Re: Resending: Repairing a SFD-1001 (8250/LP, 8050, 4040, 3040, 2040)

From: Steve Gray <sjgray_at_rogers.com>
Date: Tue, 9 Aug 2011 09:16:44 -0700 (PDT)
Message-ID: <1312906604.22808.YahooMailRC@web88606.mail.bf1.yahoo.com>
Hi,

On a related note, I have successfully replaced the power supply of an 8250LP 
drive with a very small switching supply bought from ebay for a few dollars. You 
wouldn't believe how heavy those 8250LP supplies are. Anyway, the replacement 
supply ouputs 5V @ 2A and 12V @ 2A using the same connector as used on PC floppy 
and IDE hard drives. If anyone needs info or pictures please let me know.

Steve



----- Original Message ----
> From: Wolfgang Moser <womo@news.trikaliotis.net>
> To: cbm-hackers@musoftware.de
> Sent: Tue, August 9, 2011 2:36:17 AM
> Subject: Resending: Repairing a SFD-1001 (8250/LP, 8050, 4040, 3040, 2040)
> 
> Hello hackers,
> 
> unfortunately the first version of this mail article didn't made its way
> onto the list, either because of crude formatting or because of using a
> news2mail-gateway or both. Now I removed the attachement, please get it
> from:
> 
>     http://xw15.de/cbmstuff/Universal-Floppy-Dumper-20110807.zip
> 
> 
> Read on for my first mail, Womo
> 
> -=-=-=-=-=-=-=-=-=--=-=-=-=-
> 
> Hello hackers,
> 
> this article is about my successful repair attempts to resurrect at
> least the electronic parts of a batch of SFD-1001 floppies, a 8250LP and
> a 8296D. It will be followed by two other articles where I will call for
> your help regarding the mechanisms and specific ROM contents.
> 
> In April this year Tommy Winkler released a first version of a firmware
> for Nate Lawson's ZoomFloppy (USB connected backend for OpenCBM) with
> support for Commodore IEEE disk drives. Because we always planned to
> have support for IEEE drives within the ZoomFloppy and already designed
> the hardware to support these, I collected some SFD-1001 drives and such
> alikes from eBay for two years or so. Most of them were not working or
> in bad condition otherwise. For example the 8250LP is missing its top
> cover. From a series of auctions where a german sold the bequest of his
> father I got some five or so additional SFD-1001 mainboards and an empty
> case in mint condition with power supply and metal cage.
> 
> With this I started my repair attempts. Two drives very relatively easy
> repaired by only checking the blink codes and swapping some chips more
> or less systematically. Since one of these didn't produce sane results,
> when tested with the ZoomFloppy I changed the mainboard with one of the
> spares and voila, I had two working drives.
> I then started with checking all the socketed chips from all SFDs and
> the 8250LP and found one defective 6532 RIOT and two defective 6530
> RRIOTs aka 901885-04. A 6530 from one of the drives was missing, missing
> 6532 chips could be replaced with chip that I pulled from the spare
> mainboards.
> 
> A third drive could be assembled from the spare case with the known good
> power supply. One mechanism needed a thorough head cleaning procedure:
> 1) getting a tissue, folding it and then placing it between two R/W
> heads with the door closed, 2) saturating the tissue with isopropyl
> alcohol, repeating the saturation every five minutes and letting it
> solve all the dirt at the heads for 30 minutes or so, 3) mechanically
> cleaning and polishing the heads with a standard head cleaning diskette
> and the recommended procedure.
> 
> For a fourth SFD-1001 drive one of the remaining power supplies could be
> repaired as well as the mainboard by getting a last working 6530 out of
> the 8296D. Unfortunately I ran out of working mechanisms. I did not make
> systemtic checks of all the remaining mechanisms from the SFD, 8250LP
> and 8296D since I decided to first work for a solution on another problem...
> 
> 
> Where to get new 6530 chips?
> ============================
> 
> Answer: Nearly nowhere. As I found out from different discussions it
> seems to be a problem for nearly a decade or so to get any replacement
> parts for the 6530, especially the mask programmed version for the SFD
> and similar drives. As Nicolas Welte pointed out in several such
> discussions, the 6530 not only has a mask programmed ROM, but also a
> mask programmed logic. This is something that could be compared with
> ASICs from manufacturing principles as of today.
> 
> In the SFDs and 8250LPs Commodore did not make use of an own customised
> 6530 with a dedicated logic and ROM mask, but reused chip from the older
> drives like the 8050. They simply ignored the 6530 internal masked ROM
> and replaced it with an EPROM with new contents with the help of a
> little adapter board. So this means that the programmed logic gate masks
> for the 6530 were all the same or at least nearly identical to be reused
> in other floppy types with small external adaptions.
> 
> In all the discussions from above Nicolas and perhaps some other people
> also often mentioned that it should be possible to replace a 6530 with a
> 6532, an additional ROM chip and some logic to recreate the internal
> programmed logic gate mask. One needs "only" to find out about the
> concrete implementation of that programmed logic.
> 
> So the way to go for getting 6530 replacements was defined.
> 
> 
> How to create a 6530 replacement from a 6532?
> =============================================
> 
> Meanwhile, perhaps initiated by these discussions form the past some
> others already showed that such an adapter is infact possible to create.
> French pinball enthusiasts created an "adapteur" to replace defective
> 6530 chips in some Gottlieb Sys1 and Sys80 soundboards for pinball
> machines. A german company sounds a very similar board named
> "MIOT-Adapter". And finally the Micro-KIM replica of the MOS
> Technologies KIM-1 single board computer was created by Briel Computers
> and it came with an integrated replacement circuitry for the two 6530s
> of the KIM-1.
> 
> Last but not least there is probably the mother of all these existing
> 6530 replacement circuits. Ruud Baltissen's "Build your own KIM-1" page
> where he described all the oddities about how the create a replacement
> for the 6530 by using a 6532, a ROM and some "glue" logic.
> 
> This showed to me that such a replacement must be doable also for the
> Commodore floppies. I also was willing to find a way to get a 100%
> compatible solution for the "fourth" problem described by Ruud. I looked
> out for a way so that the additional 6532 IRQ generation method which
> depends on the behavior of PA7 cannot be enabled anymore.
> 
> 
> But at first the "fifth" difference, "the last and major one" needed to
> be solved, "the way the registers ..." of the 6530 "... are selected" in
> the Commodore floppy disk drives, namely the SFD-1001, 8250LP, 8296D,
> 8250, 8050, 4040, 3040, 2040.
> 
> 
> Analysing the CBM floppies' memory maps
> =======================================
> 
> From old Funet.FI files (now on zimmers.net) I saw that at least three
> people already did investigate the memory map of the floppy disk
> controller of different CBM floppies. And they wrote some programs for
> this purpose. Olaf 'Rhialto' Seibert described the memory maps both for
> the bus controller (BC) and the disk controller (DC) as well of a 8250
> floppy disk drive. He also described a little routine executed as job
> code to copy one memory page from the DC onto the shared memory between
> the DC and BC. Afterwards standard M-R commands could be used to read
> out the contents from this buffer.
> 
> William Levak used a similar routine and composed a memory map for the
> 4040 disk drive based on readout results. And then there is Andre Fachat
> whose program is not much different to the one from William, but also
> provides one which can be used to download the BC's ROM.
> 
> 
> Except for Williams memory map analysis for the 4040 drive, no
> information could be found in the net for all the other drives.
> Therefore I investigated memory maps on my own for the SFD-1001 and
> 8250LP. I also wrote my own tool which is able to a) read out the whole
> adressable 64KiB map of the DC (although actually only unmirrored 16KiB
> adress space are adressable by the CPU), b) read out the whole address
> 64KiB map of the BC and c) it does /not/ leave the floppy in stuck
> condition so that it needs to be reset afterwards. Please find a listing
> of the floppy side code as well as a little bash shell script which uses
> OpenCBM cbmctrl calls to control the uploaded floppy routine attached to
> this article. The shell script should be easily convertable to standard
> Basic commands since OpenCBM cbmctrl is nothing else than a simulation
> of standard IEC/IEEE commands.
> 
> 
> Creating a 6530 replacement circuit
> ===================================
> 
> With additional read out address maps from all my working SFD drives and
> the 8250LP (only the electronics part is working yet) I recognised that
> the 6530 internal decoding depends on /CS2, RS0, A6 and A7 only. With
> the two existing Chip Select inputs from a 6532, the required glue logic
> could be reduced to two NOT gates. One is needed to enable the extra ROM
> chip whenever PHI2 is high (same as on the Commodore adapter boards),
> the other is needed to invert A6 is 6532-CS1 input while CS2 is
> connected with 6532-CS2. To have a more clean design PHI2 should be
> NANDed with R/W which is then used as ROM enable. RS0 is used as ROM
> output enable while A7 is connected to 6532-RS.
> 
> Above I wrote that I wanted to have Ruud's "fourth" difference between
> the 6530 and 6532 be solved. This objective was reached by connecting
> 6532-A4 to a fixed high level. That way the described IRQ method cannot
> be enabled anymore (check the datasheets). A4 from the 6530 chip socket
> was connected with 6532-A6 instead. The latter effectively halved the
> 6532's RAM size from 128 Bytes to 64 Bytes. In the end this measure
> improved overall compatibility of the 6530 replacement in two points:
> supported IRQ methods and RAM size.
> 
> Currently the chosen Flash ROM is 32KiB in size. Smaller ROMs are not
> available for reasonable prices. Therefore I decided to pack as much as
> possible different FDC drive ROMs into it and make all the banks
> selectable by DIP switches. With this it should be possible to support
> all drive DOS ROM versions of all Commodore dual CPU drives with only
> one final circuit and firmware. Currently I don't know how many such
> ROMs do exist, therefore one of the follow-up articles will follow.
> 
> 
> Supporting SpeeDOS 2K FDC ROMs
> ==============================
> 
> Since nearly all TTL chips contain more gates than I needed for the
> circuit I tried out, if the 8250/8250LP EDOTRONIK SpeeDOS system could
> be supported by an alternative configuration option. And it was possible
> by using a 4-NAND gates chip. Switching from 1KiB FDC-ROM support to
> 2KiB support means that A10 DIP switch configuration option is lost and
> only 16 different ROM images can be supported with a 29C256 chip (or
> 28C256, 27C256, ...). When a 27C512 EPROM is used, maybe 32 different
> 2KiB ROM images could be used (untested).
> 
> Since the 1KiB/2KiB option could be selected with a pair of jumpers even
> mixed 1KiB and 2KiB ROM images could be stored within the same ROM chip,
> so I hope that a '256 ROm chip is enough for all existing ROM image files.
> 
> 
> Current state of the development
> ================================
> 
> In the last months a hand wired prototype was developed, debugged --
> Commodore mixed up PHI2 and R/W in the schematic of the 6530 adapter
> board which costed me at least eight weekends of debugging with a mixed
> signal o'scope and logic analyser -- then successively extended by the
> SpeeDOS option and tested again. Several other circuitry alternatives
> were constructed, optimised and tested until the current design was
> chose which only needs one TTL chip for the glue logic. No GAL, no
> difficult to find exotic components, just standard and easy to get parts.
> 
> Currently only a SFD-1001 drive was tested thoroughly by the replacement
> adapter and only from an electronics point of view. I don't know of any
> good testing programs that could check, if there remain any
> compatibility problems from the replacement.
> 
> I have plans for creating a profesionally manufactured PCB and already
> created a layout that fits into a 8250LP and a SFD-1001 as well. I don't
> know, if the same design would also fit into the 8250, 8050, 2040, 3040,
> 4040 and perhaps some other suitable drives.
> 
> 
> What else?
> ==========
> 
> Before declaring that little project as being finished I would like to
> discuss some remain topics with you. The first one is about available
> ROM image files about all the different FDC-ROM versions that are
> documented by Commodore, but not available up to date (e.g. the FDC-ROM
> from the 2040's DOS-1). Please see my follow-up article on this topic
> which I will write up the next weekend or so. Next I would like to
> discuss options about repairing the mechanisms in the 8250LP and
> SFD-1001 disk drives or perhaps options about replacing the mechanism
> with a drive from a different manufacturer. To me it would not make any
> sense to have a 6530 replacement, when I'm still not able to repair the
> mechnisms.
> 
> Maybe, if there is some interest in it and if we find solutions for all
> the other top-10 defects for all the old CBM disk drives, then a final
> 6530 replacement adapter could by available by the end of the years. But
> this would require also that someone else finds a source for 6532 chips.
> If the 6530 chips are impossible to source nowadys, the 6532 ones are at
> least very hard to find in new and factory packaged condition.
> 
> 
> 
> Womo
> 
> PS: If someone else also collected defective CBM drives and was
> successful in repairing some of them, maybe there is an option to
> exchange some parts. Currently I'm searching for at least five 100 TPI
> mechanisms used in the SFD-1001 and 8250LP drives. I would be willing to
> give away my original and working 6530 chips and perhaps some other
> electronic parts since now I know how to replace them and I already got
> some spare 6532 chips years ago.
> 
> -- 
>   ------ to obtain more infos about me, look up the page ------
>     ------ http://www.wmsr.de | wm (at) wmsr (dot) de  ------
> 
> 
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> 

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Received on 2011-08-09 17:00:12

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