there's a fault, or you're not measuring the voltage you > > think you're measuring. > > I think Tony's spotted a very strong clue, here. Kinda > makes me suspect that the voltage measurement is going > wrong for some reason. Could there be some non-DC > component that's making the meter read wrongly? With the PSU disassembled, and the secondary out of the way, I'm going to take fresh reading on the primary today at lunch. I'll post the results when I get back to the orifice, er, office. -dq

25 years, 1 month

Switching PSU Theory of Operation / Repair Tips & Tech niques

by dhquebbeman＠theestopinalgroup.com

> Hi > I'm still puzzled over the 600V reading. My guess > is that there is a problem in the meter. As far as I know, > the inputs are usualy configured as a doubler when used > with 115V and a bridge when used for 220V. I don't > recall the circuit but I remember it was a clever trick > in that one could change it with a single jumper. I wish my Fluke was working (the LCD has gone black). I dropped my RatShack analog meter a few days back, and the needle sticks in spots, but a tap on the meter face usually frees it up. However, it measures 115v AC correctly. But, I'm going home at lunch to make a few more careful measurements of the PSU primary (the PSU is disassembled now, and I've unsoldered some parts out of the secondary PCB to test them, so we won't have any of that confusing the issue). > What a BBU? I'm assuming it's a battery backup unit. -dq

25 years, 1 month

Switching PSU Theory of Operation / Repair Tips & Techniques

by dhquebbeman＠theestopinalgroup.com

Good Morning, All! In his last reply, Tony Duell stated (somewhere in all those quotes): > > You may not have yet seen the correction I posted, but I was seeing that > > only when I measured the + terminal of one of the blue electrolytics, and > > the - terminal of the other. Why would I do that? I'd just gotten out of > > Yes, but aren't the 2 capactiors in series, something like : > > ------------+-------------------- +ve > | > ===== > ----- > | > ------------+ > | > ===== > ----- > | > ------------+--------------------- -ve Yes. I've made a schematic of this portion of the circuit. And while I'm not very good at ASCII art, I've made a stab at it, as you can see below. > And you're seeing 600V between the 2 points I've marked '+ve' and '-ve', > right? That's still twice what I'd have expected -- I'd expect peak mains > voltage (i.e. 115*sqrt(2)) across each capacitor, or about 320V between > +ve and -ve in that diagram. > > I am still puzzled as to how it gets 600V without either other large > capacitors, or a mains-frequency transformer. If we have a 300vdc source, positive with respect to ground, and we have a 300vdc source, negative with respect to ground, don't we have a 600vdc potential between the two sources (as long as they share a common ground)??? > I will just ask again -- this thing does run off 115V, right? Yup. Now, let's talk failed components. And I suppose I'll take a stab at ASCII art by adding to what you've already "drawn": --------------------- + to BBU | | +---------{ MCI 307138 }---------------+-------------------- +ve / \ | + | / \ ===== / 12k ohm / \ ----- \ 5% / \ | - / ----* *---------------------------------+----------* | \ /| | + \ | \ / | ===== / 12k ohm | \ / | ----- \ 5% | \ / | | - | | ----------{ MCI 307138 }---------------+--------------------- -ve | | | | | | | | ---------------------- - to BBU | | | | | | 115v Load 115v Neutral In the diagram above, 'BBU' is the label on a connector to which the labeled lines run. I think it's for a Battery Backup Unit. Cool, who needs a UPS when you've got a bank of kick-ass batteries? But I digress... The components that I've shown as {MCI 307138} are what appear to be either large disk ceramic caps, or, judging by appearance, more likely MOVs. The one on the + side is discolored and cracked open along its circumferential periphery. It was blue, some of it turned green, most of it turned black. The one on the - side is discolored similarly but it not cracked open. These components are on a small board which is separate from the main PCB and which mounts by being screwed onto the tops of the two electrolytic caps. The electrolytics are Mallory CGS 2900MFD 250VDC. The one on the - side was in close proximity to a power resistor on the main PCB. The power resistor on the main PCB was a Dale 15K ohm 5% 20W unit. One leg of the power resistor is soldered to a trace which leads to what I think it the oscillator, which is one of two separate boards that plug into the main PCB. The power resistor has changed in value from 15k ohms to infinite ohms. The main PCB was discolored underneath the power resistor. The electrolytic shown above on the negative side which was in close proximity to this power resistor may have suffered some damage, as the blue plastic (heat shrink?) that Mallory uses for the CGS caps is discolored where it was in closest proximity to the power resistor. There are some other components, quite far away on the PCB from the area I've been discussing, that have also gotten hot enough to badly discolor the PCB. These components include some small 5% power resistors, two other items that look like resistors but may not be (as the color banding looks odd), and a couple of polystyrene caps. I unsoldered one of the little 5% power resistors (four of these, with little ceramic spacers/insulators on the leads, 51 ohms). It tested OK. These power resistors are nearby to two transistors (in what I think are TO-3 cases, the ones that kinda look like hats when viewed on-edge). Also, in that area of the PCB, the leads to one of the transformers have heated up and discolored the PCB underneath. A couple of other notes: The yellow AC LED appears to be lit from a signal that comes from a circuit on the main PCB that monitors the line voltage. Unfortunately, said circuit requires the DC supplies that aren't currently working. > > > > complex looking boards (although they're only 2-layer) with custom PALs and > > > > the like. > > > > > > PALs? Are you sure? It's not at all common to have significant amount of > > > digital electronics in an SMPSU. Most of the time it's either simple > > > analogue circuitry either as discrete components, or one of the well-know > > > SMPUS control chips. > > > > These look like digital boards to me. I'll pull 'em and either scan them > > Well, you've seen it, so I guess you're right. Seems a little unusual, though. > > > or take a digital photo, as well as record a few part numbers. > > If you could post the numbers on any ICs on the boards, I can see if they > make any sense. Or have they used house-numbers only ?:-( The daughter board containing the PAL has a 16L2A, IIRC. A TI part. I was told that the PSU provides a signal to the Virtual Control Panel board called "Confidence", which is like the PowerGood signal that PC switchers put out. This daughterboard may monitor the voltages and then provide that signal. That concludes my investigation to date. I'm starting to feel good about the possibility of repairing this PSU, even without the test equipment I should normally have. By replacing the obviously failed components along with the ones you and others will hopefully suggest should be replaced due to the failure of the obviously bad ones, I think this thing may damned well work again. > > > > If it matters, the room in which I keep the Prime was hotter than > > > > I usually let it get when I have the Prime running (I don't have > > > > central A/C, so I have a window unit in an adjacent bedroom and > > > > > > In which case look for dried-up (high ESR) electrolytic capacitors. This > > > is a very common heat-related problem. > > > > Would I not have to open them to make that determination? I though they > > contained PCBs or somesuch toxic chemical. > > Firstly, no, don't take the capacitors apart -- you'll ruin them if you > do. I assumed that... and I don't want to be out the US$45 a replacement would cost, but... > Measure the ESR electically -- either with a special ESR meter (the > Dick Smith Electronics one is claimed to be very good and not expensive), > or on an impedance meter. I've never used the Dick Smith meter -- I was > going to buy one and then I was given a rather nice digital impedance > meter (it applies a sine wave to the device-under-test, measures the > inphase and quadrature componentes of the current through it, and > calculates the resistance and capacitance/inductance). But I've heard > nothing but good things about said ESR meter. ...I figure the test equipment will cost more than the replacement parts. Of course, the test equipment has value beyond this one problem. :-) > Secondly, the electrolyte in these capacitors is not PCB-based (PCBs are > not electrolytes anyway...). The electrolyte is not particularly harmful. > Actually, according to somebody who works with _large_ transformers and > capacitors, yes, PCBs are dangerous _in quantity_, but unless you're > really silly, the amount in one capacitor, or even all the capacitors in > an HV PSU, is unlikely to do you any harm. I can't really comment on this > -- it's not my field. What, you mean this isn't the Classic Chemistry list? 8D Hey, I feel like we're making progress. Tony, thanks again, and to everyone, I kept this on the list rather than take it private because it just seems like someone else might benefit from it, and of course, I'm seeking input from all who'd care to contribute. regards to all, -doug quebbeman

25 years, 1 month

Announcing... Rent a wreck

by agraham＠ccat.co.uk

Grrrrr......sassenfrassenworkinglisa2 :) > 47 Apple Lisa 2 > 48. Apple Lisa 2 a

25 years, 1 month

Apple IIGS for parts

by agraham＠ccat.co.uk

There's a question! Which drives did the GS use - bog standard disk ][s? My GS is unused ATM since it's diskless. -----Original Message----- From: Marion.Bates(a)dartmouth.edu [mailto:Marion.Bates@dartmouth.edu] Sent: 26 July 2000 18:41 To: classiccmp(a)classiccmp.org Subject: Apple IIGS for parts Heya, First off, I apologize for sending this again -- I am losing track of what I write and who I send it to. I think I offered the drive but not the computer last time. Whatever... I have a IIGS here with a logic board problem (the "sound interrupt" issue I mentioned a week or so ago) and a bad power supply to go with it which looks and smells fine but nothing happens when you flip the switch. And yes, I checked the fuse. Got a helluva shock from one of the caps too. :-/ Anyone want these items for cost of shipping? Let me know off-list. There's even a bad 5.25 Apple floppy drive to go with it! Spins up but won't read. Thanks, -- MB

25 years, 1 month

Back to the A1097C monitor again

by agraham＠ccat.co.uk

> actually a Sony GDM1960 (or near equivalent), and those were made in > various OEM versions for HP, Sun, Dec and possibly SGI, > differing mainly in The A1097C is a later monitor - you're thinking of the DEC VRT19 (GDM1961) that I was also considering using on the PC. > > or > > do I get nowt until my GeForce has been fully initialised > at 1280x1024? > > Yup :-) Oh well. I don't think I'll bother then, unless I get some sort of cheap monitor switch box...... cheers!

25 years, 1 month

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test-drb July 2000