test-drb October 2001

test-drb@ccmp.vtda.org

259 participants
770 discussions

by acme_ent＠bellsouth.net

> > Since "they never did provide BASIC" then there was *always* "no ROM > > BASIC." That's like stopping the machine with a message stating "no > > printer." Why not display something understandable to a common user, such > > as "no bootable device?" > > Because INT 18h doesn't check for bootable devices. It is the entry to > ROM BASIC. It may well be that the most common time that it is called is > from the bootstrap after both floppy and hard disk boots have failed, but > that doesn't mean it's the only time it can be called. Tony, are you simply being obstinate here, or didn't you see the above reference to "common user?" Do you think "common users" -- not to be disrespectful to plain old computer users -- read BIOS listings??? What I mean to say is: Suzy Six-pack, who ekes out a living typing up MS Word documents, doesn't know shit about the internals of the machine she uses. > Actually, one thing that really annoys me are error messages that don't > describe the real problem, but only the most likely cause. I need to know > waht's really going on so that I can fix it. Odd, that.... Yes, and even more odd is that you fail to see that "no bootable device" at power-up actually does describe the problem, whereas "no ROM BASIC" does not, since the system in question would never call INT 18h if a bootable device were available (unless some insane programmer called it, and I seriously doubt that you can show me a commercially available program which does this). Glen 0/0

23 years, 7 months

6502 BASIC or Assembler and Intel 8271/WDC 1770 info req'd

by ajp166＠bellatlantic.net

From: Eric Dittman <dittman(a)dittman.net> >The third-party controllers were most popular on the Model 1, since the stock >FDC was SD. There were a few third-party controllers for the Model III and >the early Model 4, but they weren't as popular as the 1793 was more capable. >The stock Model 1 FDC also had reliability problems that lead to third-party >data separator plug-in circuits. Yep, the M1 data sep was the 1771 internal and that was at best terrible and WD would tell you that. That lead to the Piggyback card to at least add a decent data sep. The 1793 came later but was very desirable as the 35/40track Single sided FD100 or SA400 drives were tiny storage wise. Allison

23 years, 7 months

Grappler+ printer interface

by philip＠flatland.com

I realise this may not be the best forum to ask this question, but the emulator newsgroups seem to be pretty much dead. I'm updating an Apple ][+ emulator that I wrote back in 1994. I would very much like to emulate a printer interface card, such as the Grappler+, but I never owned a printer for the Apple ][+ I still have at home, so I don't have a printer interface card that I can study. So...I was wondering if anyone on this mailing list happens to own an Apple ][ with a printer interface card like the Grappler+, who would be willing to dump the ROM(s) and provide me with details of the I/O locations used. I realise some of you may be against distributing ROM code on the basis of copyright (I personally feel that discontinued products don't deserve copyright protection, though I realise the law says otherwise). If nobody is willing to provide me with ROM code for a printer interface card, I'll settle for a description of the I/O locations and any other information you can give me on the operation of the printer interface card, and I'll write my own "clean room" version of the ROM instead. Regards, Philip

23 years, 7 months

Hard Drives

by pete＠dunnington.u-net.com

On Oct 7, 16:50, ajp166 wrote: > Beats me what that drive is. This is a group for hardware over 10 years > old. > If it is that old you likely going to be fixing it yourself. > -----Original Message----- > From: CByrd87043(a)aol.com <CByrd87043(a)aol.com> > To: classiccmp(a)classiccmp.org <classiccmp(a)classiccmp.org> > Date: Sunday, October 07, 2001 3:48 PM > Subject: Hard Drives > > > >I have a Hard Drive model P1200-2af. I need to know where can I send it > to > >get it fix or replace. It just stop working. It's a nothing-special 1.2GB IDE drive with a bad reputation, made by JTS. JTS are no more, so the only likely option is to replace it with a Seagate, WD, or whatever. JTS were famous for, amongst other things, buying part of Atari from the Tramiel family, laying off a lot of staff, and then selling it to Hasbro shortly after being de-listed by the stock exchange and shortly before going bust in 1998. -- Pete Peter Turnbull Network Manager University of York

23 years, 7 months

Hard Drives

by ajp166＠bellatlantic.net

Beats me what that drive is. This is a group for hardware over 10 years old. If it is that old you likely going to be fixing it yourself. Allison -----Original Message----- From: CByrd87043(a)aol.com <CByrd87043(a)aol.com> To: classiccmp(a)classiccmp.org <classiccmp(a)classiccmp.org> Date: Sunday, October 07, 2001 3:48 PM Subject: Hard Drives >I have a Hard Drive model P1200-2af. I need to know where can I send it to >get it fix or replace. It just stop working. >

23 years, 7 months

DEC TK50-GA tape drive/ Windows 9x

by dittman＠dittman.net

> Now, it occurred to me that you may have thought "ohhh, DLT drive, 10 to 20 > GB per tape." and if that was the case I hate to disappoint you. You'd > would need to find a TZ89 rather than a TZ85. The 20GB uncompressed drive is the TZ88/DLT4000. -- Eric Dittman dittman(a)dittman.net Check out the DEC Enthusiasts Club at http://www.dittman.net/

23 years, 7 months

6502 BASIC or Assembler and Intel 8271/WDC 1770 info req'd

by dittman＠dittman.net

> > So now I'm left with two questions: > > 1) Has anyone got any source code for the WD1770? 6502 ASM, C, anything. > > The 1770 is pretty much compatible with the other Western Digital FDCs. > The TRS-80 model 4 uses the 1793 (very similar in software), and the > sources of LS-DOS 6.3.1 are on the web somewhere (Tim Mann's page?). > That's Z80 assembly language. The later (gate array) TRS-80 Model 4 systems used a 1773 FDC, which was compatible with the 1793. The 1770 and 1773 were compatible, differing only in the logic states of some of the lines, but it's been so long since I've used either I can't remember which pins were different. The 1770/1772/1773 had both the data separator and write precompensation built-in. They are 28 pin devices (the 1793 is a 40 pin device). -- Eric Dittman dittman(a)dittman.net Check out the DEC Enthusiasts Club at http://www.dittman.net/

23 years, 7 months

6502 BASIC or Assembler and Intel 8271/WDC 1770 info req'd

by dittman＠dittman.net

> > The later (gate array) TRS-80 Model 4 systems used a 1773 FDC, which was > > Interesting. The older model 4s (like mine) have a 1793 -- the floppy > controller board is indentical to that in a model 3. I'd assumed they > used that board in the gate array versions as well. > > Maybe they did (in the early gate array machines), and then changed to > the 1773 for the last ones. I don't see any reason why that couldn't have > been done -- as you said the 1773 and 1793 are pretty much compatible. The early systems weren't gate array systems. The gate array Model 4 and 4P systems had the FDC and RS232 integrated on the mainboard. If you have a separate FDC and/or RS232 board then your mainboard is not a gate array model. -- Eric Dittman dittman(a)dittman.net Check out the DEC Enthusiasts Club at http://www.dittman.net/

23 years, 7 months

ZX81 kits (was Re: Keep or assemble???)

by acme_ent＠bellsouth.net

> > The ULA does a lot more than handle the display ;>) > > CPU clock generation (which would be useful). Address decoding (which I'd > want to modify if I was changing the amount of RAM). Very interesting -- how much RAM are you talking about adding that you have to modify the address decoding? > > Of course not ;>) But a ZX81 kit is still faster than starting from > > scratch. > > Is it? It's not going to take long to wire-wrap a clock circuit and > address decoder, and stick in the Z80. It depends _very much_ on how much > of the ZX81 you want to use... Which in turn depends on what the intended use of the finished device is. Since I want a "general purpose" computer the ROM BASIC functions are very convenient, and fast if called directly. Other applications of the Z80 would not need this code so a quickie Z80 board would be fine. > > Try desoldering the RF modulator from a ZX81 board ;>) > > Well, I had never tried to do it before, so I grabbed a ZX81, What, do you have a pile of these? > unscrewed > the case and attacked it with soldering iron and sucker. > > What's the catch? In the US versions which have 3 thin wires, they sometimes become brittle and break. Tony (and others), a question: in your opinion, which microprocessor was the most well-designed (even if not implemented)? Glen 0/0

23 years, 7 months

Hard Drives

by CByrd87043＠aol.com

I have a Hard Drive model P1200-2af. I need to know where can I send it to get it fix or replace. It just stop working.

23 years, 7 months

6502 Source....

by pete＠dunnington.u-net.com

On Oct 7, 17:14, Alex White wrote: > Hey all UK people - do you know of a source for 6502s (and related support > chips, such as the 6522) within the UK? Farnell still list the CMD version, G65SC02, catalogue number 562-750, and the Rockwell R65C102, cat.no. 388-488, though the Rockwell parts is listed as "available until stocks are exhausted". They also list several varieties of 6520, 6521, and a 6545 (Rockwell version of 6845 CRT controller), but I know of no suppliers for new 6522s. -- Pete Peter Turnbull Network Manager University of York

23 years, 7 months

Is there a source for veroboard in the U.S.?

by erd_6502＠yahoo.com

I wanted to bang out a quick thing involving bussed lines (an LED display for a Dragon's Lair game, if you're curious). I thought it might be quick to do with veroboard as opposed to point-to-point wiring. I want to make a prototype before considering burning a board (since that's a weakness I have at the moment anyway - lack of knowledge about layout tools). The problem is that I haven't seen veroboard for sale in the States, only the U.K. and perhaps Western Europe. Here, we have lots of modular prototyping board, but it's not easy to use when you have a lot of parallel connections (like a data bus). Are there any sources on this side of the pond? If not, how much does a sheet of about 6"x9" cost? If it's too expensive to buy and ship, I have several square feet of plain blue perfboard I got from the Micro Center when they put all their hobbyist stuff on remainder, and I'll build it from scratch. I went to school in England in 1985 - New College, specifically, down the street from Blackwell's Books. I spent many hours there absorbing everything I could about hardware hacking (not having the budget to _buy_ the books - the Turf Tavern was closer to the gate ;-) I remember a couple books with do-it-yourself projects using veroboard. Now I wish I'd gotten more books and less beer (but it was _great_ beer) :-) Any veroboard pointers? Thanks, -ethan __________________________________________________ Do You Yahoo!? NEW from Yahoo! GeoCities - quick and easy web site hosting, just $8.95/month. http://geocities.yahoo.com/ps/info1

23 years, 7 months

IBM ROM BASIC or lack thereof

by acme_ent＠bellsouth.net

Tony Duell wrote: > Since they never did provide BASIC they had to make INT 18 do something > (remember an application program could, in theory, call that interrupt). > Since that interrupt should have entered ROM BASIC, the most sensible > thing to do was to print that there was no ROM BASIC and then halt the > CPU. Since "they never did provide BASIC" then there was *always* "no ROM BASIC." That's like stopping the machine with a message stating "no printer." Why not display something understandable to a common user, such as "no bootable device?" Glen 0/0

23 years, 7 months

6502 BASIC or Assembler and Intel 8271/WDC 1770 info req'd

by philpem＠bigfoot.com

On Sat, 6 Oct 2001 at 01:25:28 +0100 (BST), ard(a)p850ug1.demon.co.uk (Tony Duell) said: > > BTW, I also need some info on the Intel 8271 disk controller - I've got two > > I would not do a new design using the 8271. The chip is fairly hard to > find now, and there are machines that _need_ them (like the old Acorn > Systems). OK, then. One 8271, starting bid $100 - just kidding :-) > In fact, I'd probably use one of the all-in-one PC floppy controller > chips unless there was a very good reason not to. Add a crystal and > perhaps some cable driver chips. That's all... Is "I don't know any suppliers for PC FDCs" a good reason? Farnell Electronics don't seem to sell them, nor do Maplins, Electrovalue, ESR Electronics or any other supplier I know. Care to tell me where I can get them? > > of these little devils and Intel's datasheet makes absolutely no sense at > > all. I've also got a Western Digital WD1770-PH 00-02 that I might be able to > > use instead. First of all, which is the better controller? The 8271 or the > > 1770? Also, is it possible to overclock a 1770 or an 8271 like you can a > > 1772? > > Oh, use the 1770. It does double density (MFM) for one thing (the 8271 is > single-density only). It also require many fewer support circuits I > think. OK, then. The 1770 it is. > The 1770 and 1772 are closely related (the difference being the step > rates the chips can produce). I would guess that the 1770 can be > overclocked, but I've never tried it. I think I'll keep it running at the normal speed (8MHz). But the machine will have a 16MHz oscillator and a divider, with a few jumper blocks for clock speed selection (8 and 16MHz for the FDC, 1, 2 or 4MHz for the 6502 and support circuitry). I've got two Western Design Center W65SC02s (14MHz 6502s! Woohoo!) to play with, plus a Synertek SY6502A (the 2MHz one), two W65SC22s (10MHz WDC 6502s) and two Synertek 6522s (1MHz). So now I'm left with two questions: 1) Has anyone got any source code for the WD1770? 6502 ASM, C, anything. 2) Has anyone got a schematic for a fairly half-decent 16-colour (or better) video card that can be modified to work on a 6502? I've had a look at the NASCOM schematics but I've heard Bad Things(tm) about the NASCOM video system. Aparrently Gemini and a few others produced colour video cards for the NASCOM. Anyone got schematics for these? Graphics would also be nice (the NASCOM video system is text only). BTW, I'd like to avoid obsolete components if that's at all possible. I've got a Hitachi HD6845 but if the 40-odd page datasheet is anything to go by, it's a real dog to use... And it only works in monochrome. I have got a MOS Tech 6568(?) VIC-II, the same one used in the UK Commodore 64. The PSU for this C64 is fried, took out some of the support components with it. TIA. -- Phil. philpem(a)bigfoot.com http://www.philpem.f9.co.uk/

23 years, 7 months

6502 BASIC or Assembler and Intel 8271/WDC 1770 info req'd

by dittman＠dittman.net

> The 1772 and 1770 were designed specifically for use with the 5-1/4" units, > though that's not necessarily what their use today may be. > > I've never seen the 1773 in the flesh, though I've got a data sheet somewhere > (though I've managed to hide it somewhere). The three chips are all similar, > though not identical, in that they have the same data/clock separator circuitr > and write precomp circuit. However, the 1773 lacks some signals that are on the > 1770/72, thereby rendering it less "dedicated" to 5-1/4" drives. The datasheet > did, IIRC, specifically indicate that they're all similar in commands, etc, > though the timing parameters differ somewhat in that the 1770 is slower than the > otherwise identical 1772 in terms of its step rate settings. If I could lay > hands on the 1770/2/3 datasheet, I could tell you which pins differ and in what > sense, but ... The 1773 is also dedicated to 5.25" drives. Your email jogged my memory, and indeed the difference between the 1770 and 1773 was a couple of different signals. I've used the exact same code on both of them. From a programming point of view they are the same. I don't think there was a version of the 1773 with the faster step rates like in the 1772. > If somebody's got a 1773 and wants a 1770, I'll happily swap 'em, just so I have > one in house. If you find a gate array TRS-80 Model 4 then you'd have your 1773. -- Eric Dittman dittman(a)dittman.net Check out the DEC Enthusiasts Club at http://www.dittman.net/

23 years, 7 months

ZX Spectrum internals (Was: ZX81 kits)

by pete＠dunnington.u-net.com

On Oct 7, 2:17, Iggy Drougge wrote: > >> >If it's another 40 pin chip, then that's the custom ULA chip that > >> >includes most of the glue logic. > >> > >> Is that like a lot of 74138s or something? > > >It's rather more than that (I assume that's the address decoder part, > >which is in the ULA). It also handles the DRAM timing, most of the video > >display, and so on. > > I thought one of the selling points of the Z80 was its built-in ability to > handle DRAM. But perhaps it's lacking the 6502's ability to easily share > memory with other devices by only doing memory accessing every second or > fourth cycle. The Z80's special ability in handling DRAM is merely the presence of an on-board counter which increments once in every instruction cycle, and which is output onto the address bus once per instruction. This is only part of the requirement, however (see below). The refresh counter means the chip is guaranteed to cycle through the addresses (with no omissions) in a given period. This is exactly what you need for DRAM refresh. Of course, if you have a video circuit accessing the same DRAM, it too will cycle through the address range (or part of it) and achieve the same end, so the Z80 refresh is only a useful bonus if you don't have video accessing your DRAM. Anyway, it's only a 7-bit counter, which is fine for 16Kbit DRAM but not for most 64Kb devices. The downside is that a Z80 uses the clock in a different way from a 6502. A 6502 does some things on one half of the clock cycle (like accessing memory to read instructions or read/write data) and other things (internal operations) on the other half cycle. During the half-cycle when it doesn't need memory access, it releases the bus, leaving it free for use by other devices (eg video). A Z80 uses successive cycles (of a faster clock) instead of alternate half-cycles for different purposes and there is no clock state when it's guaranteed not to be using the bus. However, there is one (whole) clock cycle when it doesn't need the bus, and that's the refresh period; it's just more complicated to decode that than to just use the phase of the clock (high or low) to enable your video access (or whatever). It's also less suitable than the 6502 since Z80 instruction cycles vary in length and therefore the interval between refresh cycles is not constant. The interval between successive half cycles of a 6502 clock is (usually!) constant. I said the refresh was only part of the requirement. That's because DRAM normally splits the address into two parts, row addresses and column addresses, to address a given cell in the memory matrix. Usually these two parts of the address are multiplexed onto the same pins of the IC. Therefore, on the first part of the memory access cycle, you put the row addresses on the pins and signal this to the DRAM with the /RAS (row address select) signal. The IC latches these address bits internally, and after some time period, you turn off /RAS, replace the row address bits with the column address, and apply the /CAS signal. Neither the Z80 nor the 6502 have any special feature to simplify this (unless you count the fact that you have two clock phases per memory address on a Z80). So in a Spectrum, ZX81, etc, the ULA takes care of the address multiplexing and RAS/CAS timing. > But what does glue logic really mean? Just slang for the assorted logic that does address decoding, signal buffering, RAS/CAS generation, etc. In a typical system with, let's say, ROM, RAM, processor, some I/O ports, perhaps a DMA device, each section that connects to the address/data bus (and perhaps the control bus too, if DMA is involved) would have its own set of buffer ICs, each being enabled only when the relevant section is accessing the bus. The glue logic includes all the decoding/multiplexing of the address and control signals. If you think of a system as CPU, RAM, ROM, I/O ports, then the glue logic is all the extra circuitry you need to "glue" them together into a working system. > Couldn't Sinclair have socketed the BASIC? It must have been a lot of work to > piggy-back it onto each imported Spectrum, unless the customers had to do it > by themselves. Sinclair never used sockets if they didn't have to, for reasons of both cost and reliability. If there was a special Sinclair-original ROM for Scandinavian countries, I would have expected that to be factory-fitted instead of the standard ROM. It's possible they retrofitted something like that -- it might be cheaper to piggyback a new ROM instead of removing the old one -- but I would guess that what you have is something done by the original owner, in order to have both systems. Sinclair would be most unlikely to fit something as extravegant as a switch. -- Pete Peter Turnbull Network Manager University of York

23 years, 7 months

older SGI and Mac equipment available for free

by mcguire＠neurotica.com

Hey folks. I've got four or five SGI Personal Iris machines here...4D20, 4D25, and 4D35, in various configurations and in various states of operability. I also have three Macintosh Quadra 950s. I offer them for free to any interested party for pickup in Laurel, MD within the next two weeks or so. I am moving, and they need to go. In addition, there's a list of [non-free] stuff that I have available at http://www.neurotica.com/available.html. -Dave -- Dave McGuire Laurel, MD

23 years, 7 months

Found WANG boards

by optimus＠canit.se

While visiting my electronics shop, I found a collection of largish cards (circa 15?25 cm?) made by WANG. There were at least two video cards - one IBM mono emulator card and one low-res cards. There was another card with two BNCs and a switch, could be a grpaihcs card, too. There was a winchester controller as well, and some card which I couldn't identify. If anyone's really interested, I'll see how much he wants (probably very little, they're sold as scrap). -- En ligne avec Thor 2.6a. G? med i SUGA, Swedish Usergroup of Amiga! WWW: http://swedish.usergroup.amiga.tm/ BBS: 08-6582572, telnet sua.ath.cx, port 42512.

23 years, 7 months

CBM8032 - wobbly screen (The saga continues)

by Innfogra＠aol.com

In a message dated 10/6/01 3:35:56 PM Pacific Daylight Time, ms(a)silke.rt.schwaben.de writes: > call "mu-Metal", which is a special alloy of steel and other things i > have long > forgotten but that make it EXPENSIVE. > It is magnetic, but not a good conductor, which make it ideal for > shielding magnetic > fields Mu metal should be easily scroungable. It is the shielding on old large graphic monitors, Convergent "N"gens and many other pieces of electronic gear. Often found around CRTs and CPUs. Tektronix used a lot of it. It is soft and usually a dull gray although sometimes silvery. Occasionally it shows a crystal type surface. It is magnetic and not a good conductor. It is expensive new. We got up to $5 per pound for it, scrap, at one time. Paxton Astoria, OR

23 years, 7 months

Hardware races

by KenzieM＠sympatico.ca

On another list someone mentioned that a PDP11 ran at about the same speed as a 486-66. I don't have a 486-66 but do have a PDP11/34 in the garage so I suggested that if a 486-66 could be found we could have a race. I tested the capacitors on the weekend and they were OK, still need to test the RL01 drives and get them hooked up. >From the cables in the cabinet and the terminator on one of the drives I'm guessing that they are daisy chained. A few questions remain. What would be the best way to test the Power supply it is currently off the chassis, does it need to be connected for testing? Any suggestions for a fair race? Recent additions: Unisys PW2 (Unisys ICON NETWORK), Microcom (apple clone), SHARP PC4500 Collector of Vintage Computers (www.ncf.ca/~ba600)

23 years, 7 months

6502 BASIC or Assembler and Intel 8271/WDC 1770 info req'd

by philpem＠bigfoot.com

Hi, I'm building myself a 6502-based single-board computer, with the aim of running it off a 4.8V NiMH or NiCad battery pack. But I've got a problem. I need a programming language for it. Aparrently there were many BASIC interpreters sold for the Synertek SYM-1 (aka SY-VIM-1), MOS KIM-1 and Rockwell AIM-65. Anyone know what happened to the companies that produced these? Ideally I'd like the source code for a 6502 BASIC interpreter, but binary code would be OK too. The SBC will communicate via a small LCD panel, RS232 (so I can hook it up to a "dumb terminal") and will have a hexadecimal keypad and an optional hard drive, too. Anyone care to make any suggestions (or submit some code)? BTW, I also need some info on the Intel 8271 disk controller - I've got two of these little devils and Intel's datasheet makes absolutely no sense at all. I've also got a Western Digital WD1770-PH 00-02 that I might be able to use instead. First of all, which is the better controller? The 8271 or the 1770? Also, is it possible to overclock a 1770 or an 8271 like you can a 1772? I'd love some schematics and/or some source code. I really don't fancy disassembling Acorn's 8271 DFS and Watford Electronics' 1770 DFS... Thanks. -- Phil. philpem(a)bigfoot.com http://www.philpem.f9.co.uk/

23 years, 7 months

Restoring classic kits we built way-back-when

by erd_6502＠yahoo.com

We've had the ongoing debate of "build a ZX-81 kit or leave it in the box", but one aspect of classic kit building I have a question for the group about is, what about stuff that we built ourselves 10+ years ago that still works, but might need some touch-up. Specifically, I have several things (a TVT-6, a Cosmac Elf, a homemade arcade button panel for playing Space Invaders on a PET, a 2-char LED display for the PET, etc.) that I made when I was a teenager. They still work, so it's not a question of repair. It's an aesthetic thing - my soldering skills were much poorer when I was 13. I'm debating re-soldering these items (and risking breaking them) or leaving them the way they are a) because if it works, don't screw with it, and b) it's a snapshot of my own context in the greater historical framework. I took history and archaeology in school; I have a strong aversion to modernizing artifacts. When restoring pots, statues, mosaics, etc., an archaeologist tries to never restore an antiquity in a way that can't be reversed (they use water-soluable glue made from fish scales to move mosaic fragments, for example). Also, when modern materials are used, no attempt to make it resemble the ancient material is made - quite the opposite - it's plainly and intentionally modern looking so ever a casual observer can't mistake it for the missing original. When my advisor restored the bed of a large monochrome mosaic near Isthmia, he threw several modern coins into the concrete bed so that future excavators would know that it wasn't ancient concrete. So re-soldering my TVT-6 makes it look nice, but dilutes the fact that it was originally built in the 1970s, just as much as using modern ICs does. Do people have an opinion about this? Am I just stuck on the horns of a false dilemma? -ethan __________________________________________________ Do You Yahoo!? NEW from Yahoo! GeoCities - quick and easy web site hosting, just $8.95/month. http://geocities.yahoo.com/ps/info1

23 years, 7 months

CBM8032 - wobbly screen (The saga continues)

by mythtech＠Mac.com

>4th attempt: Removed all tinfoil, started up with the lid open, no wobble. >The wobble appears progressively as the monitor approaches the transformer >(the lid down position). Knowing NOTHING about the unit you are working on... two things pop in my mind from my TV/VCR repair days. 1: Is it possible the controller on the back of the tube is loose? When you tilt the lid (and from what I gather, the tube with it) back into place, maybe the board is shifting from the change in weight position. 2: Is there a cable or wire that is getting pulled on when you close the lid? Maybe one of them has a bad solder joint, and the joint stays properly closed when the lid is open, but when closed, gets pulled (or pushed), and breaks the connection. Have you tried, while the unit is open, to jiggle any wires that might be effected (obviously, don't do them with your hands, use a non conductive spudger or similar tool... wouldn't want you to kill yourself by grabbing the wrong wire) Again, I know NOTHING about the unit you are working on, so these were just shots in the dark thinking maybe something will help. -chris <http://www.mythtech.net>

23 years, 7 months

older SGI and Mac equipment available for free

by mcguire＠neurotica.com

On October 6, LFessen106(a)aol.com wrote: > Hey Dave, can you hold onto a Quadra for me? Sure, if you can grab it before I move...end of October... -Dave -- Dave McGuire Laurel, MD

23 years, 7 months

CBM8032 - wobbly screen (The saga continues)

by ajp166＠bellatlantic.net

What you need is Mumetal which is a MAGNETIC alloy. Lacking that distance helps. Having built numrous O'scopes over the years the problem of transformers radiating magnetic fields are well known to me. Allison -----Original Message----- From: Adrian Vickers <avickers(a)solutionengineers.com> To: classiccmp(a)classiccmp.org <classiccmp(a)classiccmp.org> Date: Saturday, October 06, 2001 3:39 PM Subject: Re: CBM8032 - wobbly screen (The saga continues) >Curiouser and curiouser... > >Today, I happened to have the machine opened up to effect some keyboard >repairs (i.e. a jolly good clean up). Having successfuly removed all traces >of key bounce, non-working keys, etc., and feeling justifiably please with >myself, it occurred to me to try a couple of things WRT the wobbly screen. > >1st attempt: "build" some shielding out of aluminium foil to go around the >transformer. Which I did - all rough & ready stuff, with just a bit of >insulating tape over the transformer connections to make sure they didn't >short out. No effect - the screen wobbled its way along as ususal. > >2nd attempt: Same as above, but this time I made absolutely sure the tin >foil was earthed, by screwing it onto the chassis via one of the >transformer screws. Same effect as 1st attempt: FA. > >3rd attempt: Getting desparate now, I wrapped a load of tin foil around the >signal cables (having removed it from the transformer). Decided to leave >the lid up when I switched on and bingo! Steady as a rock (literally no >movement whatsoever. Refusing to get too excited, I carefully brought the >lid down (holding the signal cables so as not to let the tin foil touch the >circuit board - bah! The wobble returned. > >4th attempt: Removed all tinfoil, started up with the lid open, no wobble. >The wobble appears progressively as the monitor approaches the transformer >(the lid down position). > >5th attempt: Put a sheet of tinfoil over the whole of the bottom of the >monitor section. No effect - wobble remained. > >Clearly, therefore, the wobble is induced by the monitor. There must be a >fairly monster field coming off the transformer interfering with the >electron gun aiming circuit(s), or something like that. > >The question is: What *would* shield it? Do I need some thin steel or >copper, for example? Presumably, the shielding needs to be earthed (not >difficult, there's plenty of earth points around there. Or, would it be >easier to simply replace the big transformer with a smaller modern one? > >TIA! >-- >Cheers, Ade. >Be where it's at, B-Racing! >http://b-racing.co.uk >

23 years, 7 months

← Newer
1
...
23
24
25
26
27
28
29
30
31
Older →

Jump to page:

2025

2024

2023

2022

2021

2020

2019

2018

2017

2016

2015

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

test-drb October 2001